International Journal of Modern Physics A

Clusters of galaxies and the large scale filaments that connect neighboring clusters are expected to be sites of acceleration of charged particles and sources of non-thermal radiation from radio frequencies to gamma rays. Gamma rays are particularly interesting targets of investigation, since they may provide precious information on the nature and efficiency of the processes of acceleration and magnetic confinement of hadrons within clusters of galaxies. Here we review the status of viable scenarios that lead to the production of gamma rays from large scale structures and are compatible with the multifrequency observations that are already available. We also discuss the possibility of detection of gamma rays with space-borne telescopes such as GLAST and ground based Cherenkov telescopes, and the physical information that may be gathered from such observations.

Yang's theorem states that an initial J = 1 state cannot decay into two photons. Because of this result some reactions relating to elementary particles or atomic transitions can be ruled out. The theorem is not valid in the presence of background electric or magnetic fields. In this work we show that the decay of a J = 1 particle into two photons is permitted by the Bose symmetry and rotational invariance when the background of the decay process is not pure vacuum but contains an external classical magnetic/electric field. We also discuss constraints on these amplitudes from the CP invariance.

Color superconducting state has been known as a possible phase of quark matter with sufficiently large baryon number density so as for perturbative analysis to be valid. We point out that a color ferromagnetic state is another possible phase of such a sufficiently dense quark matter. Furthermore, we show under reasonable choices of parameters that the color ferromagnetic phase is energetically more favored than the color superconducting phase in the quark matter with smaller baryon number density. Supposing that increasing baryon density in neutron stars transforms nuclear matter into the quark matter of the color ferromagnetic phase, not color superconducting phase, we find that a critical mass of the neutron star with such an internal structure is about 1.6M_⊙.

The connection between the supersymmetric quantum mechanics involving two-component eigenfunctions and the stability equation associated with two classical configurations is investigated and a matrix superpotential is deduced. The question of stability is ensured for the Bogomol'nyi–Prasad–Sommerfield (BPS) states on two domain walls in a scalar potential model containing up to fourth-order powers in the fields, which is explicit demonstrated using the intertwining operators in terms of two-by-two matrix superpotential in the algebraic framework of supersymmetry in quantum mechanics. Also, a non-BPS state is found to be nonstable via the fluctuation Hessian matrix.

In this note we demonstrate that the algebra associated with coordinate transformations might contain the origins of a scalar field that can behave as an inflaton and/or a source for dark energy. We will call this particular scalar field the diffeomorphism scalar field. In one dimension, the algebra of coordinate transformations is the Virasoro algebra while the algebra of gauge transformations is the Kac–Moody algebra. An interesting representation of these algebras corresponds to certain field theories that have meaning in any dimension. In particular, the so-called Kac–Moody sector corresponds to Yang–Mills theories and the Virasoro sector corresponds to the diffeomorphism field theory that contains the scalar field and a rank-two symmetric, traceless tensor. We will focus on the contributions of the diffeomorphism scalar field to cosmology. We show that this scalar field can, qualitatively, act as a phantom dark energy, an inflaton, a dark matter source, and the cosmological constant Λ.

Parikh–Wilczek's recent work, which treats the Hawking radiation as semiclassical tunneling process from the event horizon of the static Schwarzschild and Reissner–Nordström black holes, indicates that the factually radiant spectrum deviates from the precisely thermal spectrum after taking the self-gravitation interaction into account. In this paper, we extend Parikh–Wilczek's work to study the Hawking radiation via tunneling from new form of rotating Kerr–Newman–Kasuya solution and obtain a corrected radiation spectrum, which is related to the change of Bekenstein–Hawking entropy, and is not pure thermal, but is consistent with the underlying unitary theory and then satisfies the first law of the black hole thermodynamics. Meanwhile, in this framework, we point out that the information conservation is only suitable for the reversible process.

Gauge-invariant systems in unconstrained configuration and phase spaces, equivalent to second-class constraints systems upon a gauge-fixing, are discussed. A mathematical pendulum on an (n-1)-dimensional sphere S^n-1 as an example of a mechanical second-class constraints system and the O(n) nonlinear sigma model as an example of a field theory under second-class constraints are discussed in details and quantized using the existence of underlying dilatation gauge symmetry and by solving the constraint equations explicitly. The underlying gauge symmetries involve, in general, velocity dependent gauge transformations and new auxiliary variables in extended configuration space. Systems under second-class holonomic constraints have gauge-invariant counterparts within original configuration and phase spaces. The Dirac's supplementary conditions for wave functions of first-class constraints systems are formulated in terms of the Wigner functions which admit, as we show, a broad set of physically equivalent supplementary conditions. Their concrete form depends on the manner the Wigner functions are extrapolated from the constraint submanifolds into the whole phase space.

The role of torsion and a scalar field ϕ in gravitation, especially, in the presence of a Dirac field in the background of a particular class of the Riemann–Cartan geometry is considered here. Recently, a Lagrangian density with Lagrange multipliers has been proposed by the author which has been obtained by picking some particular terms from the SO(4, 1) Pontryagin density, where the scalar field ϕ causes the de Sitter connection to have the proper dimension of a gauge field. In this paper the scalar field has been linked to the dimension of the Dirac field. Here we get the field equations for the Dirac field and the scalar field in such a way that both of them appear to be mutually noninteracting. In this scenario the scalar field appears to be a natural candidate for the dark matter and the dark radiation.

We consider some aspects of classical S-duality transformations in first-order actions taking into account the general covariance of the Dirac algorithm and the transformation properties of the Dirac bracket. By classical S-duality transformations we mean a field redefinition that interchanges the equations of motion and its associated Bianchi identities. By working from a first-order variational principle and performing the corresponding Dirac analysis we find that the standard electromagnetic duality can be reformulated as a canonical local transformation. The reduction from this phase space to the original phase space variables coincides with the well-known result about duality as a canonical nonlocal transformation. We have also applied our ideas to the bosonic string. These dualities are not canonical transformations for the Dirac bracket and relate actions with different kinetic terms in the reduced space.