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I. A. Shovkovy

Publications and source records attributed to I. A. Shovkovy.

At least 73 records · Page 4Linked to original sources
arXiv2004

Surprises in nonperturbative dynamics in sigma-model at finite density

The linear $SU(2)_L \times SU(2)_R$ sigma-model occupies a unique place in elementary particle physics and quantum field theory. It has been recently realized that when a chemical potential for hypercharge is added, it becomes a toy model for the description of the dynamics of the kaon condensate in high density QCD. We review recent results in nonperturbative dynamics obtained in the ungauged and gauged versions of this model.

hep-ph↗
arXiv2003

Spontaneous rotational symmetry breaking and roton like excitations in gauged sigma-model at finite density

The linear $σ$-model with a chemical potential for hypercharge is a toy model for the description of the dynamics of the kaon condensate in high density QCD. We analyze the dynamics of the gauged version of this model. It is shown that spontaneous breakdown of $SU(2) \times U(1)_{Y}$ symmetry, caused by the chemical potential, is always accompanied by spontaneous breakdown of both rotational symmetry and electromagnetic $U(1)_{em}$. The spectrum of excitations in this model is rich and, because of rotational symmetry breakdown, anisotropic. It is shown that there exist excitation branches that behave as phonon like quasiparticles for small momenta and as roton like ones for large momenta. This suggests that this model can be relevant for anisotropic superfluid systems.

hep-ph↗
arXiv2003

Large N dynamics in QED in a magnetic field

The expression for the dynamical mass of fermions in QED in a magnetic field is obtained for a large number of the fermion flavor N in the framework of 1/N expansion. The existence of a threshold value N_{thr}, dividing the theories with essentially different dynamics, is established. For the number of flavors N << N_{thr}, the dynamical mass is very sensitive to the value of the coupling constant α_b, related to the magnetic scale μ= |eB|. For N of order N_{thr} or larger, a dynamics similar to that in the Nambu-Jona-Lasinio model with cutoff of order |eB| and the dimensional coupling constant G \sim 1/(N|eB|) takes place. In this case, the value of the dynamical mass is essentially α_b independent (the dynamics with an infrared stable fixed point). The value of N_{thr} separates a weak coupling dynamics (with \tildeα_b \equiv Nα_b << 1) from a strong coupling one (with \tildeα_b \gtrsim 1) and is of order 1/α_b.

hep-ph↗
arXiv2003

Fractal structure of the effective action in (quasi-) planar models with long-range interactions

We derive the effective potential for composite fields in a class of (quasi-) planar models with long-range interactions. This class of models can be relevant for high temperature superconductors and graphite. The fractal structure of the effective potential is revealed and its physical interpretation is presented. It is argued that the multi-branched fractal structure of the potential reflects the presence of an infinite tower of excitonic bound states that occur as a result of the long-range interactions.

cond-mat.str-el↗
arXiv2002

Magnetic field driven metal-insulator phase transition in planar systems

A theory of the magnetic field driven (semi-)metal-insulator phase transition is developed for planar systems with a low density of carriers and a linear (i.e., relativistic like) dispersion relation for low energy quasiparticles. The general structure of the phase diagram of the theory with respect to the coupling constant, the chemical potential and temperature is derived in two cases, with and without an external magnetic field. The conductivity and resistivity as functions of temperature and magnetic field are studied in detail. An exact relation for the value of the "offset" magnetic field $B_c$, determining the threshold for the realization of the phase transition at zero temperature, is established. The theory is applied to the description of a recently observed phase transition induced by a magnetic field in highly oriented pyrolytic graphite.

cond-mat↗
arXiv2002

Quark color superconductivity and the cooling of compact stars

The thermal conductivity of the color-flavor locked phase of dense quark matter is calculated. The dominant contribution to the conductivity comes from photons and Nambu-Goldstone bosons associated with the breaking of baryon number, both of which are trapped in the quark core. Because of their very large mean free path the conductivity is also very large. The cooling of the quark core arises mostly from the heat flux across the surface of direct contact with the nuclear matter. As the thermal conductivity of the neighboring layer is also high, the whole interior of the star should be nearly isothermal. Our results imply that the cooling time of compact stars with color-flavor locked quark cores is similar to that of ordinary neutron stars.

astro-ph↗
arXiv2002

Magnetic catalysis and anisotropic confinement in QCD

The expressions for dynamical masses of quarks in the chiral limit in QCD in a strong magnetic field are obtained. A low energy effective action for the corresponding Nambu-Goldstone bosons is derived and the values of their decay constants as well as the velocities are calculated. The existence of a threshold value of the number of colors $N^{thr}_c$, dividing the theories with essentially different dynamics, is established. For the number of colors $N_c \ll N^{thr}_c$, an anisotropic dynamics of confinement with the confinement scale much less than $Λ_{QCD}$ and a rich spectrum of light glueballs is realized. For $N_c$ of order $N^{thr}_c$ or larger, a conventional confinement dynamics takes place. It is found that the threshold value $N^{thr}_c$ grows rapidly with the magnetic field [$N^{thr}_c \gtrsim 100$ for $|eB| \gtrsim (1{GeV})^2$]. In contrast to QCD with a nonzero baryon density, there are no principal obstacles for checking these results and predictions in lattice computer simulations.

