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M. Shaposhnikov

Publications and source records attributed to M. Shaposhnikov.

At least 37 records · Page 2Linked to original sources
arXiv2005

Can an odd number of fermions be created due to chiral anomaly?

We describe a possibility of creation of an odd number of fractionally charged fermions in 1+1 dimensional Abelian Higgs model. We point out that for 1+1 dimensions this process does not violate any symmetries of the theory, nor makes it mathematically inconsistent. We construct the proper definition of the fermionic determinant in this model and underline its non-trivial features that are of importance for realistic 3+1 dimensional models with fermion number violation.

hep-th↗
arXiv2005

The fate of the zero mode of the five-dimensional kink in the presence of gravity

We investigate what becomes of the translational zero-mode of a five-dimensional domain wall in the presence of gravity, studying the scalar perturbations of a thick gravitating domain wall with AdS asymptotics and a well-defined zero-gravity limit. Our analysis reveals the presence of a wide resonance which can be seen as a remnant of the translational zero-mode present in the domain wall in the absence of gravity and which ensures a continuous change of the physical quantities (such as e.g. static potential between sources) when the Planck mass is sent to infinity. Provided that the thickness of the wall is much smaller than the AdS radius of the space-time, the parameters of this resonance do not depend on details of the domain wall's structure, but solely on the geometry of the space-time.

hep-th↗
arXiv2005

One-loop fermionic corrections to the instanton transition in two dimensional chiral Higgs model

The one-loop fermionic contribution to the probability of an instanton transition with fermion number violation is calculated in the chiral Abelian Higgs model in 1+1 dimensions, where the fermions have a Yukawa coupling to the scalar field. The dependence of the determinant on fermionic, scalar and vector mass is determined. We show in detail how to renormalize the fermionic determinant in partial wave analysis, which is convenient for computations.

hep-ph↗
arXiv2004

Brane-worlds and theta-vacua

Reductions from odd to even dimensionalities ($5\to 4$ or $3\to 2$), for which the effective low-energy theory contains chiral fermions, present us with a mismatch between ultraviolet and infrared anomalies. This applies to both local (gauge) and global currents; here we consider the latter case. We show that the mismatch can be explained by taking into account a change in the spectral asymmetry of the massive modes--an odd-dimensional analog of the phenomenon described by the Atiyah-Patodi-Singer theorem in even dimensionalities. The result has phenomenological implications: we present a scenario in which a QCD-like $θ$-angle relaxes to zero on a certain (possibly, cosmological) timescale, despite the absence of any light axion-like particle.

hep-th↗
arXiv2004

Quasilocalized gravity without asymptotic flatness

We present a toy model of a generic five-dimensional warped geometry in which the 4D graviton is not fully localized on the brane. Studying the tensor sector of metric perturbation around this background, we find that its contribution to the effective gravitational potential is of 4D type (1/r) at the intermediate scales and that at the large scales it becomes 1/r^{1+alpha}, 0<alpha=< 1 being a function of the parameters of the model (alpha=1 corresponds to the asymptotically flat geometry). Large-distance behavior of the potential is therefore not necessarily five-dimensional. Our analysis applies also to the case of quasilocalized massless particles other than graviton.

hep-th↗
arXiv2004

Einstein static universe as a brane in extra dimensions

We present a brane-world scenario in which two regions of $AdS_5$ space-time are glued together along a 3-brane with constant positive curvature such that {\em all} spatial dimensions form a compact manifold of topology $S^4$. It turns out that the induced geometry on the brane is given by Einstein's static universe. It is possible to achieve an anisotropy of the manifold which allows for a huge hierarchy between the size of the extra dimension $R$ and the size of the observable universe $R_U$ at present. This anisotropy is also at the origin of a very peculiar property of our model: the physical distance between {\em any two points} on the brane is of the order of the size of the extra dimension $R$ regardless of their distance measured with the use of the induced metric on the brane. In an intermediate distance regime $R \ll r \ll R_U$ gravity on the brane is shown to be effectively 4-dimensional, with corresponding large distance corrections, in complete analogy with the Randall-Sundrum II model. For very large distances $r \sim R_U$ we recover gravity in Einstein's static universe. However, in contrast to the Randall-Sundrum II model the difference in topology has the advantage of giving rise to a geodesically complete space.

hep-th↗
arXiv2004

Effective gauge theories on domain walls via bulk confinement?

