119247899
Distinguishing dark matter annihilation enhancement scenarios via halo shapes
Abstract Sommerfeld enhancement and Breit–Wigner enhancement of the dark matter annihilation have been proposed to explain the “boost factor” which is suggested by observed cosmic ray excesses. Although these two scenarios can provide almost indistinguishable effects on the cosmic ray fluxes, the cross sections of the self-interaction in those enhancement mechanisms are drastically different. As a result, we might be able to distinguish them by examining the effects of the self-interaction on the dark matter halo shapes. In the Sommerfeld enhancement models with m ϕ ≲ 100 MeV and m DM ≲ 3 TeV , the self-interaction of dark matter can lead to more spherical dark halo. In the Breit–Wigner models, the dark matter is effectively collisionless.
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.
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.
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.
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.
7338034
Light-cone fluctuations in flat spacetimes with nontrivial topology
The quantum light-cone fluctuations in flat spacetimes with compactified spatial dimensions or with boundaries are examined. The discussion is based upon a model in which the source of the underlying metric fluctuations is taken to be quantized linear perturbations of the gravitational field. General expressions are derived, in the transverse trace-free gauge, for the summation of graviton polarization tensors, and for vacuum graviton two-point functions. Because of the fluctuating light cone, the flight time of photons between a source and a detector may be either longer or shorter than the light propagation time in the background classical spacetime. We calculate the mean deviations from the classical propagation time of photons due to the changes in the topology of the flat spacetime. These deviations are in general larger in the directions in which topology changes occur and are typically of the order of the Planck time, but they can get larger as the travel distance increases.
119351843
Spontaneous absorption of an accelerated hydrogen atom near a conducting plane in vacuum
We study, in the multipolar coupling scheme, a uniformly accelerated multilevel hydrogen atom in interaction with the quantum electromagnetic field near a conducting boundary and separately calculate the contributions of the vacuum fluctuation and radiation reaction to the rate of change of the mean atomic energy. It is found that the perfect balance between the contributions of vacuum fluctuations and radiation reaction that ensures the stability of ground-state atoms is disturbed, making spontaneous transition of ground-state atoms to excited states possible in a vacuum with a conducting boundary. The boundary-induced contribution is effectively a nonthermal correction, which enhances or weakens the nonthermal effect already present in the unbounded case, thus possibly making the effect easier to observe. An interesting feature worth noting is that the nonthermal corrections may vanish for atoms on some particular trajectories.
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.
118525095
Lamb shift for static atoms outside a Schwarzschild black hole
We study, by separately calculating the contributions of vacuum fluctuations and radiation reaction to the atomic energy level shift, the Lamb shift of a static two-level atom interacting with real massless scalar fields in the Boulware, Unruh, and Hartle-Hawking vacuums outside a Schwarzschild black hole. We find that in the Boulware vacuum, the Lamb shift gets a correction arising as a result of the backscattering of vacuum field modes off the space-time curvature, which is reminiscent of the correction to the Lamb shift induced by the presence of cavities. However, when the Unruh and Hartle-Hawking vacua are concerned, our results show that the Lamb shift behaves as if the atom were irradiated by a thermal radiation or immersed in a thermal bath at the Hawking temperature, depending on whether the scalar field is in the Unruh or the Hartle-Hawking vacuum. Remarkably, the thermal radiation is always backscattered by the space-time geometry.
16163396
Lightcone fluctuations in quantum gravity and extra dimensions
Abstract We discuss how compactified extra dimensions may have potentially observable effects which grow as the compactification scale decreases. This arises because of lightcone fluctuations in the uncompactified dimensions which can result in the broadening of the spectral lines from distant sources. We analyze this effect in a five dimensional model, and argue that data from gamma ray burst sources require the compactification length to be greater than about 105 cm in this model.