results for au:He_H in:hep-ex

- Jan 12 2018 physics.ins-det hep-ex arXiv:1801.03620v2A measurement is reported for the response to charged particles of a liquid scintillator named EJ-335 doped with 0.5% gadolinium by weight. This liquid scintillator was used as the detection medium in a neutron detector. The measurement is based on the in-situ $\alpha$-particles from the intrinsic Uranium and Thorium contamination in the scintillator. The $\beta$-$\alpha$ and the $\alpha$-$\alpha$ cascade decays from the U/Th decay chains were used to select $\alpha$-particles. The contamination levels of U/Th were consequently measured to be $(5.54\pm0.15)\times 10^{-11}$ g/g, $(1.45\pm0.01)\times 10^{-10}$ g/g and $(1.07\pm0.01)\times 10^{-11}$ g/g for $^{232}$Th, $^{238}$U and $^{235}$U, respectively, assuming secular equilibrium. The stopping power of $\alpha$-particles in the liquid scintillator was simulated by the TRIM software. Then the Birks constant, $kB$, of the scintillator for $\alpha$-particles was determined to be $(7.28\pm0.23)$ mg/(cm$^{2}\cdot$MeV) by Birks' formulation. The response for protons is also presented assuming the $kB$ constant is the same as for $\alpha$-particles.
- The Dark Matter Particle Explorer (DAMPE) satellite detector announced its first result for measuring the cosmic-ray electron/positron (CRE) energy spectrum up to 4.6TeV, including a tentative peak-like event excess at (1.3-1.5)TeV. In this work, we uncover a significant hidden excess in the DAMPE CRE spectrum over the energy range (0.6-1.1)TeV, which has a non-peak-like structure. We propose a new mechanism to explain this excess by a set of 1.5TeV $\mu^\pm$ events with subsequent decays into $e^\pm$ plus neutrinos. For explaining this new excess together with the peak excess around 1.4TeV, we demonstrate that the \it flavor structure of the original lepton final-state produced by dark matter (DM) annihilations (or other mechanism) should have a composition ratio $N_e : (N_\mu +\frac{1}{6}N_\tau) = 1 : y$, with $y \simeq 2.6-10.8$. For lepton portal DM models, this puts important constraint on the lepton-DM-mediator couplings $\lambda_e : (\lambda_\mu^4 + \frac{1}{6}\lambda_\tau^4)^{\frac{1}{4}} = 1 : y^{\frac{1}{4}}$ with a narrow range $y^{\frac{1}{4}} \simeq 1.3-1.8$.
- The ARGO-YBJ experiment, a full coverage extensive air shower (EAS) detector located at high altitude (4300 m a.s.l.) in Tibet, China, has smoothly taken data, with very high stability, since November 2007 to the beginning of 2013. The array consisted of a carpet of about 7000 m$^2$ Resistive Plate Chambers (RPCs) operated in streamer mode and equipped with both digital and analog readout, providing the measurement of particle densities up to few particles per cm$^2$. The unique detector features (full coverage, readout granularity, wide dynamic range, etc) and location (very high altitude) allowed a detailed study of the lateral density profile of charged particles at ground very close to the shower axis and its description by a proper lateral distribution function (LDF). In particular, the information collected in the first 10 m from the shower axis have been shown to provide a very effective tool for the determination of the shower development stage ("age") in the energy range 50 TeV - 10 PeV. The sensitivity of the age parameter to the mass composition of primary Cosmic Rays is also discussed.
- Searching for new Higgs particle beyond the observed light Higgs boson h(125GeV) will unambiguously point to new physics beyond the standard model. We study the resonant production of a CP-even heavy Higgs state $H^0$ in the di-Higgs channel via, $gg\to H^0\to h^0h^0\to WW^*WW^*$, at the LHC Run-2 and the high luminosity LHC (HL-LHC). We analyze two types of the $4W$ decay modes, one with the same signed di-leptons ($4W\to\ell^\pm\nu\ell^\pm\nu 4q$) and the other with tri-leptons ($4W\to\ell^\pm\nu\ell^\mp\nu\ell^\pm\nu 2q$). We perform a full simulation for the signals and backgrounds, and estimate the discovery potential of the heavy Higgs state at the LHC Run-2 and the HL-LHC, in the context of generical two-Higgs-doublet models (2HDM). We determine the viable parameter space of the 2HDM as allowed by the theoretical constraints and the current experimental limits. We systematically analyze the allowed parameter space of the 2HDM which can be effectively probed by the heavy Higgs searches of the LHC, and further compare this with the viable parameter region under the current theoretical and experimental bounds.
- The next-generation lepton colliders, such as CEPC, FCC-ee, and ILC will make precision measurement of the Higgs boson properties. We first extract the Higgs coupling precision from Higgs observables at CEPC to illustrate the potential of future lepton colliders. Depending on the related event rates, the precision can reach percentage level for most couplings. Then, we try to estimate the new physics scales that can be indirectly probed with Higgs and electroweak precision observables. The Higgs observables, together with the existing electroweak precision observables, can probe new physics up to 10TeV (40TeV for the gluon-related operator $\mathcal O_g$) at 95% C.L. Including the $Z/W$ mass measurements and $Z$-pole observables at CEPC further pushes the limit up to 35TeV. Although $Z$-pole running is originally for the purpose of machine calibration, it can be as important as the Higgs observables for probing the new physics scales indirectly. The indirect probe of new physics scales at lepton colliders can mainly cover the energy range to be explored by the following hadron colliders of pp (50-100TeV), such as SPPC and FCC-hh.
- The DAMA/LIBRA experiment ($\sim$ 250 kg of highly radio-pure NaI(Tl)) is running deep underground at the Gran Sasso National Laboratory (LNGS) of the I.N.F.N. Here we briefly recall the results obtained in its first phase of measurements (DAMA/LIBRA--phase1, total exposure: 1.04 ton $\times$ yr). DAMA/LIBRA--phase1 and the former DAMA/NaI (cumulative exposure: $1.33$ ton $\times$ yr) give evidence at 9.3 $\sigma$ C.L. for the presence of DM particles in the galactic halo by exploiting the model-independent DM annual modulation signature. No systematic or side reaction able to mimic the exploited DM signature has been found or suggested by anyone over more than a decade. At present DAMA/LIBRA--phase2 is running with increased sensitivity.
- We report the results of searches for solar axions and galactic dark matter axions or axion-like particles with CDEX-1 experiment at the China Jinping Underground Laboratory, using 335.6 kg-days of data from a p-type point-contact germanium detector. The data are compatible with the background model and no excess signals are observed. Limits of solar axions on the model independent coupling $g_{Ae}<2.5\times10^{-11}$ from Compton, bremsstrahlung, atomic-recombination and deexcitation channel and $g^{\text{eff}}_{AN}\times g_{Ae}<6.1\times10^{-17}$ from $^{57}$Fe M1 transition at 90 % confidence level are derived. Within the framework of the DFSZ and KSVZ models, our results exclude the axion mass heavier than 0.9 eV/c$^{2}$ and 173 eV/c$^{2}$, respectively. The derived constraints for dark matter axions below 1 keV improves over the previous results.
