The Weinberg-Salam model and early cosmology

The consequences for cosmology of the phase transition in which SU(2)×U(1) symmetry is broken in the Weinberg-Salam model are discussed. The qualitative arguments concerning the effect of the phase transition on the baryon-to-entropy ratio that were recently posed by Witten for the case of a Coleman-Weinberg light Higgs boson are confirmed through exact numerical computations, but some quantitative disagreement is found. The computations are extended to the case in which the light Higgs boson is not of the Coleman-Weinberg type and the nature of the phase transition is discussed. Other cosmological effects are considered.     

Bulk viscous cosmology in early Universe

The effect of bulk viscosity on the early evolution of Universe for a spatially homogeneous and isotropic Robertson-Walker model is considered. Einstein’s field equations are solved by using ‘gamma-law’ equation of state p = (γ − 1)ρ, where the adiabatic parameter gamma (γ) depends on the scale factor of the model. The ‘gamma’ function is defined in such a way that it describes a unified solution of early evolution of the Universe for inflationary and radiation-dominated phases. The fluid has only bulk viscous term and the coefficient of bulk viscosity is taken to be proportional to some power function of the energy density. The complete general solutions have been given through three cases. For flat space, power-law as well as exponential solutions are found. The problem of how the introduction of viscosity affects the appearance of singularity, is briefly discussed in particular solutions. The deceleration parameter has a freedom to vary with the scale factor of the model, which describes the accelerating expansion of the Universe.      

The phase structure in the Coleman-Weinberg theory

We study the phase structure in the minimal SU(5)-Coleman-Weinberg theory. We consider the implication of the results for cosmology and point out that the Higgs coupling constant must be fine-tuned in order to realize the new inflationary universe scenario. The effects of heavy fermions are also discussed.     

Coleman-Weinberg approach in distorted space-time

The Coleman-Weinberg approach (renormalization-group improvement of the effective potential) is developed for an arbitrary renormalizable massless theory in distorted space-time. Some explicit examples are considered. It is proven that a phase transition induced by nonzero curvature may occur in an SU(5) inflationary universe.Tomsk Pedagogical Institute. Universal of Barcelona. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 28–32, January, 1994.     

Quantum ekpyrotic mechanism in Fermi-bounce curvaton cosmology

Within the context of the Fermi-bounce curvaton mechanism, we analyze the one-loop radiative corrections to the four-fermion interaction, generated by the non-dynamical torsion field in the Einstein-Cartan-Holst-Sciama-Kibble theory. We show that contributions that arise from the one-loop radiative corrections modify the energy-momentum tensor, mimicking an effective Ekpyrotic fluid contribution. Therefore, we call this effect quantum Ekpyrotic mechanism. This leads to the dynamical washing out of anisotropic contributions to the energy-momentum tensor, without introducing any new extra Ekpyrotic fluid. We discuss the stability of the bouncing mechanism and derive the renormalization group flow of the dimensional coupling constant ξ, checking whether any change of its sign takes place towards the bounce. This enforces the theoretical motivations in favor of the torsion curvaton bounce cosmology as an alternative candidate to the inflation paradigm.     

New gravitational tests of early universe cosmology

Gravitational waves and lenses were among the earliest predictions of general relativity. I demonstrate here how both these phenomena can, in conjunction with newly discovered astrophysical objects, be used to test fundamental aspects of early universe cosmology, including (a) scenarios for galaxy formation, and (b) nonadiabatic expansion before and after nucleosynthesis.Research supported in part by the N.S.F. under Grant No. PHY-82-15249.     

Vector tadpole graphs in the Coleman-Weinberg model

In the Coleman-Weinberg model (massless scalar quantum electrodynamics), a gauge invariant approximation scheme is obtained by summing vector tadpole graphs to all loop orders. We investigate the influence of this summation on the masses of the scalar and vector particles in the model.     

Coleman-Weinberg,Nielsen and Daisies

In a recent paper, Nielsen suggested a method for obtaining higher-order corrections in the Coleman-Weinberg model. We show a simple explicit calculation that this is consistent with his identities and corresponds, as he noted, to a “daisy” expansion.     

Neumann Boundary Conditions Inhibiting SSB in Coleman-Weinberg Mechanism

In this work we show that homogeneous Neumann boundary conditions inhibit the Coleman-Weinberg mechanism for spontaneous symmetry breaking in the scalar electrodynamics if the length of the finite region is small enough （a = e2Mφ-1, where M, is the mass of the scalar field generated by the Coleman-Weinberg mechanism）.     

Bubble nucleation and the Coleman-Weinberg model

Motivated by the “new inflationary universe scenario”, we have made a detailed study of the bubble nucleation process in (nearly) Coleman-Weinberg models with small positive scalar field mass terms. Our goal has been to show the consistency and interrelation between Coleman's analysis of bubble nucleation in flat space, the work of Coleman and De Luccia on bubble nucleation with gravitational effects and the recent dramatically different results of Hawking and Moss on bubble nucleation in Coleman-Weinberg models in a de Sitter background. Many of our results apply to more general classes of potentials.     

Neumann Boundary Conditions Inhibiting SSB in Coleman-Weinberg Mechanism

In this work we show that homogeneous Neumann boundary conditionsinhibit the Coleman-Weinberg mechanism for spontaneous symmetry breakingin the scalar electrodynamics if the length of the finite region is small enough (a = e²M^-1_φ, where M_φ is the mass of the scalar field generated by the Coleman-Weinberg mechanism).     

The horizon problem in Friedmann-Robertson-Walker cosmology

The horizon problem is studied in the Friedmann-Robertson-Walker (FEW) models. The exact condition for which an observer does not have the horizon problem for a hypersurfacet = constant is derived first in terms of the redshift, then in terms of the temperature which is an observer-independent parameter. It is shown that there are no values of the deceleration parameterq _o that solve the problem for the recombination hypersurface, while the usual approximated way to investigate this problem leads to a very small positive value of qo — Moreover, the temperature parameter allows us to show when the horizon problem arises and afterwards increases with time. Not being restricted to the Cosmic Microwave Background (CMB) case, its evolution ought to be considered when searching for a possible solution.     

Coleman-Weinberg theory and the new inflationary universe scenario

It is argued that a new inflationary universe scenario, which provides a possible solution of the horizon, flatness, homogeneity, isotropy and primordial monopole problems, can be naturally implemented in the context of grand unified theories of the type of the Coleman-Weinberg theory.     

The cosmology of decaying gravitinos

We consider the cosmological constraints on unstable particles with masses O(m_W). Constraints from the energy density during primordial nucleosynthesis, from subsequent entropy generation, and from perturbations of the microwave background are not as restrictive as bounds from the dissociation of light elements. Most restrictive is the need to avoid over-production of D and ³He through the photo-dissociation of ⁴He. When applied to gravitinos, this bound imposes an upper limit of O(10⁸) GeV on the reheating temperature after inflation, which could create problems for baryosynthesis in supersymmetric theories. These problems can be avoided if the photino is heavier than the gravitino.     

The pre-big bang scenario in string cosmology

We review physical motivations, phenomenological consequences, and open problems of the so-called pre-big bang scenario in superstring cosmology.     

The quantum cosmology in the Brans-Dicke theory

In this paper, we try to establish the quantum cosmology based on the Brans-Dicke gravitational theory. The most remarkable property of it is that the scale factora(t) has a lower limit, where the cosmological wave function approaches zero.