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K. G. Klimenko

Publications and source records attributed to K. G. Klimenko.

At least 55 records · Page 3Linked to original sources
arXiv2013

Superconductivity phenomenon induced by external in-plane magnetic field in (2+1)-dimensional Gross--Neveu type model

Phase structure of the (2+1)-dimensional model with four-fermion interaction of spin-1/2 quasiparticles (electrons) both in the fermion-antifermion (or chiral) and fermion-fermion (or superconducting) channels is considered at nonzero chemical potential $μ$ and under the influence of an in-plane, i.e. parallel to a system sheet, external magnetic field $\vec B_\parallel$. It is shown that at sufficiently large values of $μ$ and/or $\vec B_\parallel$ the Cooper pairing (or superconducting) phase appears in the system at arbitrary relation between coupling constants, provided that there is an (arbitrary small) attractive interaction in the superconducting channel. In particular, at sufficiently weak attractive interaction in the chiral channel, the Cooper pairing occurs even at infinitesimal values of $μ$ and/or $\vec B_\parallel$. The superconducting phase of the model is always a paramagnetic one.

hep-th↗
arXiv2012

Superconducting phase transitions induced by chemical potential in (2+1)-dimensional four-fermion quantum field theory

In the paper a generalization of the (1+1)-dimensional model by Chodos et al [Phys. Rev. D61, 045011 (2000)] has been performed to the case of (2+1)-dimensional spacetime. The model includes four-fermion interaction both in the fermion-antifermion (or chiral) and fermion-fermion (or superconducting) channels. We study temperature $T$ and chemical potential $μ$ induced phase transitions in the leading order of large-$N$ expansion technique, where $N$ is a number of fermion fields. It is shown that at sufficiently large values of $μ$ and arbitrary relations between coupling constants, superconducting phase appears in the system both at T=0 and $T>0$. In particular, at T=0 and sufficiently weak attractive interaction in the chiral channel, the Cooper pairing occurs for arbitrary couplings in the superconducting channel even at infinitesimal values of $μ$.

hep-th↗
arXiv2012

Inhomogeneous charged pion condensation phenomenon in the NJL$_2$ model with quark number and isospin chemical potentials

The properties of two-flavored massive Nambu--Jona-Lasinio model in (1+1)-dimensional spacetime are investigated in the presence of isospin and quark number chemical potentials. The consideration is performed in the large-$N_c$ limit, where $N_c$ is the number of colored quarks. It is shown in the framework of this model that charged pion condensation phenomenon of dense quark/hadron isotopically asymmetric matter is rather a spatially inhomogeneous than a homogeneous one.

hep-ph↗
arXiv2011

Chiral density waves in the NJL$_2$ model with quark number and isospin chemical potentials

We investigate the phase portrait of the (1+1)-dimensional massless two-flavored NJL$_2$ model containing a quark number chemical potential $μ$ and an isospin chemical potential $μ_I$ in the limit of a large number of colors $N_c\to\infty$. Particular attention is paid to the question to what extent the inclusion of an isospin asymmetry affects chiral condensates to have a spatial inhomogeneity in the form of the so-called chiral density waves (CDW) (chiral spirals). It is shown that at zero temperature and comparatively small values of $μ$, i.e. at $μ<μ_c\approx 0.68M_0$ ($M_0$ is the dynamical quark mass in the vacuum) only the homogeneous charged pion condensation phase is realized for arbitrary nonzero values of $μ_I$. Contrary to this, for large values of $μ>μ_c$, two CDW phases appear in the $(μ_I,μ)$-phase diagram of the model. In the first phase, CDWs are clockwise twisted chiral spirals and in the second phase they are counterclockwise. The influence of nonzero temperature on the formation of the CDW phases is also investigated.

hep-ph↗
arXiv2011

Finite-size effects in pion condensation phenomena of dense baryonic matter in the NJL$_2$ model

The properties of two-flavored massless Nambu-Jona-Lasinio model in (1+1)-dimensional $R^1\times S^1$ spacetime with compactified space coordinate are investigated in the presence of isospin and quark number chemical potentials $μ_I$, $μ$. The consideration is performed in the large $N_c$ limit, where $N_c$ is the number of colored quarks. It is shown that at $L=\infty$ ($L$ is the length of the circumference $S^1$) the pion condensation (PC) phase with {\it zero quark number density} is realized at arbitrary nonzero $μ_I$ and for rather small values of $μ$. However, at arbitrary finite values of $L$ the phase portrait of the model contains the PC phase with {\it nonzero quark number density} (in the case of periodic boundary conditions for quark fields). Hence, finite sizes of the system can serve as a factor promoting the appearance of the PC phase in quark matter with nonzero baryon densities. In contrast, the phase with chiral symmetry breaking may exist only at rather large values of $L$.

hep-ph↗
arXiv2010

Chiral density waves in quark matter within the Nambu--Jona-Lasinio model in an external magnetic field

