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.
119090796
Fulling–Davies–Unruh effect and spontaneous excitation of an accelerated atom interacting with a quantum scalar field
Abstract We investigate, from the point of view of a coaccelerated frame, the spontaneous excitation of a uniformly accelerated two-level atom interacting with a scalar field in a thermal state at a finite temperature T and show that the same spontaneous excitation rate for the uniformly accelerated atom in the Minkowski vacuum obtained in the inertial frame can only be recovered in the coaccelerated frame assuming a thermal bath at the Fulling–Davies–Unruh temperature T FDU = a / 2 π for what appears to be the Minkowski vacuum to the inertial observer. Our discussion provides another example of a physical process different from those examined before in the literature to better understand the Fulling–Davies–Unruh effect.
119124346
Unruh effect and entanglement generation for accelerated atoms near a reflecting boundary
We study, in the framework of open systems, the entanglement generation of two independent uniformly accelerated atoms in interaction with the vacuum fluctuations of massless scalar fields subjected to a reflecting plane boundary. We demonstrate that, with the presence of the boundary, the accelerated atoms exhibit distinct features from static ones in a thermal bath at the corresponding Unruh temperature in terms of the entanglement creation at the neighborhood of the initial time. In this sense, accelerated atoms in vacuum do not necessarily have to behave as if they were static in a thermal bath at the Unruh temperature.
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.
120986058
Quantum thermal aspects of uniformly accelerating charged black holes
115459673
LIGHTCONE FLUCTUATIONS AND EXTRA DIMENSIONS
124014107
Extraction of V(ub) from decay B ---> pi lepton neutrino
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
10829609
Halo-shape and relic-density exclusions of Sommerfeld-enhanced dark matter explanations of cosmic ray excesses.
Dark matter with Sommerfeld-enhanced annihilation has been proposed to explain observed cosmic ray positron excesses in the 10 GeV to TeV energy range. We show that the required enhancement implies thermal relic densities that are too small to be all of dark matter. We also show that the dark matter is sufficiently self-interacting that observations of elliptical galactic dark matter halos exclude large Sommerfeld enhancement for light force carriers. Resonant Sommerfeld enhancement does not modify these conclusions, and the astrophysical boosts required to resolve these discrepancies are disfavored, especially when significant self-interactions suppress halo substructure.
121463466
Critical exponents of new universality classes
Abstract We calculate critical exponents of chiral Ising, XY and Heisenberg universality classes up to second order in 4 − ϵ expansion. General expressions for any number N of fermionic variables are given and compared with recent extensive 1/ N calculation and lattice simulations. The possibility that these new universality classes describe critical phenomena in certain 3D magnetic systems and in finite temperature phase transitions of 3 + 1 dimensional quantum field theories is briefly discussed.
43002203
Black holes and Rindler superspace: Classical singularity and quantum unitarity
Canonical quantization of spherically symmetric initial data appropriate to classical interior black hole solutions in four dimensions is solved exactly without gauge fixing the remaining kinematic Gauss law constraint. The resultant mini-superspace manifold is two dimensional, of signature (+, -), nonsingular, and can be identified with the first Rindler wedge. The associated Wheeler-DeWitt equation with evolution in intrinsic superspace time is a free massive Klein-Gordon equation, and the Hamilton-Jacobi semiclassical limit of plane wave solutions can be matched to the interiors of Schwarzschild black holes. Classical black hole horizons and singularities correspond to the boundaries of the Rindler wedge. Exact wave functions of the Dirac equation in superspace are also considered. Precise correspondence between Schwarzschild black holes and free-particle mechanics in superspace is noted. Despite the presence of classical singularities, Hermiticity of the Dirac Hamiltonian operator, and thus unitarity of the quantum theory, is equivalent to an appropriate boundary condition which must be satisfied by the quantum states. This boundary condition holds for quite generic quantum wave packets of energy eigenstates, but fails for the usual Rindler fermion modes which are eigenstates with zero uncertainty in energy.