We study with lattice techniques the localisation of gauge fields on domain wall defects in 2+1 dimensions, following a scenario originally proposed by Dvali and Shifman for 3+1 dimensions, based on confining dynamics in the bulk. We find that a localised gauge zero-mode does exist, if the domain wall is wide enough compared with the confinement scale in the bulk. The range of applicability of the corresponding low-energy effective theory is determined by the mass gap to the higher modes. For a wide domain wall, this mass gap is set by ``Kaluza--Klein modes'' as determined by the width. It is pointed out that in this regime the dynamical energy scales generated by the interactions of the localised zero-modes are in fact higher than the mass gap. Therefore, at least in 2+1 dimensions, the zero-modes alone do not form a low-energy effective gauge theory of a traditional type. Finally, we discuss how the situation is expected to change in going to 3+1 dimensions.

hep-ph↗
arXiv2003

Localisation and mass generation for non-Abelian gauge fields

It has been suggested recently that in the presence of suitably "warped" extra dimensions, the low-energy limit of pure gauge field theory may contain massive elementary vector bosons localised on a "brane", but no elementary Higgs scalars. We provide non-perturbative evidence in favour of this conjecture through numerical lattice measurements of the static quark-antiquark force of pure SU(2) gauge theory in three dimensions, of which one is warped. We consider also warpings leading to massless localised vector bosons, and again find evidence supporting the perturbative prediction, even though the gauge coupling diverges far from the brane in this case.

hep-ph↗
arXiv2002

Warped compactification on Abelian vortex in six dimensions

We consider the possibility of localizing gravity on a Nielsen-Olesen vortex in the context of the Abelian Higgs model. The vortex lives in a six-dimensional space-time with negative bulk cosmological constant. In this model we find a region of the parameter space leading, simultaneously, to warped compactification and to regular space-time geometry. A thin defect limit is studied. Regular solutions describing warped compactifications in the case of higher winding number are also presented.

hep-th↗
arXiv2000

Primordial magnetic fields from inflation?

The hot plasma above the electroweak scale contains (hyper) charged scalar particles which are coupled to Abelian gauge fields. Scalars may interact with gravity in a non-conformally invariant way and thus their fluctuations can be amplified during inflation. These fluctuations lead to creation of electric currents and produce inhomogeneous distribution of charge density, resulting in the generation of cosmological magnetic fields. We address the question whether these fields can be coherent at large scales so that they may seed the galactic magnetic fields. Depending upon the mass of the charged scalar and upon various cosmological (critical fraction of energy density in matter, Hubble constant) and particle physics parameters we found that the magnetic fields generated in this way are much larger than vacuum fluctuations. However, their amplitude on cosmological distances is found to be too small for seeding the galactic magnetic fields.

hep-ph↗
arXiv1999

An all-order discontinuity at the electroweak phase transition

We define a non-local gauge-invariant Green's function which can distinguish between the symmetric (confinement) and broken (Higgs) phases of the hot SU(2)xU(1) electroweak theory to all orders in the perturbative expansion. It is related to the coupling of the Chern-Simons number to a massless Abelian gauge field. The result implies either that there is a way to distinguish between the phases, even though the macroscopic thermodynamical properties of the system have been observed to be smoothly connected, or that the perturbative Coleman-Hill theorem on which the argument is based, is circumvented by non-perturbative effects. We point out that this question could in principle be studied with three-dimensional lattice simulations.