- Leptonic unitarity triangle (LUT) provides fundamental means to geometrically describe CP violation in neutrino oscillation. In this work, we use LUT to present a new geometrical interpretation of the vacuum oscillation probability, and derive a compact new oscillation formula in terms of only 3 independent parameters of the corresponding LUT. Then, we systematically study matter effects in the geometrical formulation of neutrino oscillation with CP violation. Including nontrivial matter effects, we derive a very compact new oscillation formula by using the LUT formulation. We further demonstrate that this geometrical formula holds well for applications to neutrino oscillations in matter, including the long baseline experiments T2K, MINOS, NOvA, and DUNE.
- New physics beyond the standard model (SM) can be model-independently formulated via dimension-6 effective operators, whose coefficients (cutoffs) characterize the scales of new physics. We study the probe of new physics scales from the electroweak precision observables (EWPO) and the Higgs observables (HO) at the future $e^+e^-$ Higgs factory (such as CEPC). To optimize constraints of new physics from all available observables, we establish a scheme-independent approach. With this formulation, we treat the SM electroweak parameters and the coefficients of dimension-6 operators on equal footing, which can be fitted simultaneously by the same $\chi^2$ function. As deviations from the SM are generally small, we can expand the new physics parameters up to linear order and perform an analytical $\chi^2$ fit to derive the potential reach of the new physics scales. We find that the HO from both Higgs produnction and decay rates can probe the new physics scales up to 10TeV (and to 44TeV for the case of gluon-involved operator $\mathcal{O}_g$), and the new physics scales of Yukawa-type operators can be probed by the precision Higgs coupling measurements up to (13-25)TeV. Further including the EWPO can push the limit up to 35TeV. From this prospect, we demonstrate that the EWPO measured in the early phase of a Higgs factory can be as important as the Higgs observables. These indirect probes of new physics scales at the Higgs factory can mainly cover the energy range to be directly explored by the next generation hadron colliders of pp(50-100TeV), such as the SPPC and FCC-hh.
- LHC Run-2 has provided intriguing di-photon signals of a new resonance around 750GeV, which, if not due to statistical fluctuations, must call for new physics beyond the standard model (SM) at TeV scale. We propose a minimal extension of the SM with a complex singlet scalar $\mathcal{S}$ and a doublet of vector-like quarks. The scalar sector respects CP symmetry, with its CP-odd imaginary component $\chi$ providing a natural dark matter (DM) candidate. The real component of $\mathcal{S}$ serves as the new resonance (750GeV) and explains the diphoton excess of the LHC Run-2. The new scalar degrees of freedom of $\mathcal{S}$ help to stabilize the Higgs vacuum, and can realize the Higgs inflation around GUT scale, consistent with the current cosmology observations. We construct two representative samples A and B of our model for demonstration. We study the mono-jet signals of the DM production from invisible decays Re$(\mathcal{S}) \to \chi\chi$ at the LHC Run-2. We further derive the DM relic density bound, and analyze the constraints from direct and indirect DM detections.
- Jan 19 2016 hep-ex physics.ins-det arXiv:1601.04581v1The CDEX-1 experiment conducted a search of low-mass (< 10 GeV/c2) Weakly Interacting Massive Particles (WIMPs) dark matter at the China Jinping Underground Laboratory using a p-type point-contact germanium detector with a fiducial mass of 915 g at a physics analysis threshold of 475 eVee. We report the hardware set-up, detector characterization, data acquisition and analysis procedures of this experiment. No excess of unidentified events are observed after subtraction of known background. Using 335.6 kg-days of data, exclusion constraints on the WIMP-nucleon spin-independent and spin-dependent couplings are derived.
- The LHC discovery of a light Higgs particle $h^0$ (125GeV) opens up new prospect for searching heavier Higgs boson(s) at the LHC Run-2, which will unambiguously point to new physics beyond the standard model (SM). We study the detection of a heavier neutral Higgs boson $H^0$ via di-Higgs production channel at the LHC (14TeV), $H^0 \to h^0h^0 \to WW^*\gamma\gamma$. This directly probes the $Hhh$ cubic Higgs interaction, which exists in most extensions of the SM Higgs sector. For the decay products of final states $WW^*$, we include both pure leptonic mode $WW^* \to \ell\bar{\nu}\bar{\ell}\nu$ and semi-leptonic mode $WW^* \to q\bar{q}'\ell\nu$. We analyze signals and backgrounds by performing fast detector simulation for the full processes $pp \to H \to hh \to WW^*\gamma\gamma \to \ell\bar{\nu}\bar{\ell}\nu\gamma\gamma$ and $pp \to H \to hh \to WW^*\gamma\gamma \to \ell\nu q\bar{q}'\gamma\gamma$, over the mass range $M_H=250-600$GeV. For generic two-Higgs-doublet models (2HDM), we present the discovery reach of the heavier Higgs boson at the LHC Run-2, and compare it with the current Higgs global fit of the 2HDM parameter space.
- Despite the discovery of a Higgs boson h(125GeV) at the LHC Run-1, its self-interaction has fully evaded direct experimental probe so far. Such self-interaction is vital for electroweak symmetry breaking, vacuum stability and electroweak phase transition, and Higgs inflation. It is a most likely place to encode new physics beyond the standard model. We parametrize such new physics by model-independent dimension-6 effective operators, and study their tests via Higgs pair production at hadron colliders. We analyze three major di-Higgs production channels at parton level, and compare the parameter-dependence of total cross sections and kinematic distributions at the LHC(14TeV) and pp(100TeV) hadron collider. We further perform full simulations for the di-Higgs production channel $gg\to hh \to b\bar{b}\gamma\gamma$ and its backgrounds at the pp(100TeV) hadron collider. We construct four kinds of benchmark points, and study the sensitivities to probing different regions of the parameter space of cubic Higgs interactions. We find that for one-parameter analysis and with a 3/ab (30/ab) integrated luminosity, the $gg\to hh \to b\bar{b}\gamma\gamma$ channel can measure the SM cubic Higgs coupling and the derivative cubic Higgs coupling to an accuracy of about 13% (4.2%) and 5% (1.6%), respectively.
- In the present paper the results obtained in the investigation of possible diurnal effects for low-energy single-hit scintillation events of DAMA/LIBRA-phase1 (1.04 ton $\times$ yr exposure) have been analysed in terms of an effect expected in case of Dark Matter (DM) candidates inducing nuclear recoils and having high cross-section with ordinary matter, which implies low DM local density in order to fulfill the DAMA/LIBRA DM annual modulation results. This effect is due to the different Earth depths crossed by those DM candidates during the sidereal day.
- Mar 25 2015 hep-ex astro-ph.HE arXiv:1503.07136v1The ARGO-YBJ experiment is a full-coverage air shower detector located at the Yangbajing Cosmic Ray Observatory (Tibet, People's Republic of China, 4300 m a.s.l.). The high altitude, combined with the full-coverage technique, allows the detection of extensive air showers in a wide energy range and offer the possibility of measuring the cosmic ray proton plus helium spectrum down to the TeV region, where direct balloon/space-borne measurements are available. The detector has been in stable data taking in its full configuration from November 2007 to February 2013. In this paper the measurement of the cosmic ray proton plus helium energy spectrum is presented in the region 3-300 TeV by analyzing the full collected data sample. The resulting spectral index is $\gamma = -2.64 \pm 0.01$. These results demonstrate the possibility of performing an accurate measurement of the spectrum of light elements with a ground based air shower detector.
