International Journal of Modern Physics A

We review the status and future of direct searches for light dark matter. We start by answering the question: "Whatever happened to the light dark matter anomalies?" i.e. the fate of the potential dark matter signals observed by the CoGeNT, CRESST-II, CDMS-Si and DAMA/LIBRA experiments. We discuss how the excess events in the first two of these experiments have been explained by previously underestimated backgrounds. For DAMA, we summarize the progress and future of mundane explanations for the annual modulation reported in its event rate. Concerning the future of direct detection, we focus on the irreducible background from solar neutrinos. We explain broadly how it will affect future searches and summarize efforts to mitigate its effects.

In a supersymmetric U(1)′ seesaw model, a right-handed sneutrino can be a good thermal dark matter candidate if the extra gaugino is light enough to provide an appropriate annihilation cross-section through a t-channel diagram. We first discuss how right thermal relic density of the right-handed sneutrino dark matter can arise and then explore lepton number and flavor violating signatures followed by cascade production of from the third generation squarks at the LHC.

We study spherically symmetric finite energy solutions of two Higgs–Chern–Simons-Yang–Mills–Higgs (HCS-YMH) models in 3+1 dimensions, one with gauge group SO(5) and the other with SU(3). The Chern–Simons (CS) densities are defined in terms of both the Yang–Mills (YM) and Higgs fields and the choice of the two gauge groups is made so that they do not vanish. The solutions of the SO(5) model carry only electric charge and zero magnetic charge, while the solutions of the SU(3) model are dyons carrying both electric and magnetic charges like the Julia–Zee (JZ) dyon. Unlike the latter, however, the electric charge in both models receives an important contribution from the CS dynamics. We pay special attention to the relation between the energies and charges of these solutions. In contrast with the electrically charged JZ dyon of the Yang–Mills–Higgs (YMH) system, whose mass is larger than that of the electrically neutral (magnetic monopole) solutions, the masses of the electrically charged solutions of our HCS-YMH models can be smaller than their electrically neutral counterparts in some parts of the parameter space. To establish this is the main task of this work, which is performed by constructing the HCS-YMH solutions numerically. In the case of the SU(3) HCS-YMH, we have considered the question of angular momentum and it turns out that it vanishes.

We discuss the interplay between standard canonical analysis and canonical discretization in three-dimensional gravity with cosmological constant. By using the Hamiltonian analysis, we find that the continuum local symmetries of the theory are given by the on-shell space–time diffeomorphisms, which at the action level, correspond to the Kalb–Ramond transformations. At the time of discretization, although this symmetry is explicitly broken, we prove that the theory still preserves certain gauge freedom generated by a constant curvature relation in terms of holonomies and the Gauss's law in the lattice approach.

The phenomenon of fermion production in a 5D FRW space–time with a warped extra dimension is studied by considering the canonical method based on Bogoliubov transformation connecting the "in" with the "out" states. For an exactly solvable model, two sets of exact solution are expressed in terms of Bessel functions. Studying the semiclassical Hamilton–Jacobi equation, the "in" and "out" states are identified. The pair creation probability and the mean number of created particles are calculated from the Bogoliubov coefficients. It is shown that the particle creation probability and the number density of created particles depend on the ratio of the scale factors associated with the ordinary space {x} and the extra dimension. It is also shown that the contraction of the extra dimension induces particle creation like the ordinary space expansion.

Perturbative QCD in mass independent schemes leads in general to running coupling a(Q²) which is nonanalytic (nonholomorphic) in the regime of low spacelike momenta |Q²|≲1 GeV². Such (Landau) singularities are inconvenient in the following sense: evaluations of spacelike physical quantities 𝒟(Q²) with such a running coupling a(κQ²)(κ~1) give us expressions with the same kind of singularities, while the general principles of local quantum field theory require that the mentioned physical quantities have no such singularities. In a previous work, certain classes of perturbative mass independent beta functions were found such that the resulting coupling was holomorphic. However, the resulting perturbation series showed explosive increase of coefficients already at N⁴LO order, as a consequence of the requirement that the theory reproduce the correct value of the τ lepton semihadronic strangeless decay ratio r_τ. In this paper, we successfully extend the construction to specific classes of perturbative beta functions such that the perturbation series do not show explosive increase of coefficients, the perturbative coupling is holomorphic, and the correct value of r_τ is reproduced. In addition, we extract, with Borel sum rule analysis of the V+A channel of the semihadronic strangeless decays of τ lepton, reasonable values of the corresponding D = 4 and D = 6 condensates.

Vector particles' Hawking radiation as tunneling from the apparent horizon of Vaidya black holes is investigated. By applying the WKB approximation and the appropriate ansatz for the form of the action to the Proca equation, we obtain the tunneling spectrum of vector particles. As a result, the expected Hawking temperature is recovered by vector particles tunneling from the apparent horizon of Vaidya black holes.

In this paper, it is proven that the associative octons including scalar, pseudoscalar, pseudovector and vector values are convenient and capable tools to generalize the Maxwell–Dirac like field equations of electromagnetism and linear gravity in a compact and simple way. Although an attempt to describe the massless field equations of electromagnetism and linear gravity needs the sixteen real component mathematical structures, it is proved that these equations can be formulated in terms of eight components of octons. Furthermore, the generalized wave equation in terms of potentials is derived in the presence of electromagnetic and gravitational charges (masses). Finally, conservation of energy concept has also been investigated for massless fields.

We discuss a sufficiently large four-dimensional Schwarzschild black hole which is in equilibrium with a heat bath. In other words, we consider a black hole which has grown up from a small one in the heat bath adiabatically. We express the metric of the interior of the black hole in terms of two functions: One is the intensity of the Hawking radiation, and the other is the ratio between the radiation energy and the pressure in the radial direction. Especially in the case of conformal matters we check that it is a self-consistent solution of the semiclassical Einstein equation, G_μν = 8πG〈T_μν〉. It is shown that the strength of the Hawking radiation is proportional to the c-coefficient, that is, the coefficient of the square of the Weyl tensor in the four-dimensional Weyl anomaly.

The realization of a nonlocal quantum field theory without losing unitarity, gauge invariance and causality is investigated. It is commonly retained that such a formulation is possible at tree level, but at quantum level acausality is expected to reappear at one loop. We suggest that the problem of acausality is, in a broad sense, similar to the one about anomalies in quantum field theory. By virtue of this analogy, we suggest that acausal diagrams resulting from the fermionic sector and the bosonic one might cancel each other, with a suitable content of fields and suitable symmetries. As a simple example, we show how supersymmetry can alleviate this problem in a simple and elegant way, i.e. by leading to exact cancellations of harmful diagrams, to all orders of perturbation theory. An infinite number of divergent diagrams cancel each other by virtue of the nonrenormalization theorem of supersymmetry. However, supersymmetry is not enough to protect a theory from all acausal divergences. For instance, acausal contributions to supersymmetric corrections to D-terms are not protected by supersymmetry. On the other hand, we show in detail how supersymmetry also helps in dealing with D-terms: divergences are not canceled but they become softer than in the nonsupersymmetric case. The supergraphs' formalism turns out to be a powerful tool to reduce the complexity of perturbative calculations.