119198751
Minimal flavor violation in the lepton sector of the Randall–Sundrum model
Abstract We propose a realization of Minimal Flavor Violation in the lepton sector of the Randall–Sundrum model. With the MFV assumption, the only source of flavor violation are the 5 D Yukawa couplings, and the usual two independent sources of flavor violation are related. In the limit of massless neutrinos, the bulk mass matrices and 5 D Yukawa matrices are simultaneously diagonalized, and hence the absence of FCNCs. In the case of massive neutrinos, the contributions to FCNCs in the charged lepton sector are highly suppressed, due to the smallness of neutrino masses. In addition, the MFV assumption also allows suppressing one-loop charged current contributions to flavor changing processes by reducing the size of the Yukawa couplings, which is not possible in the generic anarchical case. We found that the first KK mass scale as low as ∼ 3 TeV can be allowed. In both cases, we present a set of numerical results that give rise to realistic lepton masses and mixing angles. Mild hierarchy in the 5 D Yukawa matrix of O ( 25 ) in our numerical example is required to be consistent with two large and one small mixing angles. This tuning could be improved by having a more thorough search of the parameter space.
67849491
Constraints on Dark Matter from Colliders
We show that colliders can impose strong constraints on models of dark matter, in particular, when the dark matter is light. We analyze models where the dark matter is a fermion or scalar interacting with quarks and/or gluons through an effective theory containing higher dimensional operators which represent heavier states that have been integrated out of the effective field theory. We determine bounds from existing Tevatron searches for monojets as well as expected LHC reaches for a discovery. We find that colliders can provide information which is complementary or in some cases even superior to experiments searching for direct detection of dark matter through its scattering with nuclei. In particular, both the Tevatron and the LHC can outperform spin-dependent searches by an order of magnitude or better over much of the parameter space, and if the dark matter couples mainly to gluons, the LHC can place bounds superior to any spin-independent search.
118458603
Thermal relics in hidden sectors
Dark matter may be hidden, with no standard model gauge interactions. At the same time, in WIMPless models (WIMP: weakly interacting massive particles) with hidden matter masses proportional to hidden gauge couplings squared, the hidden dark matter's thermal relic density may naturally be in the right range, preserving the key quantitative virtue of WIMPs. We consider this possibility in detail. We first determine model-independent constraints on hidden sectors from big bang nucleosynthesis and the cosmic microwave background. Contrary to conventional wisdom, large hidden sectors are easily accommodated. A flavour-free version of the standard model is allowed if the hidden sector is just 30% colder than the observable sector after reheating. Alternatively, if the hidden sector contains a one-generation version of the standard model with characteristic mass scale below 1 MeV, even identical reheating temperatures are allowed. We then analyse hidden sector freeze-out in detail for a concrete model, solving the Boltzmann equation numerically and explaining the results from both observable and hidden sector points of view. We find that WIMPless dark matter does indeed obtain the correct relic density for masses in the range . The upper bound results from the requirement of perturbativity, and the lower bound assumes that the observable and hidden sectors reheat to the same temperature, and is raised to the MeV scale if the hidden sector is ten times colder. WIMPless dark matter therefore generalizes the WIMP paradigm to the largest mass range possible for viable thermal relics and provides a unified framework for exploring dark matter signals across nine orders of magnitude in dark matter mass.
119204000
Hidden charged dark matter
Can dark matter be stabilized by charge conservation, just as the electron is in the standard model? We examine the possibility that dark matter is hidden, that is, neutral under all standard model gauge interactions, but charged under an exact {\rm U}(1) gauge symmetry of the hidden sector. Such candidates are predicted in WIMPless models, supersymmetric models in which hidden dark matter has the desired thermal relic density for a wide range of masses. Hidden charged dark matter has many novel properties not shared by neutral dark matter: (1) bound state formation and Sommerfeld-enhanced annihilation after chemical freeze out may reduce its relic density, (2) similar effects greatly enhance dark matter annihilation in protohalos at redshifts of z ~ 30, (3) Compton scattering off hidden photons delays kinetic decoupling, suppressing small scale structure, and (4) Rutherford scattering makes such dark matter self-interacting and collisional, potentially impacting properties of the Bullet Cluster and the observed morphology of galactic halos. We analyze all of these effects in a WIMPless model in which the hidden sector is a simplified version of the minimal supersymmetric standard model and the dark matter is a hidden sector stau. We find that charged hidden dark matter is viable and consistent with the correct relic density for reasonable model parameters and dark matter masses in the range 1 GeV  mX  10 TeV. At the same time, in the preferred range of parameters, this model predicts cores in the dark matter halos of small galaxies and other halo properties that may be within the reach of future observations. These models therefore provide a viable and well-motivated framework for collisional dark matter with Sommerfeld enhancement, with novel implications for astrophysics and dark matter searches.