- Feb 12 2015 astro-ph.HE hep-ex arXiv:1502.03164v1The measurement of cosmic ray energy spectra, in particular for individual species, is an essential approach in finding their origin. Locating the "knees" of the spectra is an important part of the approach and has yet to be achieved. Here we report a measurement of the mixed Hydrogen and Helium spectrum using the combination of the ARGO-YBJ experiment and of a prototype Cherenkov telescope for the LHAASO experiment. A knee feature at 640+/-87 TeV, with a clear steepening of the spectrum, is observed. This gives fundamental inputs to galactic cosmic ray acceleration models.
- So far all evidences of dark matter (DM) come from astrophysical and cosmological observations, due to gravitational interactions of the DM. It is possible that the true DM particle in the universe joins gravitational interactions only, but nothing else. Such a Gravitational DM (GDM) acts as a weakly interacting massive particle (WIMP), which is conceptually simple and attractive. In this work, we explore this direction by constructing the simplest scalar GDM particle $\chi_s$. It is a $Z_2$ odd singlet under the standard model (SM) gauge group, and naturally joins the unique dimension-4 interaction with Ricci curvature, $\xi_s \chi_s^2 R$, where $\xi_s$ is the dimensionless nonminimal coupling. We demonstrate that this gravitational interaction $\xi_s \chi_s^2 R$, together with Higgs-curvature nonminimal coupling term $\xi_h H^\dag H R$, induces effective couplings between $\chi_s^2$ and SM fields which can account for the observed DM thermal relic abundance. We analyze the annihilation cross sections of GDM particles and derive the viable parameter space for realizing the DM thermal relic density. We further study the direct/indirect detections and the collider signatures of such a scalar GDM. These turn out to be highly predictive and testable.
- This paper summarizes in a simple and intuitive way why the neutrons, the muons and the solar neutrinos cannot give any significant contribution to the DAMA annual modulation results. A number of these elements have already been presented in individual papers; they are recalled here. Afterwards, few simple considerations are summarized which already demonstrate the incorrectness of the claim reported in PRL 113 (2014) 081302.
- The recent IceCube observation of ultra-high-energy astrophysical neutrinos has begun the era of neutrino astronomy. In this work, using the unitarity of leptonic mixing matrix, we derive nontrivial unitarity constraints on the flavor composition of astrophysical neutrinos detected by IceCube. Applying leptonic unitarity triangles, we deduce these unitarity bounds from geometrical conditions, such as triangular inequalities. These new bounds generally hold for three flavor neutrinos, and are independent of any experimental input or the pattern of leptonic mixing. We apply our unitarity bounds to derive general constraints on the flavor compositions for three types of astrophysical neutrino sources (and their general mixture), and compare them with the IceCube measurements. Furthermore, we prove that for any sources without $\nu_\tau$ neutrinos, a detected $\nu_\mu$ flux ratio $< 1/4$ will require the initial flavor composition with more $\nu_e$ neutrinos than $\nu_\mu$ neutrinos.
- Higgs inflation is among the most economical and predictive inflation models, although the original Higgs inflation requires tuning the Higgs or top mass away from its current experimental value by more than $2\sigma$ deviations, and generally gives a negligible tensor-to-scalar ratio $r \sim 10^{-3}$ (if away from the vicinity of critical point). In this work, we construct a minimal extension of Higgs inflation, by adding only two new weak-singlet particles at TeV scale, a vector-quark $T$ and a real scalar $S$. The presence of singlets $(T, S)$ significantly impact the renormalization group running of the Higgs boson self-coupling. With this, our model provides a wider range of the tensor-to-scalar ratio $r = O(0.1 - 10^{-3})$, consistent with the favored $r$ values by either BICEP2 or Planck data, while keeping the successful prediction of the spectral index $ n_s \simeq 0.96 $. It further allows the Higgs and top masses to fully fit the collider measurements. We also discuss implications for searching the predicted TeV-scale vector-quark $T$ and scalar $S$ at the LHC and future high energy pp colliders.
- Apr 22 2014 hep-ex physics.ins-det arXiv:1404.4946v2We report results of a search for light Dark Matter WIMPs with CDEX-1 experiment at the China Jinping Underground Laboratory, based on 53.9 kg-days of data from a p-type point-contact germanium detector enclosed by a NaI(Tl) crystal scintillator as anti-Compton detector. The event rate and spectrum above the analysis threshold of 475 eVee are consistent with the understood background model. Part of the allowed regions for WIMP-nucleus coherent elastic scattering at WIMP mass of 6-20 GeV are probed and excluded. Independent of interaction channels, this result contradicts the interpretation that the anomalous excesses of the CoGeNT experiment are induced by Dark Matter, since identical detector techniques are used in both experiments.
- The China Dark Matter Experiment reports results on light WIMP dark matter searches at the China Jinping Underground Laboratory with a germanium detector array with a total mass of 20 g. The physics threshold achieved is 177 eVee ("ee" represents electron equivalent energy) at 50% signal efficiency. With 0.784 kg-days of data, exclusion region on spin-independent coupling with the nucleon is derived, improving over our earlier bounds at WIMP mass less than 4.6 GeV.
- The results obtained in the search for possible diurnal effect in the single-hit low energy data collected by DAMA/LIBRA-phase1 (total exposure: 1.04 ton x yr) deep underground at the Gran Sasso National Laboratory (LNGS) of the I.N.F.N. are presented. At the present level of sensitivity the presence of any significant diurnal variation and of diurnal time structures in the data can be excluded for both the cases of solar and sidereal time. In particular, the diurnal modulation amplitude expected, because of the Earth diurnal motion, on the basis of the DAMA Dark Matter annual modulation results is below the present sensitivity.
- Mar 07 2014 physics.ins-det hep-ex arXiv:1403.1404v1The DAMA/LIBRA experiment is composed by about 250 kg of highly radiopure NaI(Tl). It is in operation at the underground Gran Sasso National Laboratory of the INFN. The main aim of the experiment is to investigate the Dark Matter (DM) particles in the Galactic halo by exploiting the model independent DM annual modulation signature. The DAMA/LIBRA experiment and the former DAMA/NaI (the first generation experiment having an exposed mass of about 100 kg) have released results corresponding to a total exposure of 1.17 ton $\times$ yr over 13 annual cycles; they have provided a model independent evidence of the presence of DM particles in the galactic halo at 8.9 $\sigma$ C.L.. The results of a further annual cycle, concluding the DAMA/LIBRA--phase1, have been released after this Workshop and are not included here. In the fall 2010 an important upgrade of the experiment have been performed. All the PMTs of the NaI(Tl) detectors have been replaced with new ones having higher quantum efficiency with the aim to decrease the software energy threshold considered in the data analysis. The perspectives of the running DAMA/LIBRA--phase2 will be shortly summarized.
- Jan 28 2014 astro-ph.HE hep-ex arXiv:1401.6987v2The energy spectrum of cosmic Hydrogen and Helium nuclei has been measured, below the so-called "knee", by using a hybrid experiment with a wide field-of-view Cherenkov telescope and the Resistive Plate Chamber (RPC) array of the ARGO-YBJ experiment at 4300 m above sea level. The Hydrogen and Helium nuclei have been well separated from other cosmic ray components by using a multi-parameter technique. A highly uniform energy resolution of about 25% is achieved throughout the whole energy range (100 TeV - 700 TeV). The observed energy spectrum is compatible with a single power law with index gamma=-2.63+/-0.06.