hep-th↗
arXiv1998

The Electroweak Phase Transition in a Magnetic Field

We study the finite temperature electroweak phase transition in an external hypercharge U(1) magnetic field H_Y, using lattice Monte Carlo simulations. For sufficiently small fields, H_Y/T^2 < 0.3, the magnetic field makes the first order transition stronger, but it still turns into a crossover for Higgs masses m_H ~ 80 GeV. For larger fields, we observe a mixed phase analogous to a type I superconductor, where a single macroscopic tube of the symmetric phase, parallel to H_Y, penetrates through the broken phase. For the magnetic fields and Higgs masses studied, we did not see indications of the expected Ambjorn-Olesen phase, which should be similar to a type II superconductor.

hep-lat↗
arXiv1998

The universal properties of the electroweak phase transition

The first order electroweak phase transition in the Standard Model turns into a regular cross-over at a critical Higgs mass m_{H,c} approximately 75 GeV. At the critical point the transition is of second order. We make a detailed investigation of the critical properties of the electroweak theory at the critical point, and we find that the transition falls into the 3d Ising universality class. The continuum limit extrapolation of the critical Higgs mass is m_{H,c} = 72(2) GeV, which implies that there is no electroweak phase transition in the Standard Model.

hep-ph↗
arXiv1998

The Ising model universality of the electroweak theory

Lattice simulations have shown that the first order electroweak phase transition turns into a regular cross-over at a critical Higgs mass m_{H,c}. We have developed a method which enables us to make a detailed investigation of the critical properties of the electroweak theory at m_{H,c}. We find that the transition falls into the 3d Ising universality class. The continuum limit extrapolation of the critical Higgs mass is m_{H,c} = 72(2) GeV, which implies that there is no electroweak phase transition in the Standard Model.

hep-lat↗
arXiv1998

The universality class of the electroweak theory

We study the universality class and critical properties of the electroweak theory at finite temperature. Such critical behaviour is found near the endpoint m_H=m_{H,c} of the line of first order electroweak phase transitions in a wide class of theories, including the Standard Model (SM) and a part of the parameter space of the Minimal Sypersymmetric Standard Model (MSSM). We find that the location of the endpoint corresponds to the Higgs mass m_{H,c} = 72(2) GeV in the SM with sin^2 theta_W = 0, and m_{H,c} < 80 GeV with sin^2 theta_W = 0.23. As experimentally m_H > 88 GeV, there is no electroweak phase transition in the SM. We compute the corresponding critical indices and provide strong evidence that the phase transitions near the endpoint fall into the three dimensional Ising universality class.

hep-lat↗
arXiv1998

Thermodynamics of Non-Topological Solitons

In theories with low energy supersymmetry breaking, the effective potential for squarks and sleptons has generically nearly flat directions, V(phi) ~ M^4 (log(phi/M))^n. This guarantees the existence of stable non-topological solitons, Q-balls, that carry large baryon number, B >> (M/m_p)^4, where m_p is the proton mass. We study the behaviour of these objects in a high temperature plasma. We show that in an infinitely extended system with a finite density of the baryon charge, the equilibrium state is not homogeneous and contains Q-balls at any temperature. In a system with a finite volume, Q-balls evaporate at a volume dependent temperature. In the cosmological context, we formulate the conditions under which Q-balls, produced in the Early Universe, survive till the present time. Finally, we estimate the baryon to cold dark matter ratio in a cosmological scenario in which Q-balls are responsible for both the net baryon number of the Universe and its dark matter. We find out naturally the correct orders of magnitude for M ~ 1...10 TeV: η~ 10^{-10} (M/TeV)^{-2} (B/10^{26})^{-1/2}.

hep-ph↗
arXiv1997

High Temperature Dimensional Reduction and Parity Violation

The effective super-renormalizable 3-dimensional Lagrangian, describing the high temperature limit of chiral gauge theories, has more symmetry than the original 4d Lagrangian: parity violation is absent. Parity violation appears in the 3d theory only through higher-dimensional operators. We compute the coefficients of dominant P-odd operators in the Standard Electroweak theory and discuss their implications. We also clarify the parametric accuracy obtained with dimensional reduction.

hep-ph↗