A possibility of formation of static dual scalar and pseudoscalar density wave condensates in dense quark matter is considered for the Nambu--Jona-Lasinio model in an external magnetic field. Within a mean-field approximation, the effective potential of the theory is obtained and its minima are numerically studied; a phase diagram of the system is constructed. It is shown that the presence of a magnetic field favors the formation of spatially inhomogeneous condensate configurations at low temperatures and arbitrary non-zero values of the chemical potential.

hep-ph↗
arXiv2010

Cooper pairing and finite-size effects in a NJL-type four-fermion model

Starting from a NJL-type model with N fermion species fermion and difermion condensates and their associated phase structures are considered at nonzero chemical potential $μ$ and zero temperature in spaces with nontrivial topology of the form $S^1\otimes S^1\otimes S^1$ and $R^2\otimes S^1$. Special attention is devoted to the generation of the superconducting phase. In particular, for the cases of antiperiodic and periodic boundary conditions we have found that the critical curve of the phase transitions between the chiral symmetry breaking and superconducting phases as well as the corresponding condensates and particle densities strongly oscillate vs $λ\sim 1/L$, where $L$ is the length of the circumference $S^1$. Moreover, it is shown that at some finite values of $L$ the superconducting phase transition is shifted to smaller values both of $μ$ and particle density in comparison with the case of $L=\infty$.

hep-ph↗
arXiv2009

Pion condensation in the Gross-Neveu model with nonzero baryon and isospin chemical potentials

The properties of the two-flavored Gross-Neveu model in the (1+1)-dimensional spacetime are investigated in the presence of the isospin $μ_I$ as well as quark number $μ$ chemical potentials both at zero and nonzero temperatures. The consideration is performed in the limit $N_c\to\infty$, i.e. in the case with an infinite number of colored quarks. In the plane of parameters $μ_I,μ$ a rather rich phase structure is found, which contains phases with and without pion condensation. Moreover, we have found a great variety of one-quark excitations of these phases, including gapless and gapped quasiparticles.

hep-ph↗
arXiv2008

Mesons and diquarks in the CFL phase of dense quark matter

The spectrum of meson and diquark excitations of the color--flavor locked (CFL) phase of dense quark matter is considered in the framework of the Nambu -- Jona-Lasinio model. We have found that in this phase all Nambu--Goldstone bosons are realized as scalar and pseudoscalar diquarks. Other diquark excitations are resonances with mass value around 230 MeV. Mesons are stable particles in the CFL phase. Their masses vs chemical potential lie in the interval 300$÷$500 MeV.

hep-ph↗
arXiv2008

Finite size effects in the Gross-Neveu model with isospin chemical potential

The properties of the two-flavored Gross-Neveu model in the (1+1)-dimensional $R^1\times S^1$ spacetime with compactified space coordinate are investigated in the presence of the isospin chemical potential $μ_I$. The consideration is performed in the limit $N_c\to\infty$, i.e. in the case with infinite number of colored quarks. It is shown that at $L=\infty$ ($L$ is the length of the circumference $S^1$) the pion condensation phase is realized for arbitrary small nonzero $μ_I$. At finite values of $L$, the phase portraits of the model in terms of parameters $ν\simμ_I$ and $λ\sim 1/L$ are obtained both for periodic and antiperiodic boundary conditions of the quark field. It turns out that in the plane $(λ,ν)$ there is a strip $0\leλ<λ_c$ which lies as a whole inside the pion condensed phase. In this phase the pion condensation gap is an oscillating function vs both $λ$ (at fixed $ν$) and $ν$ (at fixed $λ$).

hep-ph↗
arXiv2008

Pion condensation of quark matter in the static Einstein universe

In the framework of an extended Nambu--Jona-Lasinio model we are studying pion condensation in quark matter with an asymmetric isospin composition in a gravitational field of the static Einstein universe at finite temperature and chemical potential. This particular choice of the gravitational field configuration enables us to investigate phase transitions of the system with exact consideration of the role of this field in the formation of quark and pion condensates and to point out its influence on the phase portraits. We demonstrate the effect of oscillations of the thermodynamic quantities as functions of the curvature and also refer to a certain similarity between the behavior of these quantities as functions of curvature and finite temperature. Finally, the role of quantum fluctuations for spontaneous symmetry breaking in the case of a finite volume of the universe is shortly discussed.

hep-ph↗
arXiv2007

Mass spectrum of diquarks and mesons in the color--flavor locked phase of dense quark matter