- Leptonic unitarity triangle (LUT) provides a geometric description of CP violations in the lepton-neutrino sector and is directly measurable in principle. In this work, we reveal that the angles in the LUT have definite physical meaning, and demonstrate the exact connection of the LUT to neutrino oscillations. For the first time, we prove that these leptonic angles act as phase shifts in neutrino oscillations, by shifting ∆m^2L/2E to ∆m^2L/2E + \alpha, where (L, E, \alpha) denote the baseline length, neutrino energy and corresponding angle of the LUT. Each LUT has three independent parameters and contains only partial information of the PMNS matrix. We demonstrate that the partial information in each LUT can describe the corresponding neutrino oscillation. Hence, for the first time, we uncover that any given kind of neutrino oscillations contain at most three (rather than four) independent degrees of freedom from the PMNS matrix. This may provide a cleaner way for fitting the corresponding oscillation data.
- The discovery by the ATLAS and CMS experiments of a new boson with mass around 125 GeV and with measured properties compatible with those of a Standard-Model Higgs boson, coupled with the absence of discoveries of phenomena beyond the Standard Model at the TeV scale, has triggered interest in ideas for future Higgs factories. A new circular e+e- collider hosted in a 80 to 100 km tunnel, TLEP, is among the most attractive solutions proposed so far. It has a clean experimental environment, produces high luminosity for top-quark, Higgs boson, W and Z studies, accommodates multiple detectors, and can reach energies up to the t-tbar threshold and beyond. It will enable measurements of the Higgs boson properties and of Electroweak Symmetry-Breaking (EWSB) parameters with unequalled precision, offering exploration of physics beyond the Standard Model in the multi-TeV range. Moreover, being the natural precursor of the VHE-LHC, a 100 TeV hadron machine in the same tunnel, it builds up a long-term vision for particle physics. Altogether, the combination of TLEP and the VHE-LHC offers, for a great cost effectiveness, the best precision and the best search reach of all options presently on the market. This paper presents a first appraisal of the salient features of the TLEP physics potential, to serve as a baseline for a more extensive design study.
- Aug 26 2013 astro-ph.GA hep-ex arXiv:1308.5109v2The results obtained with the total exposure of 1.04 ton x yr collected by DAMA/LIBRA-phase1 deep underground at the Gran Sasso National Laboratory (LNGS) of the I.N.F.N. during 7 annual cycles (i.e. adding a further 0.17 ton x yr exposure) are presented. The DAMA/LIBRA-phase1 data give evidence for the presence of Dark Matter (DM) particles in the galactic halo, on the basis of the exploited model independent DM annual modulation signature by using highly radio-pure NaI(Tl) target, at 7.5 sigma C.L.. Including also the first generation DAMA/NaI experiment (cumulative exposure 1.33 ton x yr, corresponding to 14 annual cycles), the C.L. is 9.3 sigma and the modulation amplitude of the single-hit events in the (2-6) keV energy interval is: (0.0112 \pm 0.0012) cpd/kg/keV; the measured phase is (144 \pm 7) days and the measured period is (0.998 \pm 0.002) yr, values well in agreement with those expected for DM particles. No systematic or side reaction able to mimic the exploited DM signature has been found or suggested by anyone over more than a decade.
- We construct a minimal viable extension of the standard model (SM) with classical scale symmetry. Its scalar sector contains a complex singlet in addition to the SM Higgs doublet. The scale-invariant and CP-symmetric Higgs potential generates radiative electroweak symmetry breaking a la Coleman-Weinberg, and gives a natural solution to the hierarchy problem, free from fine-tuning. Besides the 125GeV SM-like Higgs particle, it predicts a new CP-even Higgs (serving as the pseudo-Nambu-Goldstone boson of scale symmetry breaking) and a CP-odd scalar singlet (providing the dark matter candidate) at weak scale. We systematically analyze experimental constraints from direct LHC Higgs searches and electroweak precision tests, as well as theoretical bounds from unitarity, triviality and vacuum stability. We demonstrate the viable parameter space, and discuss implications for new Higgs and dark matter (DM) searches at the upcoming LHC runs and for the on-going direct detections of DM.
- The China Dark matter Experiment collaboration reports the first experimental limit on WIMP dark matter from 14.6 kg-day of data taken with a 994 g p-type point-contact germanium detector at the China Jinping underground Laboratory where the rock overburden is more than 2400 m. The energy threshold achieved was 400 eVee. According to the 14.6 kg-day live data, we placed the limit of N= 1.75 * 10^-40 cm^2 at 90% confidence level on the spin-independent cross-section at WIMP mass of 7 GeV before differentiating bulk signals from the surface backgrounds.
- With the LHC discovery of a 125 GeV Higgs-like boson, we study gravitational interaction of the Higgs boson via the unique dimension-4 operator involving Higgs doublet and scalar curvature, $\,\xi H^\dag H R\,$, with nonminimal coupling $\,\xi\,$. This Higgs portal term can be transformed away in Einstein frame and induces gauge-invariant effective interactions in the Higgs sector. We study the weak boson scattering in Einstein frame, and explicitly demonstrate the longitudinal-Goldstone boson equivalence theorem in the presence of $\,\xi\,$ coupling. With these, we derive unitarity bound on the Higgs gravitational coupling $\,\xi\,$ in Einstein frame, which is stronger than that inferred from the current LHC Higgs measurements. We further study $\xi$-dependent weak boson scattering cross sections at TeV scale, and propose a new LHC probe of the Higgs-gravity coupling $\,\xi\,$ via weak boson scattering experiments.
- We study LHC Higgs signatures from topflavor seesaw realization of electroweak symmetry breaking with a minimal gauge extension SU(2) x SU(2) x U(1). This elegant renormalizable construction singles out top quark sector (instead of all other light fermions) to join the new SU(2) gauge force. It predicts extra vector-like spectator quarks (T, B), new gauge bosons (W', Z'), and a pair of neutral Higgs bosons (h, H). We demonstrate that for the lighter Higgs boson h of mass 125GeV, this model predicts modified Higgs signal rates in h --> \gamma\gamma, WW*, ZZ* channels via gluon fusions, in h --> tau tau mode via vector boson fusions, and in h --> bb mode via gauge boson associate productions. We perform a global fit for our theory by including both direct search data (LHC and Tevatron) and indirect precision constraints. We further analyze the LHC discovery potential for detecting the heavier Higgs state H.
- A new hybrid experiment has been started by AS\gamma experiment at Tibet, China, since August 2011, which consists of a low threshold burst-detector-grid (YAC-II, Yangbajing Air shower Core array), the Tibet air-shower array (Tibet-III) and a large underground water Cherenkov muon detector (MD). In this paper, the capability of the measurement of the chemical components (proton, helium and iron) with use of the (Tibet-III+YAC-II) is investigated by means of an extensive Monte Carlo simulation in which the secondary particles are propagated through the (Tibet-III+YAC-II) array and an artificial neural network (ANN) method is applied for the primary mass separation. Our simulation shows that the new installation is powerful to study the chemical compositions, in particular, to obtain the primary energy spectrum of the major component at the knee.
