arXiv subjects

S. Yu. Khlebnikov

Publications and source records attributed to S. Yu. Khlebnikov.

12 recordsLinked to original sources

arXiv1997

Resonant decay of Bose condensates

We present results of fully non-linear calculations of decay of the inflaton interacting with another scalar field X. Combining numerical results for cosmologically interesting range of resonance parameter, q \leq 10^6, with analytical estimates, we extrapolate them to larger q. We find that scattering of X fluctuations off the Bose condensate is a very efficient mechanism limiting growth of X fluctuations. For a single-component X, the resulting variance, at large q, is much smaller than that obtained in the Hartree approximation.

hep-ph↗

arXiv1997

Relic gravitational waves produced after preheating

We show that gravitational radiation is produced quite efficiently in interactions of classical waves created by resonant decay of a coherently oscillating field. For simple models of chaotic inflation in which the inflaton interacts with another scalar field, we find that today's ratio of energy density in gravitational waves per octave to the critical density of the universe can be as large as 10^{-12} at the maximal wavelength of order 10^{5} cm. In the pure $λϕ^4$ model, the maximal today's wavelength of gravitational waves produced by this mechanism is of order 10^6 cm, close to the upper bound of operational LIGO and TIGA frequencies. The energy density of waves in this model, though, is likely to be well below the sensitivity of LIGO or TIGA at such frequencies. We discuss possibility that in other inflationary models interaction of classical waves can lead to an even stronger gravitational radiation background.

hep-ph↗

arXiv1996

The Universe after inflation: the wide resonance case

We study numerically the decay of massive and massless inflatons into massive excitations, via a $ϕ^2 X^2$ coupling, in the expanding Universe. We find that a wide enough resonance can survive the Universe expansion, though account for the expansion is very important for determining precisely how wide it should be. For a massive inflaton, the effective production of particles with mass ten times that of the inflaton requires very large values of the resonance parameter $q$, $q\gsim 10^8$. For these large $q$, the maximal size of produced fluctuations is significantly suppressed by the back reaction, but at least within the Hartree approximation they are still not negligible. For the massless inflaton with a $λϕ^4/4$ potential, the Universe expansion completely prevents a resonance production of particles with masses larger than $\sqrtλϕ(0)$ for $q$ up to $q=10^6$.

hep-ph↗

arXiv1996

Melting of the Higgs Vacuum: Conserved Numbers at High Temperature

We discuss the computation of the grand canonical partition sum describing hot matter in systems with the Higgs mechanism in the presence of non-zero conserved global charges. We formulate a set of simple rules for that computation in the high-temperature approximation in the limit of small chemical potentials. As an illustration of the use of these rules, we calculate the leading term in the free energy of the standard model as a function of baryon number B. We show that this quantity depends continuously on the Higgs expectation value $ϕ$, with a crossover at $ϕ\sim T$ where Debye screening overtakes the Higgs mechanism---the Higgs vacuum ``melts". A number of confusions that exist in the literature regarding the B dependence of the free energy is clarified.

hep-ph↗

arXiv1996

Classical decay of inflaton

We present the first fully non-linear calculation of inflaton decay. We map inflaton decay onto an equivalent classical problem and solve the latter numerically. In the $λϕ^4$ model, we find that parametric resonance develops slower and ends at smaller values of fluctuating fields, as compared to estimates existing in literature. We also observe a number of qualitatively new phenomena, including a stage of semiclassical thermalization, during which the decay of inflaton is essentially as effective as during the resonance stage.

hep-ph↗

arXiv1995

Strong-coupling expansions for chiral models of electroweak symmetry breaking

We consider chiral $U(N)\times U(N)$ models with fermions in the limit of infinitely large local bare Yukawa coupling. When the scalar field is subject to non-linear constraint, phase transitions in these models are seen to be identical to those in the corresponding purely bosonic ones. Relaxing the non-linear constraint, we compute the seventh-order strong-coupling series for the susceptibility in these models and analyze them numerically for the $U(2)\times U(2)$ case. We find that in four dimensions the approach to the phase transition follows to a good accuracy the mean-field critical behavior, indicating the absence of non-trivial fixed points at strong coupling and being consistent with the first-order nature of the transition. In three dimensions, the strongly-coupled bosonic $U(2)\times U(2)$ model (without gauge fields) has a first-order transition strong enough to accommodate electroweak baryogenesis only for a narrow region of the bare parameter space.