16773975
The Correction Of Scattering Cross Section Led By Noncommutative Effects
Möller Scattering and Bhabha Scattering on noncommutative spacetime is restudied. A new result is reported. It is shown that the correction of scattering cross sections led by the noncommutative effects is not always enhancement with the total energy of colliding electrons, but there is an optimal collision energy to get the greatest noncommutative correction for noncommutative effect. Moreover there is a linear relation between the noncommutative threshold energy and optimal collision energy, so that the noncommutative threshold energy can be deterimed by experiment in the next generation collider.
119367982
An SO(10) GUT Model with $S4$ Flavor Symmetry
We present a supersymmetric grand unification model based on SO(10) group with $S4$ flavor symmetry. In this model, the fermion masses are from Yukawa couplings involving $\bf{10}$ and $\bar{\bf{126}}$ Higgs multiplets and the flavor structures of mass matrices of both quarks and leptons are determined by spontaneously broken $S4$. This model fits all of the masses and mixing angles of the quarks and leptons. For the most general CP-violation scenario, this model gives $\sin\theta_{13}$ a wide range of values from zero to the current bound with the most probable values $0.02-0.09$. With certain assumptions where leptonic phases have same CP-violation source as CKM phase, one gets a narrower range $0.03-0.09$ for $\sin\theta_{13}$ with the most probable values $0.04-0.08$. This model gives leptonic Dirac CP phase the most probable values 2-4 radians in the general CP-violation case.
125027666
Restudies of Searching for 1~(-+) Exotic State
In order to convenience for the data analysis of BES some new relations which can be used to search for the 1~(-+) exotic state in J/φ→ωX, X→KKπ have been obtained. How to search for the 1~(-+) exotic state in the three--step two--body hadronic decay process J/φ→ωX, X→KK~*, K~*→Kπ is also discussed.
17177636
Quantum Gravity and Astrophysics: The Microwave Background and Other Thermal Sources
The problem of formulating a fully consistent quantum gravity theory (QGT) has not yet been solved. Even before we are able to work out the details of a complete theory, however, we do know some important qualitative features to be expected in any quantum theory. Fluctuations of the metric, for example, are expected and are associated with fluctuations of the lightcone. Lightcone fluctuations affect the arrival time of signals from distant sources in potentially measurable ways, broadening the spectra. In this paper, we start with a thermal spectrum and derive the form of spectral changes expected in a wide class of QGTs. We apply these results, valid for any thermal spectrum, to the cosmic microwave background (CMB). The CMB offers two advantages: (1) deviations from a thermal spectrum are well constrained, and (2) the radiation emanates from the most distant source of light, the surface of last scattering. We use existing CMB data to derive an upper bound on the value of $\Delta t,$ the mean spread in arrival times due to metric fluctuations: ${\Delta t} < 2.1 \times 10^{-14}$ s at the 95% confidence limit. This limit applies to a wide range of QGTs, and falsifies those predicting a larger spread in arrival times. We find this limit rules out at least one QGT, the 5-dimensional theory in which the "extra" dimension is flat. Tests of other models may also be possible, depending on the results of calculations to predict values of \Delta t,$ and also a second time scale, $\tau_c,$ the correlation time, which is the characteristic time scale of the metric fluctuations. We show that stronger limits on the value of $\Delta t,$ hence on lightcone fluctuations, can likely be derived through observations of of higher-T sources, e.g., in the X-ray and gamma-ray regimes.
120524340
PQCD analysis of exclusive charmless B meson decay spectra
Abstract We apply the perturbative QCD formalism, including Sudakov effects, to exclusive charmless semi-leptonic B meson decays. Predictions for both the charged lepton and lepton pair invariant mass spectra of the B → π l ν and B → ϱ l ν decays in the large recoil region are presented. After combining soft pionn results, we extract | V ub | ≤ 4.5 × 10 −3 from curren data. With our predictions, future data will not only provide a more precise extraction of | V ub |, but also test perturbative QCD in B meson decays.
119699165
STUDY ON HADRONIC DECAY OF THE LOWEST LYING GLUEBALLS WITH JPC=even++ TO TWO PSEUDOSCALAR MESONS
Taking into account the possible glueball component in the final state mesons, we investigate the hadronic decay modes of the lowest lying glueballs (G) with JPC=even++ to two pseudoscalar mesons (PP). The naive estimations of $\frac{\tilde\Gamma(G\rightarrow PP)}{\tilde\Gamma(G\rightarrow K\bar K)}$ for scalar and tensor glueballs are given.
18104286
MODIFICATION OF KAWAI MODEL ABOUT THE MIXING OF THE PSEUDOSCALAR MESONS
The Kawai model describing the glueball–quarkonia mixing is modified. The mixing of η, η′ and η(1410) is re-investigated based on the modified Kawai model. The glueball–quarkonia content of the three states is determined from a fit to the data of the electromagnetic decays involving η, η′. Some predictions about the electromagnetic decays involving η(1410) are presented.