- Weakly Interacting Massive Particles (WIMPs) are the candidates of dark matter in our universe. Up to now any direct interaction of WIMP with nuclei has not been observed yet. The exclusion limits of the spin-independent cross section of WIMP-nucleon which have been experimentally obtained is about 10^-7pb at high mass region and only 10^-5pb at low mass region. China Jin-Ping underground laboratory CJPL is the deepest underground lab in the world and provides a very promising environment for direct observation of dark matter. The China Dark Matter Experiment (CDEX) experiment is going to directly detect the WIMP flux with high sensitivity in the low mass region. Both CJPL and CDEX have achieved a remarkable progress in recent two years. The CDEX employs a point-contact germanium semi-conductor detector PCGe whose detection threshold is less than 300 eV. We report the measurement results of Muon flux, monitoring of radioactivity and Radon concentration carried out in CJPL, as well describe the structure and performance of the 1 kg PCGe detector CDEX-1 and 10kg detector array CDEX-10 including the detectors, electronics, shielding and cooling systems. Finally we discuss the physics goals of the CDEX-1, CDEX-10 and the future CDEX-1T detectors.
- Theories of quantum gravity predict spacetime dimensions to become reduced at high energies, a striking phenomenon known as spontaneous dimensional reduction (SDR). We construct an effective electroweak theory based on the standard model (SM) and incorporate the TeV-scale SDR, which exhibits good high energy behavior and ensures the unitarity of weak gauge boson scattering. This also provides a natural solution to the hierarchy problem in the presence of scalar Higgs boson. We demonstrate that this model predicts unitary longitudinal weak boson scattering, and can be discriminated from the conventional 4d SM by the WW scattering experiments at the CERN LHC.
- We study LHC Higgs signatures from the extended electroweak gauge symmetry SU(2) x SU(2) x U(1). Under this gauge structure, we present an effective UV completion of the 3-site moose model with ideal fermion delocalization, which contains two neutral Higgs states (h, H) and three new gauge bosons (W', Z'). We study the unitarity, and reveal that the exact E^2 cancellation in the longitudinal WW scattering amplitudes is achieved by the joint role of exchanging both spin-1 new gauge bosons and spin-0 Higgs bosons. We identify the lighter Higgs state h with mass 125GeV, and derive the unitarity bound on the mass of heavier Higgs boson H. The parameter space of this model is highly predictive. We study the production and decay signals of this 125GeV Higgs boson h at the LHC. We demonstrate that the h Higgs boson can naturally have enhanced signals in the diphoton channel $gg \to h \to\gamma\gamma$, while the events rates in the reactions $gg \to h \to WW^*$ and $gg \to h \to ZZ^*$ are generally suppressed relative to the SM expectation. Searching the h Higgs boson via associated productions and vector boson fusions are also discussed for our model. We further analyze the LHC signals of the heavier Higgs boson H as a distinctive new physics discriminator from the SM. For wide mass-ranges of H, we derive constraints from the existing LHC searches, and study the discovery potential of H at the LHC(8TeV) and LHC(14TeV).
- We study the physics potential of the 8TeV LHC (LHC-8) to discover, during its 2012 run, a large class of extended gauge models or extra dimensional models whose low energy behavior is well represented by an SU(2)^2 x U(1) gauge structure. We analyze this class of models and find that with a combined integrated luminosity of 40-60/fb at the LHC-8, the first new Kaluza-Klein mode of the W gauge boson can be discovered up to a mass of about 370-400 GeV, when produced in association with a Z boson.
- We propose octahedral group O_h as the family symmetry of neutrino-lepton sector. We find that O_h contains subgroups Z_2(mu-tau) x Z_2(solar) and Z_4^l for realizing the bimaximal (BM) mixings, theta_23 = theta_12 = 45^o and theta_13=0^o, where Z_2(mu-tau) x Z_2(solar) and Z_4^l serve as the residual symmetries of neutrinos and charged leptons, respectively. We present geometric interpretations of BM mixing in the octahedron, and construct natural geometrical breaking of Z_4^l, leading to nontrivial deviations from the BM mixings. Our theory makes truly simple predictions of a relatively large reactor angle, theta_13 = 45^o - theta_12 = 7.5^o - 13.7^o (3 sigma), the nearly maximal atmospheric angle and the approximate maximal Dirac CP violation. These agree well with the current neutrino data, and will be further probed by the on-going and upcoming oscillation experiments.
- Mirror universe is a fundamental way to restore parity symmetry in weak interactions. It naturally provides the lightest mirror nucleon as a unique GeV-scale asymmetric dark matter particle candidate. We conjecture that the mirror parity is respected by the fundamental interaction Lagrangian, and its possible soft breaking arises only from non-interaction terms in the gauge-singlet sector. We realize the spontaneous mirror parity violation by minimizing the vacuum Higgs potential, and derive the corresponding Higgs spectrum. We demonstrate that the common origin of CP violation in the visible and mirror neutrino seesaws can generate the right amount of matter and mirror dark matter via leptogenesis. We analyze the direct detections of GeV-scale mirror dark matter by TEXONO and CDEX experiments. We further study the predicted distinctive Higgs signatures at the LHC.
- This paper gathers arguments and reasons why muons surviving the Gran Sasso mountain cannot mimic the Dark Matter annual modulation signature exploited by the DAMA/NaI and DAMA/LIBRA experiments. A number of these items have already been presented in individual papers. Further arguments have been addressed here in order to present a comprehensive collection and to enable a wider community to correctly approach this point.
- On-going Higgs searches in the light mass window are of vital importance for testing the Higgs mechanism and probing new physics beyond the standard model (SM). The latest ATLAS and CMS searches for the SM Higgs boson at the LHC (7TeV) found some intriguing excesses of events in the \gamma\gamma/VV^* channels (V=Z,W) around the mass-range of 124-126 GeV. We explore a possible explanation of the \gamma\gamma and VV^* signals from the light CP-odd Higgs A^0 or CP-even Higgs h^0 from the general two-Higgs-doublet model with fourth-family fermions. We demonstrate that by including invisible decays of the Higgs boson A^0 or h^0 to fourth-family neutrinos, the predicted \gamma\gamma and VV^* signals can explain the observed new signatures at the LHC, and will be further probed by the forthcoming LHC runs in 2012.
- Spontaneous dimensional reduction (SDR) is a striking phenomenon predicted by a number of quantum gravity approaches which all indicate that the spacetime dimensions get reduced at high energies. In this work, we formulate an effective theory of electroweak interactions based upon the standard model, incorporating the spontaneous reduction of space-dimensions at TeV scale. The electroweak gauge symmetry is nonlinearly realized with or without a Higgs boson. We demonstrate that the SDR ensures good high energy behavior and predicts unitary weak boson scattering. For a light Higgs boson of mass 125GeV, the TeV-scale SDR gives a natural solution to the hierarchy problem. Such a light Higgs boson can have induced anomalous gauge couplings from the TeV-scale SDR. We find that the corresponding WW scattering cross sections become unitary at TeV scale, but exhibit different behaviors from that of the 4d standard model. These can be discriminated by the WW scattering experiments at the LHC.