The spectrum of meson and diquark excitations of dense quark matter is considered in the framework of the Nambu -- Jona-Lasinio model with three types of massless quarks in the presense of a quark number chemical potential $μ$. We investigate the effective action of meson- and diquark fields both at sufficiently large values of $μ>μ_c\approx 330$ MeV, where the color--flavor locked (CFL) phase is realized, and in the chirally broken phase of quark matter ($μ<μ_c$). In the last case all nine pseudoscalar mesons are Nambu -- Goldstone (NG) bosons, whereas the mass of the scalar meson nonet is twice the dynamical quark mass. In the chirally broken phase the pseudoscalar diquarks are not allowed to exist as stable particles, but the scalar diquarks might be stable only at a rather strong interaction in the diquark channel. In the case of the CFL phase, all NG bosons of the model are realized as scalar and pseudoscalar diquarks. Moreover, it turns out that massive diquark excitations are unstable for this phase. In particular, for the scalar and pseudoscalar octets of diquark resonances a mass value around 230 MeV was found numerically. In contrast, mesons are stable particles in the CFL phase. Their masses lie in the interval 400$÷$500 MeV for not too large values of $μ>μ_c$.

hep-ph↗
arXiv2007

Diquarks in the color--flavor locked phase of dense quark matter

Diquark excitations of dense quark matter are considered in the framework of the Nambu -- Jona-Lasinio model with three types of massless quarks in the presense of a quark number chemical potential $μ$. We investigate the effective action of meson- and diquark fields at sufficiently high values of $μ$, where the color--flavor locked (CFL) phase is realized, and prove the existence of NG-bosons in the sector of pseudoscalar diquarks. In the sector of scalar diquarks an additional NG-boson is found, corresponding to the spontaneous breaking of the U(1)$_B$ baryon symmetry in the CFL phase. Finally, the existence of massive scalar and pseudoscalar diquark excitations is demonstrated.

hep-ph↗
arXiv2006

Mesons and diquarks in neutral color superconducting quark matter with $β$-equilibrium

The spectrum of meson and diquark excitations in cold color-superconducting (2SC) quark matter is investigated under local color and electric neutrality constraints with $β$-equilibrium. A 2-flavored Nambu--Jona-Lasinio type model including a baryon $μ_B$, color $μ_8$, and electric $μ_Q$ chemical potentials is used. Two relations between coupling constants $H$ and $G$ in the diquark- and quark-antiquark channels, correspondingly, are treated, $H=3G/4$ and $H=G$. At $H=3G/4$ the gapless- and at $H=G$ the gapped neutral color superconductivity is realized. It is shown that color and electrical neutrality together with $β$-equilibrium lead to a strong mass splitting within the pion isotriplet in the 2SC phase (both gapped and gapless), in contrast with non--neutral matter. It is also shown that the properties of the physical $SU(2)_c$-singlet diquark excitation in the 2SC ground state varies for different parameterization schemes. Thus, for $H=3G/4$ one finds a heavy resonance with mass $\sim$ 1100 MeV in the non--neutral (gapped) case, whereas, if neutrality is imposed, a stable diquark with mass $\simμ_Q\sim$ 200 MeV appears in the gapless 2SC phase. For $H=G$, there is again a resonance (with the mass $\sim$ 300 MeV) in the neutral gapped 2SC phase. Hence, the existence of the stable massive SU(2)$_c$-singlet diquark excitation is a new peculiarity of the gapless 2SC.

hep-ph↗
arXiv2006

Quark and pion condensation in a chromomagnetic background field

The general features of quark and pion condensation in dense quark matter with flavor asymmetry have been considered at finite temperature in the presence of a chromomagnetic background field modelling the gluon condensate. In particular, pion condensation in the case of a constant abelian chromomagnetic field and zero temperature has been studied both analytically and numerically. Under the influence of the chromomagnetic background field the effective potential of the system is found to have a global minimum for a finite pion condensate even for small values of the effective quark coupling constant. In the strong field limit, an effective dimensional reduction has been found to take place.

hep-ph↗
arXiv2006

Pion condensation in electrically neutral cold matter with finite baryon density

The possibility of the pion condensation phenomenon in cold and electrically neutral dense baryonic matter is investigated in $β$-equilibrium. For simplicity, the consideration is performed in the framework of a NJL model with two quark flavors at zero current quark mass and for rather small values of the baryon chemical potential, where the diquark condensation might be ignored. Two sets of model parameters are used. For the first one, the pion condensed phase with finite baryon density is realized. In this phase both electrons and the pion condensate take part in the neutralization of the quark electric charge. For the second set of model parameters, the pion condensation is impossible if the neutrality condition is imposed. The behaviour of meson masses vs quark chemical potential has been studied in electrically neutral matter.

hep-ph↗
arXiv2006

Pion condensation in quark matter with finite baryon density

The phase structure of the Nambu -- Jona-Lasinio model at zero temperature and in the presence of baryon- and isospin chemical potentials is investigated. It is shown that in the chiral limit and for a wide range of model parameters there exist two different phases with pion condensation. In the first, ordinary phase, quarks are gapped particles. In the second, gapless pion condensation phase, there is no energy cost for creating only $u$- or both $u$ and $d$ quarks, and the density of baryons is nonzero.

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