arXiv subjects

A. D. Dolgov

Publications and source records attributed to A. D. Dolgov.

At least 163 records · Page 9Linked to original sources

arXiv1999

Neutrino oscillations in the early universe: How large lepton asymmetry can be generated?

The lepton asymmetry that could be generated in the early universe through oscillations of active to sterile neutrinos is calculated (almost) analytically for small mixing angles, sin 2θ< 10^{-2}. It is shown that for a mass squared difference, δm^2=-1 eV^2 it may rise at most by 6 orders of magnitude from the initial ``normal'' value of 10^{-10}, since the back-reaction from the refraction index terminates this rise while the asymmetry is still small. Only for very large mass differences, δm^2 about 10^9 eV^2, the lepton asymmetry could reach a significant magnitude exceeding 0.1.

hep-ph↗

arXiv1999

Impact of massive tau-neutrinos on primordial nucleosynthesis. Exact calculations

The influence of a massive Majorana tau-neutrino on primordial nucleosynthesis is rigorously calculated. The system of three integro-differential kinetic equations is solved numerically for the tau-neutrino mass in the interval from 0 to 20 MeV. It is found that the usual assumption of kinetic equilibrium is strongly violated and non-equilibrium corrections considerably amplify the effect. Even a very weak restriction from nucleosynthesis, allowing for one extra massless neutrino species, permits to conclude that m_ν_τ< 1 MeV. For a stricter bound, e.g. for dN < 0.3, the limit is m_ν_τ< 0.35 MeV.

hep-ph↗

arXiv1999

Unstable massive tau-neutrinos and primordial nucleosynthesis

The impact of unstable Majorana tau neutrinos on primordial nucleosynthesis is considered. The mass and lifetime of nu_tau are taken in the intervals 0.1-20 MeV and 0.001-400 sec respectively. The studied decay modes are nu_tau -> nu_mu + phi and nu_tau -> nu_e + phi, where phi is a massless (or light) scalar. Integro-differential kinetic equations are solved numerically without any simplifying assumptions. Our results deviate rather strongly from earlier calculations. Depending on mass, lifetime, and decay channels of the nu_tau, the number of effective neutrino species (found from He4), in addition to the 3 standard ones, varies from -2 to +2.5. The abundances of H2 and Li7 are also calculated.

hep-ph↗

arXiv1999

Neutrino Degeneracy and Chemically Inhomogeneous Universe

A possibility that the universe may be strongly inhomogeneous chemically, while very smooth energetically, is considered. A possible mechanism which could lead to such a picture is a large and inhomogeneous lepton asymmetry. The model may explain possibly observed variation of primordial deuterium by an order of magnitude and predicts helium-rich and possibly helium-poor regions where the helium mass fraction differs from the observed 25% by a factor of 2 in either direction. Helium variation can be observed by a different dumping rate of CMB angular spectrum at small angles at different patches of the sky.

astro-ph↗

arXiv1998

Equation of motion of a classical scalar field with back reaction of produced particles

In the one-loop approximation we derive the equation of motion for a classical scalar field ϕ_c (t) with the back reaction of particle production included. Renormalization of mass and couplings of ϕ_c is done explicitly. The equation is non-local in time, but can easily be treated perturbatively or numerically. For the weak trilinear coupling of the external field to the produced particles, the new equation gives the same solution as the familiar one with the Γϕ_c term. For a stronger coupling and other types of couplings the results are significantly different. The equation can be applied to the universe heating by the inflaton decay and to spontaneous baryogenesis.

hep-ph↗

arXiv1998

Superluminal propagation of light in gravitational field and non-causal signals

It has been found in several papers that, because of quantum corrections, light front can propagate with superluminal velocity in gravitational fields and even in flat space-time across two conducting plates. We show that, if this is the case, closed time-like trajectories would be possible and, in particular, in certain reference frames photons could return to their source of origin before they were produced there, in contrast to the opposite claim made in the literature.

gr-qc↗

arXiv1998

Nonequilibrium cosmic neutrinos and nucleosynthesis

The neutrino role in primordial nucleosynthesis is reviewed. The importance of nonequilibrium effects is emphasized both for the standard massless and possibly massive neutrinos. The upper bound on tau neutrino mass is presented. A spatial variation of primordial abundances and a possibility of observing them by precise measurements of the CMB anisotropy are considered.The nucleosynthesis bounds on the parameters of neutrino oscillations into sterile neutrinos are discussed.

astro-ph↗

arXiv1998

Classification of singular points in polarization field of CMB and eigenvectors of Stokes matrix

Analysis of the singularities of the polarization field of CMB, where polarization is equal to zero, is presented. It is found that the classification of the singular points differs from the usual three types known in the ordinary differential equations. The new statistical properties of polarization field are discussed, and new methods to detect the presence of primordial tensor perturbations are indicated.

astro-ph↗

arXiv1998

Nonequilibrium Corrections to the Spectra of Massless Neutrinos in the Early Universe - Addendum