- Existence of a mirror world in the universe is a fundamental way to restore the observed parity violation in weak interactions and provides the lightest mirror nucleon as a unique GeV-scale dark matter particle candidate. The visible and mirror worlds share the same spacetime of the universe and are connected by a unique space-inversion symmetry -- the mirror parity (P). We conjecture that the mirror parity is respected by the fundamental interaction Lagrangian, and study its spontaneous breaking from minimizing the Higgs vacuum potential. The domain wall problem is resolved by a unique soft breaking linear-term from the P-odd weak-singlet Higgs field. We also derive constraint from the Big-Bang nucleosynthesis. We then analyze the neutrino seesaw for both visible and mirror worlds, and demonstrate that the desired amounts of visible matter and mirror dark matter in the universe arise from a common origin of CP violation in the neutrino sector via leptogenesis. We derive the Higgs mass-spectrum and Higgs couplings with gauge bosons and fermions. We show their consistency with the direct Higgs searches and the indirect precision constraints. We further study the distinctive signatures of the predicted non-standard Higgs bosons at the LHC. Finally, we analyze the direct detections of GeV-scale mirror dark matter by TEXONO and CDEX experiments.
- We conjecture that all CP violations (both Dirac and Majorana types) arise from a common origin in neutrino seesaw. With this conceptually attractive and simple conjecture, we deduce that mu-tau breaking shares the common origin with all CP violations. We study the common origin of mu-tau and CP breaking in the Dirac mass matrix of seesaw Lagrangian (with right-handed neutrinos being mu-tau blind), which uniquely leads to inverted mass-ordering of light neutrinos. We then predict a very different correlation between the two small mu-tau breaking observables theta_13-0 and theta_23-45, which can saturate the present experimental upper limit on theta_13. This will be tested against our previous normal mass-ordering scheme by the on-going oscillation experiments. We also analyze the correlations of theta_13 with Jarlskog invariant and neutrinoless double-beta-decay observable. From the common origin of CP and mu-tau breaking in the neutrino seesaw, we establish a direct link between the low energy CP violations and the cosmological CP violation for baryon asymmetry. With these we further predict a lower bound on theta_13, supporting the on-going probes of theta_13 at Daya Bay, Double Chooz and RENO experiments. Finally, we analyze the general model-independent Z_2 x Z_2 symmetry structure of the light neutrino sector, and map it into the seesaw sector, where one of the Z_2's corresponds to the mu-tau symmetry and another the hidden symmetry Z_2^s (revealed in our previous work) which dictates the solar mixing angle \theta_12. We derive the physical consequences of this Z_2^s and its possible partial violation in the presence of mu-tau breaking (without or with neutrino seesaw), regarding the theta_12 determination and the correlation between mu-tau breaking observables.
- The sun blocks cosmic ray particles from outside the solar system, forming a detectable shadow in the sky map of cosmic rays detected by the ARGO-YBJ experiment in Tibet. Because the cosmic ray particles are positive charged, the magnetic field between the sun and the earth deflects them from straight trajectories and results in a shift of the shadow from the true location of the sun. Here we show that the shift measures the intensity of the field which is transported by the solar wind from the sun to the earth.
- A search for the production and non-standard decay of a Higgs boson, h, into four taus through intermediate pseudoscalars, a, is conducted on 683 pb-1 of data collected by the ALEPH experiment at centre-of-mass energies from 183 to 209 GeV. No excess of events above background is observed, and exclusion limits are placed on the combined production cross section times branching ratio, \xi^2 = \sigma(e+e- --> Zh)/\sigma_SM(e+e- --> Zh) x B(h --> aa)x B(a --> \tau^+\tau^-)^2. For mh < 107 GeV/c2 and 4 < ma < 10 GeV/c2, \xi^2 > 1 is excluded at the 95% confidence level.
- DAMA/LIBRA is running at the Gran Sasso National Laboratory of the I.N.F.N.. Here the results obtained with a further exposure of 0.34 ton x yr are presented. They refer to two further annual cycles collected one before and one after the first DAMA/LIBRA upgrade occurred on September/October 2008. The cumulative exposure with those previously released by the former DAMA/NaI and by DAMA/LIBRA is now 1.17 ton x yr, corresponding to 13 annual cycles. The data further confirm the model independent evidence of the presence of Dark Matter (DM) particles in the galactic halo on the basis of the DM annual modulation signature (8.9 sigma C.L. for the cumulative exposure). In particular, with the cumulative exposure the modulation amplitude of the single-hit events in the (2 -- 6) keV energy interval measured in NaI(Tl) target is (0.0116 +- 0.0013) cpd/kg/keV; the measured phase is (146 +- 7) days and the measured period is (0.999 +- 0.002) yr, values well in agreement with those expected for the DM particles.
- A variety of detectors has been proposed for dark matter direct detection, but most of them -- by the fact -- are still at R&D stage. In many cases, it is claimed that the lack of an adequate detectors' radio-purity might be compensated through heavy uses of MonteCarlo simulations, subtractions and handlings of the measured counting rates, in order to claim higher sensitivity (just for a particular scenario). The relevance of a correct evaluation of systematic effects in the use of MonteCarlo simulations at very low energy (which has always been safely discouraged in the field so far) and of multiple subtractions and handling procedures applied to the measured counting rate is shortly addressed here at some extent. Many other aspects would also deserve suitably deep investigations.
- May 13 2009 hep-ex arXiv:0905.1784v1A tau lepton can be produced in a charged current interaction by cosmic ray tau neutrino with material inside a mountain. If it escapes from the mountain, it will decay and initiate a shower in the air, which can be detected by an air shower fluorescence/Cherenkov light detector. Designed according to such a principle, the Cosmic Ray Tau Neutrino Telescope (CRTNT) experiment, located at the foothill of Mt. Balikun in Xinjiang, China, will search for very high-energy cosmic tau neutrinos from energetic astrophysical sources by detecting those showers. This paper describes a Monte Carlo simulation for a detection of tau neutrino events by the CRTNT experiment. Ultra-high-energy cosmic ray events are also simulated to estimate the potential contamination. With the CRTNT experiment composed of four detector stations, each covering 64 by 14 degrees field of view, the expected event rates are 28.6, 21.9 and 4.7 per year assuming AGN neutrino flux according to Semikoz et. al. 2004, MPR AGN jet model and SDSS AGN core model, respectively. Null detection of such tau event by the CRTNT experiment in one year could set 90% C.L. upper limit at 19.9 (eV^-1 cm^-2 s^-1 sr^-1) for E^-2 neutrino spectrum.
- We study the LHC signatures of new gauge bosons in the gauge-invariant minimal Higgsless model. It predicts an extra pair of W_1 and Z_1 bosons which can be as light as ~400GeV and play a key role in the delay of unitarity violation. We analyze the W_1 signals in pp --> W_0Z_0Z_0 --> jj4\ell and pp --> jj W_0Z_0 --> jj3\ell\nu processes at the LHC, including the complete electroweak and QCD backgrounds. We reveal the complementarity between these two channels for discovering the W_1 boson, and demonstrate the LHC discovery potential over the full range of allowed W_1 mass.
- We analyze the spectrum and properties of a highly-deconstructed Higgsless model with only three sites. Such a model contains sufficient complexity to incorporate interesting physics issues related to fermion masses and electroweak observables, yet remains simple enough that it could be encoded in a Matrix Element Generator program for use with Monte Carlo simulations. The gauge sector of this model is equivalent to that of the BESS model; the new physics of interest here lies in the fermion sector. We analyze the form of the fermion Yukawa couplings required to produce the ideal fermion delocalization that causes tree-level precision electroweak corrections to vanish. We discuss the size of one-loop corrections to b \to s \gamma, the weak-isospin violating parameter \alpha T and the decay Z \to b \barb. We find that the new fermiophobic vector states (the analogs of the gauge-boson KK modes in a continuum model) can be reasonably light, with a mass as low as 380 GeV, while the extra (approximately vectorial) quark and lepton states (the analogs of the fermion KK modes) must be heavier than 1.8 TeV.
