International Journal of Modern Physics A

Various aspects of the high-energy emission from relativistic jets associated with compact astrophysical systems are reviewed. The main leptonic and hadronic processes responsible for the production of high-energy γ-rays, very-high-energy neutrinos and ultra-high energy cosmic rays are discussed. Relations between the γγ pair production and photomeson production opacities are derived, and their consequences for the relative emission of γ-rays and neutrinos are examined. The scaling of the size and location of the various emission zones and other quantities with black hole mass and dimensionless luminosity is elucidated. The results are applied to individual classes of objects, including blazars, microquasars and gamma-ray bursts. It is concluded that if baryons are present in the jet at sufficient quantities, then under optimal conditions most systems exhibiting relativistic jets may be detectable by upcoming neutrino telescopes. An exception is the class of TeV blazars, for which γ-ray observations imply neutrino yields well below detection limit.

We study the time-dependent dynamics of a collection of N collapsing/expanding D0-branes in type IIA string theory. We show that the fuzzy-S³ and S⁵ provide time-dependent solutions to the matrix model of D0-branes and its DBI generalisation. Some intriguing cancellations in the calculation of the non-Abelian DBI matrix actions result in the fuzzy-S³ and S⁵ having the same dynamics at large-N. For the matrix model, we find analytic solutions describing the time-dependent radius, in terms of Jacobi elliptic functions. Investigation of the physical properties of these configurations shows that there are no bounces for the trajectory of the collapse at large-N. We also write down a set of useful identities for fuzzy-S³, fuzzy-S⁵ and general fuzzy odd-spheres.

We obtain a generalized Schwarzschild (GS) and a generalized Reissner–Nordstrom (GRN) black hole geometries in 3+1 dimensions, in a noncommutative string theory. In particular, we consider an effective theory of gravity on a curved D₃-brane in presence of an electromagnetic (EM) field. Two different length scales, inherent in its noncommutative counterpart, are exploited to obtain a theory of effective gravity coupled to an U(1) noncommutative gauge theory to all orders in Θ. It is shown that the GRN-black hole geometry, in the Planckian regime, reduces to the GS-black hole. However in the classical regime it may be seen to govern both the Reissner–Nordstrom and the Schwarzschild geometries. The emerging notion of 2D black holes evident in the framework are analyzed. It is argued that the D-string in the theory may be described by the near horizon 2D black hole geometry, in the gravity decoupling limit. Finally, our analysis explains the nature of the effective force derived from the nonlinear EM-field and accounts for the Hawking radiation phenomenon in the formalism.

We study the consequences of the generalized Heisenberg uncertainty relation which admits a minimal uncertainty in length such as the case in a theory of quantum gravity. In particular, the theory of quantum harmonic oscillators arising from such a generalized uncertainty relation is examined. We demonstrate that all the standard properties of the quantum harmonic oscillators prevail when we employ a generalized momentum. We also show that quantum electrodynamics and coherent photon states can be described in the familiar standard manner despite the generalized uncertainty principle.

A systematic calculation for the transition form factors of heavy to light mesons (B, B_s, D, D_s → π, K, η, ρ, K*, ω, ϕ) is carried out by using light-cone sum rules in the framework of heavy quark effective field theory. The heavy quark symmetry at the leading order of 1/m_Q expansion enables us to reduce the independent wave functions and establish interesting relations among form factors. Some relations hold for the whole region of momentum transfer. The meson distribution amplitudes up to twist-4 including the contributions from higher conformal spin partial waves and light meson mass corrections are considered. The CKM matrix elements |V_ub|, |V_cs| and |V_cd| are extracted from some relatively well-measured decay channels. A detailed prediction for the branching ratios of heavy to light meson decays is then presented. The resulting predictions for the semileptonic and radiative decay rates of heavy to light mesons (B, B_s, D, D_s → π, K, η, ρ, K*, ω, ϕ) are found to be compatible with the current experimental data and can be tested by more precise experiments at B-factory, LHCb, BEPCII and CLEOc.

We investigate the Dynamical Casimir Effect (DCE) in the case of a scalar field enclosed in a box which undergoes a phase of strong acceleration (a kick) during its motion. Following a general-relativistic approach, we describe the acceleration field as a time-dependent space–time metric in the frame of a comoving, noninertial observer. Assuming a nonrelativistic motion of the box, we perturbatively solve the Klein–Gordon equation for the matter field, evaluating the β-Bogolubov coefficients, related to the particle creation. We show that, after the kick, a (small) number of created quanta is found inside the box. The resulting spectrum carries, in principle, information about the details of the box acceleration phase. The present approach can serve to shed light on the close relationship between DCE and Unruh–Hawking effect.

In this paper we compute the correction to the entropy of Schwarzschild black hole due to the vacuum polarization effect of massive scalar field. The Schwarzschild black hole is supposed to be confined in spherical shell. The scalar field obeying mixed boundary condition on the spherical shell.

We study a U(N) gauged supergravity model with one hypermultiplet parametrizing SO(4, 1)/SO(4) quaternionic manifold. Local supersymmetry is known to be spontaneously broken to in the Higgs phase of U(1)_graviphoton × U(1). Several properties are obtained of this model in the vacuum of unbroken SU(N) gauge group. In particular, we derive mass spectrum analogous to the rigid counterpart and put the entire resulting potential on this vacuum in the standard superpotential form of supergravity.

The influence of Lorentz- and CPT-violating terms (in "vector" and "axial vector" couplings) on the Dirac equation is explicitly analyzed: plane-wave solutions, dispersion relations and eigenenergies are explicitly obtained. The nonrelativistic limit is worked out and the Lorentz-violating Hamiltonian identified in both cases, in full agreement with the results already established in the literature. Finally, the physical implications of this Hamiltonian on the spectrum of hydrogen are evaluated both in the absence and presence of a magnetic external field. It is observed that the fixed background, when considered in a vector coupling, yields no qualitative modification in the hydrogen spectrum, whereas it does provide an effective Zeeman-like splitting of the spectral lines whenever coupled in the axial vector form. It is also argued that the presence of an external fixed field does not imply new modifications on the spectrum.

In the present study on proton–Beryllium collisions at two distinctly different energies obtained by one FERMILAB Collaboration, we attempt to focus on the unsettled controversy between the exponential models versus power law models, both of which are found to be in wide applications. The study concludes that none of them could be abandoned finally. And the resolution of the debate, the authors argue, might rest, not on the acceptance of just any one of them, but on a suitable combination of both of them, acting in the different domains of the transverse momentum values.