hep-ph↗

arXiv1994

The current of fermions scattered off a bubble wall

Proceeding from WKB quantization conditions, we derive a semiclassical expression for the current of fermions scattered off a propagating bubble wall in the presence of longitudinal gauge field. It agrees with the expression used by Nasser and Turok in semiclassical analysis of instability of electroweak bubble walls with respect to longitudinal $Z$ condensation. We discuss the resulting dispersion relation for longitudinal $Z$ field and show that light species are important for the analysis of stability, because of their large contribution to plasma frequency.

hep-ph↗

arXiv1994

Semiclassical transition probabilities for interacting oscillators

Semiclassical transition probabilities characterize transfer of energy between "hard" and "soft" modes in various physical systems. We establish the boundary problem for singular euclidean solutions used to calculate such probabilities. Solutions are found numerically for a system of two interacting quartic oscillators. In the double-well case, we find numerical evidence that certain regular {\em minkowskian} trajectories have approximate stopping points or, equivalently, are approximately periodic. This property leads to estimates of tunneling excitation probabilities in that system and suggests that similar estimates may be possible in other systems with tunneling.

hep-ph↗

arXiv1993

Effective action of magnetic monopole in three-dimensional electrodynamics with massless matter and gauge theories of superconductivity

We compute one-loop effective action of magnetic monopole in three-dimensional electrodynamics of massless bosons and fermions and find that it contains an infrared logarithm. So, when the number of massless matter species is sufficiently large, monopoles are suppressed and in the weak coupling limit charged particles are unconfined. This result provides some support to gauge theories of high-temperature superconductors. It also provides a mechanism by which interlayer tunneling of excitations with one unit of the ordinary electric charge can be suppressed while that of a doubly charged object is allowed.

hep-ph↗

arXiv1993

Strongly interacting $W$ bosons and supersymmetry

We present arguments in favor of the idea that supersymmetric sigma models with compact symmetric Kähler spaces as target manifolds have a second-order phase transition in four dimensions. When applied to electroweak symmetry breaking, these models then do not require a light Higgs boson or techni-resonances but predict fermionic superpartners of longitudinal W's and Z with masses at or below TeV scale. Presence of the phase transition leads to a fractional-power energy dependence of fixed-angle scattering amplitude of longitudinal W's and Z's at high energies.

hep-ph↗

arXiv1993

Disoriented chiral condensate in (1+1) Lorentz-invariant geometry

We consider isospin correlations of pions produced in a relativistic nuclear collision, using an effective theory of the chiral order parameter. Our theory has (1+1) Lorentz invariance as appropriate for the central rapidity region. We argue that in certain regions of space correlations of the chiral order parameter are described by the fixed point of the (1+1) WZNW model. The corresponding anomalous dimension determines scaling of the probability to observe a correlated cluster of pions with the size of this cluster in rapidity. Though the maximal size of clusters for which this scaling is applicable is cut off by pion mass, such clusters can still include sufficiently many particles to make the scaling observable.

hep-ph↗

arXiv1992

Light fermions in composite models

In preon models based on chiral gauge theories, we show that light composite fermions can ensue as a result of gauging a subset of preons in a vector-like manner. After demonstrating how this mechanism works in a toy example, we construct a one generation model of quarks which admits a hierarchy between the up and down quark masses as well as between these masses and the compositeness scale. In simple extensions of this model to more generations we discuss the challenges of obtaining any quark mixing. Some possible phenomenological implications of scenarios where quarks and leptons which are heavier are also less pointlike are also considered.

hep-ph↗