- We study 2 --> n inelastic fermion-(anti)fermion scattering into multiple longitudinal weak gauge bosons and derive universal upper bounds on the scales of fermion mass generation by imposing unitarity of the S-matrix. We place new upper limits on the scales of fermion mass generation, independent of the electroweak symmetry breaking scale. We find that the strongest 2 --> n limits fall in a narrow range, 3-170 TeV (with n=2-24), depending on the observed fermion masses.
- Deconstruction is a powerful means to explore the rich dynamics of gauge theories in four and higher dimensions. We demonstrate that gauge symmetry breaking in a compactified higher dimensional theory can be formulated via deconstructed 4D moose theory with \it spontaneous symmetry breaking and \it without boundary condition. The proper higher-D boundary conditions are automatically induced in the continuum limit rather than being imposed. We identify and analyze the moose theories which exhibit \it delayed unitarity violation (effective unitarity) as a \it collective effect of many gauge groups, without resorting to any known 5D geometry. Relevant phenomenological constraints are also addressed.
- Scales of mass generation for Majorana neutrinos (as well as quarks and leptons) can be probed from high energy 2 --> n inelastic scattering involving a multiple longitudinal gauge boson final state. We demonstrate that the unitarity of 2 --> n scattering puts the strongest new upper limit on the scale of fermion mass generation, independent of the electroweak symmetry breaking scale $v=(\sqrt{2}G_F)^{-1/2}$. Strikingly, for Majorana neutrinos (quarks and leptons), we find that the strongest 2 --> n limits fall in a narrow range, 136-170 TeV (3-107 TeV) with n=20-24 (n=2-12), depending on the observed fermion masses. Physical implications are discussed.
- The scale of mass generation for fermions (including neutrinos) and the scale for electroweak symmetry breaking (EWSB) can be bounded from above by the unitarity of scattering involving longitudinal weak gauge bosons or their corresponding would-be Goldstone bosons. Including the exact n-body phase space we analyze the 2 --> n ($n \geq 2$) processes for the fermion-(anti)fermion scattering into multiple gauge boson final states. Contrary to naive energy power counting, we demonstrate that as $n$ becomes large, the competition between an increasing energy factor and a phase-space suppression leads to a \it strong new upper bound on the scale of fermion mass generation at a finite value $n=n_s$, which is \it independent of the EWSB scale, $v = (\sqrt{2}G_F)^{-1/2}$. For quarks, leptons and Majorana neutrinos, the strongest 2 --> n limits range from about 3TeV to 130-170TeV (with $2\lesssim n_s \lesssim 24$), depending on the measured fermion masses. Strikingly, given the tiny neutrino masses as constrained by the neutrino oscillations, neutrinoless double-beta decays and astrophysical observations, the unitarity violation of $\nu_L\nu_L\to nW_L^a$ scattering actually occurs at a scale no higher than ~170 TeV. Implications for various mechanisms of neutrino mass generation are analyzed. On the other hand, for the 2 --> n pure Goldstone-boson scattering, we find that the decreasing phase space factor always dominates over the growing overall energy factor when $n$ becomes large, so that the best unitarity bound on the scale of EWSB remains at n=2.
- Recently Barbieri, et al. have introduced a formalism to express the deviations of electroweak interactions from their standard model forms in "universal" theories, i.e. theories in which the corrections due to new physics can be expressed solely by modifications to the two-point correlation function of electroweak gauge currents of fermions. The parameters introduced by these authors are defined by the properties of the correlation functions at zero momentum, and differ from the quantities calculated by examining the on-shell properties of the electroweak gauge bosons. In this letter we discuss the relationship between the zero-momentum and on-shell parameters. In addition, we present the results of a calculation of these zero-momentum parameters in an arbitrary Higgsless model in which the low-energy rho parameter is one and which can be deconstructed to a linear chain of SU(2) groups adjacent to a chain of U(1) groups. Our results demonstrate the importance of the universal "non-oblique" corrections which are present and elucidate the relationships among various calculations of electroweak quantities in these models. Our expressions for these zero-momentum parameters depend only on the spectrum of heavy vector-boson masses; therefore, the minimum size of the deviations present in these models is related to the upper bound on the heavy vector-boson masses derived from unitarity. We find that these models are disfavored by precision electroweak data, independent of any assumptions about the background metric or the behavior of the bulk coupling.
- Unitarity of the 4d standard model is ensured by the conventional Higgs mechanism with a fundamental spin-0 Higgs boson, responsible for gauge boson mass-generations. On the contrary Kaluza-Klein (KK) compactification of extra spatial dimensions can geometrically realize the gauge boson mass generation without invoking a fundamental Higgs scalar. We reveal that massive gauge boson scattering in the compactified theories is unitary at low energies, and the unitarity violation is \it delayed to the intrinsic ultraviolet (UV) scale of the higher dimensional gauge theory. We demonstrate that this is a generic consequence of the ``geometric Higgs mechanism'' (GHM), manifested via Kaluza-Klein equivalence theorem (KK-ET). We further show that the presence of many gauge KK states below the UV cutoff scale imposes strong bounds on the highest KK level (N_KK). Applying these bounds to higher-dimensional SUSY GUTs implies that only a small number of KK states can be used to accelerate gauge coupling unification, and suggests that the GUT scale in the 5d minimal SUSY SU(5) is above 10^14 GeV.
- The ``Little Higgs'' opens up a new avenue for natural electroweak symmetry breaking in which the standard model Higgs particle is realized as a pseudo-Goldstone boson and thus is generically light. The symmetry breaking structure of the Little Higgs models predicts a large multiplet of (pseudo-)Goldstone bosons and their low energy interactions below the ultraviolet (UV) completion scale $\Lambda \sim 4\pi f \sim O(10)$ TeV, where $f$ is the Goldstone decay constant. We study unitarity of the Little Higgs models by systematically analyzing the high energy scatterings of these (pseudo-)Goldstone bosons. We reveal that the collective effect of the Goldstone scatterings via coupled channel analysis tends to push the unitarity violation scale $\Lambda_U$ significantly below the conventional UV scale $\Lambda \sim 4\pi f$ as estimated by naive dimensional analysis (NDA). Specifically, $\Lambda_U \sim (3-4)f$, lying in the multi-TeV range for $f\sim 1$ TeV. We interpret this as an encouraging sign that the upcoming LHC may explore aspects of Little Higgs UV completions, and we discuss some potential signatures. The meanings of the two estimated UV scales $\Lambda_U$ (from unitarity violation) and $\Lambda$ (from NDA) together with their implications for an effective field theory analysis of the Little Higgs models are also discussed.
