S.Yu. Khlebnikov
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Featured researches published by S.Yu. Khlebnikov.
Nuclear Physics | 1988
S.Yu. Khlebnikov; Mikhail E. Shaposhnikov
Abstract We present a non-equilibrium method for studying anomalous B -non-conservation in the electroweak theory at finite temperature. We derive formally the equation of B -evolution advocated previously on physical grounds. The kinetic coefficient in it is quite generally expressed through a thermodynamic average. This expression allows for an estimate of higher order corrections and is applicable both below and above the phase transition temperature.
Nuclear Physics | 1991
S.Yu. Khlebnikov; Valerii A. Rubakov; P.G. Tinyakov
Abstract We study the S-matrix and the total cross section of high-energy collisions in the one-instanton sector of purely bosonic theories with instantons. Making use of the coherent state formalism, we develop the perturbation theory around the instanton. We find that in the limit g2 → 0, E/Esph fixed, the leading behaviour of the total cross section is σtot ∼ exp[g−2(−2S0 + F(E/Esph))], where S0 is the instanton action. In the eelectroweak theory at E/Esph ⪡ 1, the function F(E/Esph) is determined by the gauge boson part of the instanton configuration and its explicit form is found. Our results suggest that there may exist a semiclassical type of procedure for evaluating the leading behaviour of the one-instanton total cross section at E≳Esph and g2 → 0.
Nuclear Physics | 1991
S.Yu. Khlebnikov; Valerii A. Rubakov; P.G. Tinyakov
Abstract We discuss the role of periodic euclidean solutions with two turning points and zero winding number (periodic instantons) in instanton-induced processes below the sphaleron energy E sph . We find that the periodic instantons describe certain multiparticle scattering events leading to the transitions between topologically distinct vacua. Both the semiclassical amplitudes and initial and final states of these transitions are determined by the periodic instantons. Furthermore, the corresponding probabilities are maximal among all states of a given energy. We show that at E ⪡ E sph , the periodic instantons can be approximated by infinite chains of ordinary instantons and anti-instantons, and they naturally emerge as deformations of the zero-energy instanton. In the framework of the two-dimensional abelian Higgs model and four-dimensional electroweak theory we show, however, that there is no obvious relation between periodic instantons and two-particle scattering amplitudes.
Nuclear Physics | 1990
A.I. Bochkarev; S.Yu. Khlebnikov; Mikhail E. Shaposhnikov
The effective action for the gauge fields in the electroweak plasma of the early Universe is considered. It is argued that in thermal equilibrium the effective action contains a CP-odd term proportional to the Chern-Simons number density provided the exactly conserved fermionic charges Li − Bnf are nonzero (Li are leptonic generations numbers, B is baryonic charge). In order to obtain the non-equilibrium distributions of fermions in the expanding Universe, the relevant kinetic equations involving both the electroweak CP-violation effects and the anomalous fermion number non-conservation are derived and solved. It is found that the Kobayashi-Maskawa CP-violation is sufficient to ensure the validity of the electroweak (EW) scenario of baryogenesis. We elaborate the program for the determination of the sign of the baryon asymmetry and discuss the interplay between GUT and EW scenarios.
Physics Letters B | 1991
S.Yu. Khlebnikov; Mikhail E. Shaposhnikov
Abstract We discuss the possibility of spontaneous parity violation in three-dimensional minkowskian and euclidean gauge theories with scalar fields. In perturbation theory, it is found that parity can be broken spontaneously only in the phase with restored gauge invariance, but is unbroken if the scalars have vacuum expectation values. We note that the spontaneous parity violation in the euclidean case may be related to the breaking of translational invariance. Implications of these results for high temperature gauge theories and cosmology are considered.
Modern Physics Letters A | 1990
S.Yu. Khlebnikov; Valerii A. Rubakov; P.G. Tinyakov
We study the total cross-section of high energy collisions in the one-instanton sector of purely bosonic theories with instantons. We find that in the limit g2 → 0, E/Esph = fixed, the leading behavior of the total cross-section is σlot ~ exp [1/g2(−2S0 + F(E/Esph))], where S0 is the instanton action. In the electroweak theory at E/Esph ≪ 1, the function F(E/Esph) is determined by the gauge boson part of the instanton configuration and its explicit form is found.
Physics Letters B | 1991
S.Yu. Khlebnikov; P.G. Tinyakov
Abstract We study the dependence of the final state exponential factor for the total instanton induced cross section on the constraints used to separate the instanton zero modes. We find the non-trivial dependence of the semiclassical exponent on the translational zero mode constraint, starting in the order (E E 0 ) 8 3 . We argue that, to compensate this dependence in the physical cross section, the hard-soft corrections should enter the exponent at this order. We identify the terms in the hard-soft gauge propagator which may give rise to such behaviour.
Nuclear Physics | 1990
S.Yu. Khlebnikov; Valerii A. Rubakov; P.G. Tinyakov
Abstract We study the instanton contribution to 2 n -particle cross section σ(2 → 2 n ) and to the inclusive cross section σ(2 →any) to the leading and next-to-leading orders in the semiclassical expansion, in the two-dimensional O(3) sigma model with explicit conformal symmetry breaking. The leading order instanton inclusive cross section increases exponentially with the c.m. energy √s and violates the unitary bound at √ s ∼ E sph , where E sph is the energy of the sphaleron in this model. The first correction becomes of the order of the leading term at lower energies √s ∼ gE sph , where g is the dimensionless coupling constant. Our results suggest that the semiclassical expansion for the inclusive baryon number violating cross section in the standard electroweak theory breaks down, due to the vector field pertubations around the instanton, at √ s of order of the Higgs vacuum expectation value, where the instanton cross section is still exponentially small. However, we present some arguments implying that the corrections to the leading order semiclassical result may sum up in such a way that the exponential growth of the cross section is not destroyed up to energies of order E sph .
Physics Letters B | 1988
S.Yu. Khlebnikov; Mikhail E. Shaposhnikov
Abstract We discuss the possibility that the strong CP problem is solved by raising the number of spatial dimensions a la Kaluza-Klein. We construct higher-dimensional manifolds which do not have the structure M4 × (compact space) where the θ-problem is absent, while locally the results of the standard dimensional reduction are reproduced.
Modern Physics Letters A | 1993
S.Yu. Khlebnikov
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 cutoff by pion mass, such clusters can still include sufficiently many particles to make the scaling observable.