We repeat our previous calculation of the spectrum distortion of massless neutrinos in the early universe with a considerably better accuracy and corrected for a missing numerical factor in one of the two ways of calculations presented in hep-ph/9703315. Now both ways of calculations are in perfect agreement and we essentially reproduce our old results presented in the abstract of the paper and used in the calculations of light element abundances. We disagree with the criticism of our calculations presented in astro-ph/9712199.

hep-ph↗

arXiv1998

Cosmology: Theory and Observations

The comparison of the Standard Cosmological Model (SCM) with astronomical observations, i.e. theory versus experiment, and with the Minimal Standard Model (MSM) in particle physics, i.e. theory versus theory, is discussed. The main issue of this talk is whether cosmology indicates new physics beyond the standard $SU(3)\times SU(2)\times U(1)$ model with minimal particle content. The answer to this question is strongly and definitely "YES". New, yet unknown, physics exists and cosmology presents very weighty arguments in its favor.

hep-ph↗

arXiv1997

Varying leptonic chemical potentials and spatial variation of primordial deuterium at high z

We try to explain the spatial variation of primordial deuterium suggested by some observations by varying leptonic chemical potentials. The variation of the latter may take place in some scenarios of leptogenesis. The model predicts a large mass fraction of $^4 He$ (35-60%) and $^7 Li$ (up to $10^{-9}$) in deuterium-rich regions. Because of lepton family symmetry, the angular variations of cosmic microwave background radiation can be sufficiently small although still observable in future measurements.

astro-ph↗

arXiv1997

Velocity of signal in attractive potential and propagation of light in gravitational field

The propagation of a massless field in attractive and repulsive potentials is considered. It is shown that though the group velocity in such potentials can be larger than one, the wave front propagates with the speed of light. A larger-than-one group velocity leads only to a strong deformation of the wave packet. The results obtained are applied to the light propagation in a gravitational field. An erroneous assertion concerning the last problem, recently made in the literature, is refuted.

hep-th↗

arXiv1997

The Problem of Vacuum Energy and Cosmology (A lecture presented at the 4th Colloque Cosmologie, Paris, June, 1997; to be published in the Proceedings)

Quantum field theory predicts that vacuum energy (or what is the same, cosmological constant) should be 50-100 orders of magnitude larger than the existing astronomical limit. A very brief review of possible solutions of this problem is presented. A mechanism of adjustment of vacuum energy down to (almost) zero by the back-reaction of massless vector or second rank tensor fields is discussed.

astro-ph↗

arXiv1997

Baryogenesis, 30 Years after

A review of the basic principles of baryogenesis is given. Baryogenesis in heavy particle decays as well as electroweak, SUSY-condensate, and spontaneous baryogenesis are discussed. The models of abundant creation of antimatter in the universe are briefly reviewed.

hep-ph↗

arXiv1997

Primordial Nucleosynthesis, Majorons and Heavy Tau Neutrinos

We determine the restrictions imposed by primordial nucleosynthesis upon a heavy tau neutrino, in the presence of nu-tau annihilations into Majorons, as expected in a wide class of particle physics models of neutrino mass. We determine the equivalent number of light neutrino species $N_{eq}$ as a function of nu-tau mass and the nu-tau-Majoron coupling $g$. We show that for theoretically plausible $g$ values $\gsim 10^{-4}$ present nucleosynthesis observations can not rule out nu-tau masses in the MeV range. Moreover, these models give $N_{eq} \leq 3$ in the nu-tau mass region 1-10 MeV, for very reasonable values of $g \geq 3 \times 10^{-4}$. The evasion of the cosmological limits brings new interest to the improvement of the present laboratory limit on the nu-tau mass which can be achieved at a tau-charm factory.

hep-ph↗

arXiv1997

Nonequilibrium Corrections to the Spectra of Massless Neutrinos in the Early Universe

Distortion of the equilibrium spectra of cosmic neutrinos due to interaction with hotter electrons and positrons in the primeval cosmic plasma is considered. The set of integro-differential kinetic equations for neutrinos is accurately numerically solved. The relative corrections to neutrino energy densities are approximately 0.9% for $ν_e$ and 0.4% for $ν_μ$ and $ν_τ$. This effect results in $1.4 \cdot 10^{-4}$ increase in the primordial $^4 He$ abundance.

hep-ph↗

arXiv1997

Instructive Properties of Quantized Gravitating Dust Shell

We investigate quantum dynamics of self-gravitating spherical dust shell. The wave functions of discrete spectrum are not localized inside the Schwarzschild radius. We argue that such shells can transform into white holes (in another space). It is plausible that shells with bare masses larger than the Planck mass loose their mass emitting lighter shells.

hep-th↗

arXiv1997

Do muons oscillate ?

We develop a theory of the EPR-like effects due to neutrino oscillations in the $π\to μν$ decays. Its experimental implications are space-time correlations of neutrino and muon when they are both detected, while the pion decay point is not fixed. However, the more radical possibility of muon oscillations in experiments where only muons are detected (as it has been suggested in hep-ph/9509261), is ruled out. We start by discussing decays of monochromatic pions, and point out a few ``paradoxes''. Then we consider pion wave packets, solve the ``paradoxes'', and show that the formulas for $μnu$ correlations can be transformed into the usual expressions, describing neutrino oscillations, as soon as the pion decay point is fixed.

hep-ph↗