- The cosmological matter-antimatter asymmetry can originate from CP-violating interactions of seesaw Majorana neutrinos via leptogenesis in the thermal phase of the early universe. Having the cosmological CP-phase for leptogenesis requires at least two right-handed Majorana neutrinos. Using only the low energy neutrino observables we quantitatively reconstruct a minimal neutrino seesaw. We establish a general criterion for minimal seesaw schemes in which the cosmological CP-phase is \it completely reconstructed from the low energy CP-phases measured by neutrino oscillation and neutrinoless double-beta decay experiments. We reveal and analyze two distinct classes of such minimal schemes that are shown to be highly predictive. Extension of our reconstruction formalism to a three-heavy-neutrino seesaw is discussed.
- We study the unitarity of the standard model (SM) in higher dimensions. We show that the essential features of SM unitarity remain after compactification, and place bounds on the highest Kaluza-Klein (KK) level N_KK and the Higgs mass m_H in the effective four-dimensional (4d) low-energy theory. We demonstrate these general observations by explicitly analyzing the effective 4d KK theory of a compactified 5d SM on S^1/Z_2. The nontrivial energy cancellations in the scattering of longitudinal KK gluons or KK weak bosons, a consequence of the geometric Higgs mechanism, are verified. In the case of the electroweak gauge bosons, the longitudinal KK states also include a small mixture from the KK Higgs excitations. With the analyses before and after compactification, we derive the strongest bounds on N_KK from gauge KK scattering. Applying these bounds to higher-dimensional SUSY GUTs implies that only a small number of KK states can be used to accelerate gauge coupling unification. As a consequence, we show that the GUT scale in the 5d minimal SUSY GUT cannot be lower than about 10^14 GeV.
- Interaction of Higgs scalar (H) with weak gauge bosons (V=W,Z) is the \it key to understand electroweak symmetry breaking (EWSB) mechanism. New physics effects in the HVV interactions, as predicted by models of compositeness, supersymmetry and extra dimensions, can be formulated as anomalous couplings via a generic effective Lagrangian. We first show that the existing electroweak precision data already impose nontrivial indirect constraints on the anomalous HVV couplings. Then, we systematically study VV --> VV scatterings in the TeV region, via Gold-plated pure leptonic decay modes of the weak bosons. We demonstrate that, even for a light Higgs boson in the mass range 115GeV < m_H < 300GeV, this process can directly probe the anomalous HVV interactions at the LHC with an integrated luminosity of 300fb^-1, which further supports the ``No-Lose'' theorem for the LHC to uncover the EWSB mechanism. Comparisons with the constraints from measuring the cross section of VH associate production and the Higgs boson decay width are also given.
- We study single charged Higgs boson production in photon-photon collision as a probe of the new dynamics of Higgs interactions. This is particularly important when the mass ($M_{H^\pm}$) of charged Higgs bosons ($H^{\pm}$) is relatively heavy and above the kinematic limit of the pair production ($M_{H^\pm} > \sqrt{s}/2$). We analyze the cross sections of single charged Higgs boson production from the photon-photon fusion processes, $\gamma\gamma\to \tau \bar \nu H^+$ and $\gamma\gamma\to b \bar c H^+$, as motivated by the minimal supersymmetric standard model and the dynamical Topcolor model. We find that the cross sections at such a $\gamma\gamma$ collider can be sufficiently large even for $M_{H^\pm} > \sqrt{s}/2$, and is typically one to two orders of magnitude higher than that at its parent $e^-e^+$ collider. We further demonstrate that the polarized photon beams can provide an important means to determine the chirality structure of Higgs Yukawa interactions with the fermions.
- Motivated by the recent strong experimental evidence of large \nu_mu-\nu_tau neutrino mixing, we explore current bounds on the analogous mixing in the charged lepton sector. We present a general formalism for dimension-6 fermionic effective operators involving tau-mu mixing with typical Lorentz structure (\barmu \Gamma tau)(\barq^a \Gamma q^b), and discuss their relationship to the standard model gauge symmetry and the underlying flavor dynamics. We derive the low-energy constraints on the new physics scale associated with each operator, mostly from current experimental bounds on rare decay processes of tau, hadrons or heavy quarks. For operators involving at least one light quark (u,d,s), these constraints typically give a bound on the new physics scale of a few TeV or higher. Those operators with two heavy quarks turn out to be more weakly constrained at the present, giving bounds of a few hundred GeV. A few scalar and pseudo-scalar operators are free from all current experimental constraints.
- Existing oscillation data point to nonzero neutrino masses with large mixings. We analyze the generic features of the neutrino Majorana mass matrix with inverted hierarchy and construct realistic \it minimal schemes for the neutrino mass matrix that can explain the large (but not maximal) \nu_e - \nu_mu mixing of MSW-LAM as well as the nearly maximal \nu_mu - \nu_tau mixing and the small (or negligible) \nu_e --> \nu_tau transition. These minimal schemes are quite unique and turn out to be extremely predictive. Implications for neutrinoless double beta decay, tritium beta decay and cosmology are analyzed.
- When the charged Higgs boson is too heavy to be produced in pairs, the predominant production mechanism at Linear Colliders is via the single charged Higgs boson production processes, such as $e^-e^+ \to b \bar c H^+, \tau \bar \nu H^+$ and $\gamma\gamma \to b \bar c H^+, \tau \bar \nu H^+$. We show that the yield of a heavy charged Higgs boson at a $\gamma\gamma$ collider is typically one or two orders of magnitude larger than that at an $e^-e^+$ collider. Furthermore, a polarized $\gamma\gamma$ collider can determine the chirality of the Yukawa couplings of fermions with charged Higgs boson via single charged Higgs boson production, and thus discriminate models of new physics.
- DAMA is searching for rare processes by developing and using several kinds of radiopure scintillators: in particular, NaI(Tl), liquid Xenon and CaF$_2$(Eu). The main results are here summarized with particular attention to the investigation of the WIMP annual modulation signature.
- We present a complete study of the vacuum structure of Top Quark Seesaw models of the Electroweak Symmetry Breaking, including bottom quark mass generation. Such models emerge naturally from extra dimensions. We perform a systematic gap equation analysis and develop an improved broken phase formulation for including exact seesaw mixings. The composite Higgs boson spectrum is studied in the large-N_c fermion-bubble approximation and an improved renormalization group approach. The theoretically allowed parameter space is restrictive, leading to well-defined predictions. We further analyze the electroweak precision constraints. Generically, a heavy composite Higgs boson with a mass of ~1TeV is predicted, yet fully compatible with the precision data.
- The squark mass-matrix from the soft supersymmetry (SUSY) breaking sector contains a rich flavor-mixing structure that allows O(1) mixings among top- and charm-squarks while being consistent with all the existing theoretical and experimental bounds. We formulate a \it minimal flavor-changing-neutral current scheme in which the squark mixings arise from the non-diagonal scalar trilinear interactions. This feature can be realized in a class of new models with horizontal U(1)_H symmetry which generates realistic quark-mass matrices and provides a solution to the SUSY \mu-problem. Finally, without using the mass-insertion approximation, we analyze SUSY radiative corrections to the bcH^+ and tch^0 couplings, and show that these couplings can reveal exciting new discovery channels for the Higgs boson signals at the Tevatron and the LHC.
- We study the discovery reach of the Tevatron and the LHC for detecting a Higgs boson (h), predicted in composite models of the electroweak symmetry breaking or in supersymmetric theories, with an enhanced b-quark Yukawa coupling via p \barp / p p \to b \bbar h (\to b \bbar) + X. Our analysis shows that studying this process at the Tevatron Run II or the LHC can provide strong constraints on these models.