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.
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.
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.
59522874
Sommerfeld enhancements for thermal relic dark matter
The annihilation cross section of thermal relic dark matter determines both its relic density and indirect detection signals. We determine how large indirect signals may be in scenarios with Sommerfeld-enhanced annihilation, subject to the constraint that the dark matter has the correct relic density. This work refines our previous analysis through detailed treatments of resonant Sommerfeld enhancement and the effect of Sommerfeld enhancement on freeze out. Sommerfeld enhancements raise many interesting issues in the freeze out calculation, and we find that the cutoff of resonant enhancement, the equilibration of force carriers, the temperature of kinetic decoupling, and the efficiency of self-interactions for preserving thermal velocity distributions all play a role. These effects may have striking consequences; for example, for resonantly-enhanced Sommerfeld annihilation, dark matter freezes out but may then chemically recouple, implying highly suppressed indirect signals, in contrast to naive expectations. In the minimal scenario with standard astrophysical assumptions, and tuning all parameters to maximize the signal, we find that, for force-carrier mass m{sub {phi}=}250 MeV and dark matter masses m{sub X}=0.1, 0.3, and 1 TeV, the maximal Sommerfeld enhancement factors are S{sub eff}=7, 30, and 90, respectively. Such boosts are too small to explain both the PAMELA and Fermimore » excesses. Nonminimal models may require smaller boosts, but the bounds on S{sub eff} could also be more stringent, and dedicated freeze out analyses are required. For concreteness, we focus on 4{mu} final states, but we also discuss 4e and other modes, deviations from standard astrophysical assumptions and nonminimal particle physics models, and we outline the steps required to determine if such considerations may lead to a self-consistent explanation of the PAMELA or Fermi excesses.« less
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.
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.
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.
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.
16933705
ON THE MIXING OF THE SCALAR MESONS f0(1370), f0(1500) AND f0(1710)
Based on a 3 x 3 mass matrix describing the mixing of the scalar states f(o)(1370), f(o)(1500) and f(o)(1710), the hadronic decays of the three states into two pseudoscalar mesons are investigated. Under the possible assumption concerning the mass level order of the bare states \N] = \u (u) over bar + d (d) over bar]/root2, \S] = \s (s) over bar) and \G) = \gg] in the scalar sector, M-G > M-N > M-S, the implications of some of the observed branching ratios for the glueball-quarkonia content of the three states are studied. Some predictions about the decays of the three states are presented, which can provide stringent consistency checks for our assumption.
121894803
Hidden local symmetry and induced topological terms
Abstract Extending the previous derivation of an effective gauge theory from a generalized Nambu-Jona-Lasinio model, we show how the topological θ-term, θ Tr F F , can be generated dynamically in a similar fashion. These results provide a vivid demonstration of hidden local symmetry at work. Possible phenomenological implications of this approach are also discussed.