The role of an effective repulsive cosmological constant (a false vacuum or quintessence) in the very early inflationary expansion and the recent accelerated stage of our universe is reviewed, and it is shown that the relict cosmological constant can significantly influence accretion phenomena in recent universe.Je podán přehled role efektivní kosmologické konstanty (falešného vakua nebo kvintesence) ve velmi rané inflační expanzi a současné urychlené expanzi našeho vesmíru. Je ukázáno,že reliktní kosmologická konstanta může silně ovlivňovat akreční procesy v současné epoše evoluce vesmíru. IntroductionRecent cosmological observations suggest that immediately after the big bang our universe experienced an extremely accelerated inflationary expansion, while at the present era the universe entered a second stage of accelerated expansion [Wang et al., 2000]. The rate of present acceleration is many orders of magnitude smaller than during the inflation in the very early universe, i.e., we can call it a microinflationary expansion.The inflationary cosmology is the first theory within which it is possible to predict the structure of the universe on large scale, based on causal physics, representing thus a promising way for connecting fundamental physics with experiment. It enables a natural explanation for almost all of the problems of the standard cosmology [Linde, 1990]. Especially, the mechanism by which initial quantum vacuum fluctuations develop into the large scale structure of the universe is tested by recent observations in deep detail [Bahcall et al., 1999].Usually, the inflationary models assume that during inflation potential energy density of a scalar (inflaton) field φ dominates the energy-momentum tensor, T µν ∼ g µν V (φ), i.e., we must have slowly rolling inflaton field with 1 2φ 2 V (φ). The limiting caseφ = 0 corresponds to de Sitter space with a repulsive cosmological constant.The current accelerated expansion can be explained either by a positive vacuum energy V (cosmological constant), or by a slowly rolling, quintessential scalar field. The acceleration mechanism is the same for the inflaton and quintessential fields. The inflaton field decays giving rise to the standard decelerated expansion. The behavior of the quintessential field in future is the key to the fate of our universe. Inflationary cosmologyThe inflationary cosmology is based on the hypothesis that there was an extremely short time interval, just after the Big Bang, beginning at some time t i and ending at the 'reheating time' t R during which the scale 1

We study the cosmological evolution of scalar fields with arbitrary potentials in the presence of a baryotropic fluid ͑matter or radiation͒ without making any assumption on which term dominates. We determine what kind of potentials V() permits a quintessence interpretation of the scalar field and to obtain interesting cosmological results. We show that all model dependence is given in terms of ϵϪVЈ/V only and we study all possible asymptotic limits: approaching zero, a finite constant, or infinity. We determine the equation of state dynamically for each case. For the first class of potentials, the scalar field quickly dominates the universe behavior, with an inflationary equation of state allowing for a quintessence interpretation. The second case gives the extensively studied exponential potential, while in the last case, when approaches infinity, if it does not oscillate, then the energy density redshifts faster than the baryotropic fluid, but if oscillates, then the energy density redshift depends on the specific potential. PACS number͑s͒: 98.80.Cq, 95.35.ϩd, 98.80.Hw *

We study symmetry restoration at finite temperature in the theory of a charged scalar field interacting with a constant, external magnetic field. We compute the finite temperature effective potential including the contribution from ring diagrams. We show that in the weak field case, the presence of the field produces a stronger first order phase transition and that the temperature for the onset of the transition is lower, as compared to the case without magnetic field.

We study the symmetry breaking phenomenon in the standard model during the electroweak phase transition in the presence of a constant hypermagnetic field. We compute the finite temperature effective potential up to the contribution of ring diagrams in the weak field, high temperature limit and show that under these conditions, the phase transition becomes stronger first order.

Electrodynamics of charged scalar bosons and spin 1/2 fermions is studied at non-zero temperature, chemical potentials, and possible Bose condensate of the charged scalars. Debye screening length, plasma frequency, and the photon dispersion relation are calculated. It is found that in presence of the condensate the time-time component of the photon polarization operator in the first order in electric charge squared acquires infrared singular parts proportional to inverse powers of the spatial photon momentum k.

We study the structure and substructure of halos obtained in N-body simulations for a ÃCDM cosmology with non-Gaussian initial conditions. The initial statistics are lognormal in the gravitational potential field with positive (LN p ) and negative (LN n ) skewness; the sign of the skewness is conserved by the density field, and the power spectrum is the same for all the simulations. Our aim is not to test a given non-Gaussian statistics but to explore the generic effect of positive-and negative-skew statistics on halo properties. From our low-resolution simulations, we find that LN p (LN n ) halos are systematically more (less) concentrated than their Gaussian counterparts. This result is confirmed by our Milky Way-and cluster-sized halos resimulated with high resolution. In addition, they show inner density profiles that depend on the statistics: the innermost slopes of LN p (LN n ) halos are steeper (shallower) than those obtained from the corresponding Gaussian halos. A subhalo population embedded in LN p halos is more susceptible to destruction than its counterpart inside Gaussian halos. On the other hand, subhalos in LN n halos tend to survive longer than subhalos in Gaussian halos. The spin parameter probability distribution of LN p (LN n ) halos is skewed to smaller (larger) values with respect to the Gaussian case. Our results show how the statistics of the primordial density field can influence some halo properties, opening the possibility of constraining, albeit indirectly, the primordial statistics at small scales.

Screening of Coulomb field of test charge in plasma with Bose condensate of electrically charged scalar field is considered. It is found that the screened potential contains several different terms: one decreases as a power of distance (in contrast to the usual exponential Debye screening), some other oscillate with an exponentially decreasing envelope. Similar phenomenon exists for fermions (Friedel oscillations), but fermionic and bosonic systems have quite different features. Several limiting cases and values of the parameters are considered and the resulting potentials are presented.

The origin of the matter-antimatter asymmetry of the universe remains one of the outstanding questions yet to be answered by modern cosmology and also one of only a handful of problems where the need of a larger number of degrees of freedom than those contained in the standard model (SM) is better illustrated. An appealing scenario for the generation of baryon number is the electroweak phase transition that took place when the temperature of the universe was about 100 GeV. Though in the minimal version of the SM, and without considering the interaction of the SM particles with additional degrees of freedom, this scenario has been ruled out given the current bounds for the Higgs mass, this still remains an open possibility in supersymmetric extensions of the SM. In recent years it has also been realized that large scale magnetic fields could be of primordial origin. A natural question is what effect, if any, these fields could have played during the electroweak phase transition in connection to the generation of baryon number. Prior to the electroweak symmetry breaking, the magnetic modes able to propagate for large distances belonged to the U (1) group of hypercharge and hence receive the name of hypermagnetic fields. In this contribution, we summarize recent work aimed to explore the effects that these fields could have introduced during a first order electroweak phase transition. In particular, we show how these fields induce a CP asymmetric scattering of fermions off the true vacuum bubbles nucleated during the phase transition. The segregated axial charge acts as a seed for the generation of baryon number. We conclude by mentioning possible research venues to further explore the effects of large scale magnetic fields for the generation of the baryon asymmetry.