Mini-bangs in cosmology and astrophysics

The ideas originally proposed to discuss continuous creation of matter are reconsidered in the context of the big bang cosmological models. It is shown that singularity-free big bang models are possible under the modified field equations of general relativity. However, the case is made out that matter creation takes place in several mini-bangs at different epochs rather than in one big bang. The implications of this idea for high energy astrophysics and for gravitational radiation are discussed.     

Isometric embeddings in cosmology and astrophysics

Recent interest in higher-dimensional cosmological models has prompted some significant work on the mathematical technicalities of how one goes about embedding spacetimes into some higher-dimensional space. We survey results in the literature (existence theorems and simple explicit embeddings); briefly outline our work on global embeddings as well as explicit results for more complex geometries; and provide some examples. These results are contextualized physically, so as to provide a foundation for a detailed commentary on several key issues in the field such as: the meaning of ‘Ricci equivalent’ embeddings; the uniqueness of local (or global) embeddings; symmetry inheritance properties; and astrophysical constraints.     

Neutrino masses in astrophysics and cosmology

Cosmology yields the most restrictive limits on neutrino masses and conversely, massive neutrinos would contribute to the cosmic dark-matter density and would play an important role for the formation of structure in the universe. Neutrino oscillations may well solve the solar neutrino problem and can have a significant impact on supernova physics. The neutrino signal from a future galactic supernova could provide evidence for cosmologically interesting neutrino masses or set interesting limits.     

Constraining unparticle physics with cosmology and astrophysics

It has recently been suggested that a scale-invariant "unparticle" sector with a nontrivial infrared fixed point may couple to the standard model (SM) via higher-dimensional operators. The weakness of such interactions hides the unparticle phenomena at low energies. We demonstrate how cosmology and astrophysics can place significant bounds on the strength of unparticle-SM interactions. We also discuss the possibility of a having a non-negligible unparticle relic density today.     

Quark matter nucleation in hot hadronic matter

We study the quark deconfinement phase transition in hot β-stable hadronic matter. Assuming a first order phase transition, we calculate the enthalpy per baryon of the hadron–quark phase transition. We calculate and compare the nucleation rate and the nucleation time due to thermal and quantum nucleation mechanisms. We compute the crossover temperature above which thermal nucleation dominates the finite temperature quantum nucleation mechanism. We next discuss the consequences for the physics of proto-neutron stars. We introduce the concept of limiting conversion temperature and critical mass M_cr for proto-hadronic stars, and we show that proto-hadronic stars with a mass M<M_cr could survive the early stages of their evolution without decaying to a quark star.     

Quark matter and non-extensive thermodynamics

We investigate different ways of describing the thermodynamics of prehadronic matter in high-energy heavy-ion collisions. The non-extensive thermodynamics with certain assumptions enables an agreement between two important experimental facts. That cannot be achieved using the conventional Gibbs statistics. A massless quark-gluon plasma with E/N=1 GeV energy per particle and T=175 MeV spectral slope temperature can be assumed.     

Classical supersymmetric matter and cosmology

We show that supersymmetry may play an important role in giving a reasonable explanation of relevant cosmological features. We work in a classicalN=1 supergravity scenario showing that supersymmetric matter leads, in the classical limit, to a fluid model acting as the source of the gravitational field. The equation of state arises, in a natural way, as a consequence of the field equations. We study conditions for the matter dominated era and the existence of an inflationary solution. Using upper bounds of several red-shift experimental results we are able to give an estimate of the corresponding Hubble constant.     

Weylian dark matter and cosmology

The Weyl geometry, as modified by Dirac, can lead to the presence of a field consisting of bosons of spin 1 and finite mass. It was proposed earlier that these bosons, called weylons, form the bulk of the dark matter in the universe. The development of this Weylian dark matter is investigated from the time of its creation until the present, and an acceptable cosmological behavior is obtained. One finds that this dark matter was unimportant in the early stages of the universe but became important at the time of galaxy formation and may have played a role in this process.On leave from University of Haifa, School of Education of the Kibbutz Movement, Oranim, Tivon 36910, Israel.     

Quark condensate in the nuclear matter

We calculate the quark condensate in the nuclear matter, taking into account the single-pion and two-pion exchanges between nucleons. We find the dependence of the averaged value of the quark operator¯qq on the density of the matterρ. At very low density the nonlinear terms are proportional toρ ² and increase the tendency to restoration of the chiral symmetry. At larger values of density the account of interaction inside the matter slower down the restoration of chiral symmetry compared to the gas approximation law. The leading nonlinear term in Fermi momentum power expansion becomes of the orderρ ^4/3 . The value of the condensate at the saturation value of density is obtained. The role of multinucleon effects is analyzed.     

Nonsingular decaying-vacuum cosmology and baryonic matter

A nonsingular closed universe model with continuous creation of radiation or matter from the vacuum is introduced. Although primordial nucleosynthesis in this model follows the standard scenario it does not require the density of baryonic matter to be well below the critical density as in standard cosmology. The model predicts a present vacuum energy comparable with the matter energy. Its predictions for the classical low red-shift cosmological tests agree with the standard flat model results.     

Quantum cosmology with fermionic matter

The quantum evolution of homogeneous isotropic cosmological models with ferm ionic matter described by spinor fields is investigated within the framework of the formalism of superspace quantization. The fact that quadratic combinations of fermionic operators (current density, spin density, Lagrangian, etc.) are bosonic operators and admit an explicit Schrödinger representation is used in an essential way. It is shown that the DeWitt equation for the cosmological models with fermionic matter under consideration has the form of the Schrödinger equation, so that a correct definition is possible for the probability density of the existence of the models under consideration, in which the singularity is removed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 15–19, March, 1990.     

Quark matter conductivity in strong magnetic background

Applying the ideas and methods of condensed matter physics we calculate the quantum conductivity of quark matter in magnetic field. In strong field quantum conductivity is proportional to the square root of the field.     

Quark matter formation in dense stellar objects

It is expected that at very large densities and/or temperatures a quark-hadron phase transition takes place. Lattice QCD calculations at zero baryon density indicate that the transition occurs at T _c ∼ 150–170 MeV. The transition is likely to be second order or a cross over phenomenon. Although not much is known about the density at which the phase transition takes place at small temperatures, it is expected to occur around the nuclear densities of few times nuclear matter density. Also, there is a strong reason to believe that the quark matter formed after the phase transition is in colour superconducting phase. The matter densities in the interior of neutron stars being larger than the nuclear matter density, the neutron star cores may possibly consist of quark matter which may be formed during the collapse of supernova. Starting with the assumption that the quark matter, when formed consists of predominantly u and d quarks, we consider the evolution of s quarks by weak interactions in the present work. The reaction rates and time required to reach the chemical equilibrium are computed here. Our calculations show that the chemical equilibrium is reached in about 10⁻⁷ seconds. Further more during the equilibration process enormous amont of energy is released and copious numbers of neutrinos are produced. Implications of these on the evolution of supernovae will be discussed.