119119504
Constraints on Light Majorana dark Matter from Colliders
Abstract We explore model-independent collider constraints on light Majorana dark matter particles. We find that colliders provide a complementary probe of WIMPs to direct detection, and give the strongest current constraints on light DM particles. Collider experiments can access interactions not probed by direct detection searches, and outperform direct detection experiments by about an order of magnitude for certain operators in a large part of parameter space. For operators which are suppressed at low momentum transfer, collider searches have already placed constraints on such operators limiting their use as an explanation for DAMA.
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.
119123919
Fermion Mass Hierarchy and Proton Stability from Non-anomalous U(1)(F) in SUSY SU(5)
We present a realistic supersymmetric SU(5) model combined with a nonanomalous U(1){sub F} symmetry. We find a set of U(1){sub F} charges which automatically lead to the realistic mass hierarchy and mixing patterns for quarks, leptons, and neutrinos. All gauge anomalies, including the [U(1){sub F}]{sup 3} anomaly, are canceled in our model without invoking the Green-Schwarz mechanism or having exotic fields. Proton decay mediated by dimension-5 operators is automatically suppressed in our model, because the scale set by the largest right-handed neutrino mass is much less than the GUT scale.
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.
119114689
Gamma ray line constraints on effective theories of dark matter
Abstract A monochromatic gamma ray line results when dark matter particles in the galactic halo annihilate to produce a two body final state which includes a photon. Such a signal is very distinctive from astrophysical backgrounds, and thus represents an incisive probe of theories of dark matter. We compare the recent null results of searches for gamma ray lines in the galactic center and other regions of the sky with the predictions of effective theories describing the interactions of dark matter particles with the Standard Model. We find that the null results of these searches provide constraints on the nature of dark matter interactions with ordinary matter which are complementary to constraints from other observables, and stronger than collider constraints in some cases.
118099142
Ruling Out the Light Higgs Boson by Kaon Decay
We re-examine the theoretical estimates of the decay K → πH and the experimental constraints on the existence of a light Higgs boson from this process. We find that: (i) pole diagrams generated from the Higgs-gluon coupling via a loop of heavy quarks do contribute to K → πH, (ii) there is an additional contribution to the K → πH amplitude coming from the effective KHW and πHW couplings, (iii) even if B, the unknown parameter in the chiral-Lagrangian description of K → πH transitions, is nonzero and even if the real part of the K → πH amplitude is canceled accidentally, the imaginary contribution alone suffices to rule out a Higgs boson lighter than 2m π, and (iv) whether Higgs bosons in the mass range 2m π < m H < 350 MeV are excluded by the imaginary part of the K → πH amplitude depends on the branching ratio of H → µ + µ -,a+p, — and the top-quark mass. Decay modes K L → π+π- H and K + → l+ vH are briefly discussed.
115976565
Heavy Quark and Chiral Symmetry in Heavy Baryons
120346822
NOETHER CHARGES, BLACK HOLES AND THE IMMIRZI PARAMETER
We have shown that terms in the action which won't contribute to local equation of motions do contribute to globally conversed physical quantities in classical theories of gravity due to general coordinate covariance. This observation allows one to determining the Immirzi parameter in the Ashtekar variable formulation of gravitational theories even at classical level. Applying Wald's Noether charge approach and identifying the entropy on black hole horizon as the Noether charge for translation, one can demonstrate explicitly that the Immirzi parameter does make its contributions through the boundary term. Our results also shed lights in connecting the Immirzi paramter to quasi-normal modes of black holes.
14974262
Quantum states with negative energy density in the Dirac field and quantum inequalities
Abstract Energy densities of the quantum states that are superposition of two multi-electron–positron states are examined. It is shown that the energy densities can be negative when two multi-particle states have the same number of electrons and positrons or when one state has one more electron–positron pair than the other. In the cases in which negative energy could arise, we find that the energy is that of a positive constant plus a propagating part which oscillates between positive and negative, and the energy can dip to negative at some places for a certain period of time if the quantum states are properly manipulated. It is demonstrated that the negative energy densities satisfy the quantum inequality. Our results also reveal that for a given particle content, the detection of negative energy is an operation that depends on the frame where any measurement is to be performed. This suggests that the sign of energy density for a quantum state may be a coordinate-dependent quantity in quantum theory.
119780320
OBSERVABLE CONSEQUENCES OF THE STRONG COUPLING PHASE OF QED HYPOTHESIZED NEAR THE SURFACE OF LARGE-Z NUCLEI
We discuss observable effects of the assumption that the strong coupling phase of quantum electrodynamics is realized in the surface region of heavy nuclei with large atomic number Z under a suitable external disturbance. We present some comments on anomalous peaks in electron-positron systems observed in heavy ion reactions and on effects expected in electron and positron scatterings off large-Z nuclei. We propose some experiments to test our assumption: (1) coincidence measurement of e+e− and γγ signals from the decays of large-Z nuclei, and (2) spectroscopy of large-Z muonic atoms.