hep-ph↗
arXiv2002

Spontaneous Symmetry Breaking with Abnormal Number of Nambu-Goldstone Bosons and Kaon Condensate

We describe a class of relativistic models incorporating finite density of matter in which spontaneous breakdown of continuous symmetries leads to a lesser number of Nambu-Goldstone bosons than that required by the Goldstone theorem. This class, in particular, describes the dynamics of the kaon condensate in the color-flavor locked phase of high density QCD. We describe the spectrum of low energy excitations in this dynamics and show that, despite the presence of a condensate and gapless excitations, this system is not a superfluid.

hep-ph↗
arXiv2001

Diquark composites in the color superconducting phase of two flavor dense QCD

We study the Bethe-Salpeter equations for spin zero diquark composites in the color superconducting phase of N_f=2 cold dense QCD. The explicit form of the spectrum of the diquarks, containing an infinite tower of narrow (at high density) resonances, is derived. It is argued that there are five pseudo-Nambu-Goldstone bosons (pseudoscalars) that remain almost massless at large chemical potential. These five pseudoscalars, along with the massless quarks of the third color should play an important role in the infrared dynamics of N_f=2 dense QCD.

hep-ph↗
arXiv2001

Collective modes of color-flavor locked phase of dense QCD at finite temperature

A detailed analysis of collective modes that couple to either vector or axial color currents in color-flavor locked phase of color superconducting dense quark matter at finite temperature is presented. Among the realm of collective modes, including the plasmons and the Nambu-Goldstone bosons, we also reveal the gapless Carlson-Goldman modes, resembling the scalar Nambu-Golstone bosons. These latter exist only in a close vicinity of the critical line. Their presence does not eliminate the Meissner effect, proving that the system remains in the color broken phase. The finite temperature properties of the plasmons and the Nambu-Goldstone bosons are also studied. In addition to the ordinary plasmon, we also reveal a "light" plasmon which has a narrow width and whose mass is of the order of the superconducting gap.

hep-ph↗
arXiv2001

Carlson-Goldman modes in the color superconducting phase of dense QCD

We predict the existence of the gapless Carlson-Goldman modes in the color-flavor locked color superconducting phase of dense QCD. These modes resemble Nambu-Goldstone modes of the superconducting phase below the critical temperature where the Anderson-Higgs mechanism takes place. These modes exist in the broken phase in the vicinity of the critical line. Their presence does not eliminate the Meissner effect. The effect of Landau damping on the width of the Carlson-Goldman modes is discussed.

hep-ph↗
arXiv2001

Masses of the pseudo-Nambu-Goldstone bosons in two flavor color superconducting phase

The masses of the pseudo-Nambu-Goldstone bosons in the color superconducting phase of dense QCD with two light flavors are estimated by making use of the Cornwall-Jackiw-Tomboulis effective action. Parametrically, the masses of the doublet and antidoublet bosons are suppressed by a power of the coupling constant as compared to the value of the superconducting gap. This is qualitatively different from the mass expression for the singlet pseudo-Nambu-Goldstone boson, resulting from non-perturbative effects. It is argued that the (anti-) doublet pseudo-Nambu-Goldstone bosons form colorless [with respect to the unbroken SU(2)_{c}] charmonium-like bound states. The corresponding binding energy is also estimated.

hep-ph↗
arXiv2001

Color superconductivity and nondecoupling phenomena in 2+1 dimensional QCD

The possibility of generating a color superconducting state in 2+1 dimensional QCD is analyzed. The gap equation in the leading, hard-dense loop improved, one-gluon exchange approximation is derived and solved. The magnitude of the order parameter is proportional to a power of the coupling constant. For an asymptotically large chemical potential, a qualitatevely new (with respect to the 3+1 dimensional case) phenomenon of nondecoupling of the fermion pairing dynamics from the infrared one is revealed and discussed.

hep-ph↗
arXiv2000

Bethe-Salpeter equation for diquarks in color-flavor locked phase of cold dense QCD

The Bethe-Salpeter equations for diquarks with the quantum numbers of the Nambu-Goldstone bosons are analyzed in the color-flavor locked phase of cold dense QCD with three quark flavors. The decay constants and the velocities of the Nambu-Goldstone bosons are calculated in the Pagels-Stokar approximation. It is also shown that, in contrast to the case of dense QCD with two flavors, there are no massive radial excitations with quantum numbers of the Nambu-Goldstone bosons in the color-flavor locked phase. The role of the Meissner effect in the pairing dynamics of diquarks is explained.

hep-ph↗
arXiv2000

The Spectrum of Diquark Composites in Cold Dense QCD

The Bethe-Salpeter equations for spin zero diquark composites in the color superconducting phase of $N_f=2$ and $N_f=3$ cold dense QCD are studied. The explicit form of the spectrum of the diquarks with the quantum numbers of the (pseudo-) Nambu-Goldstone bosons is derived.

nucl-th↗
arXiv2000

Diquarks in cold dense QCD with two flavors

We derive and analyze the Bethe-Salpeter equations for spin zero diquarks in the color superconducting phase of cold dense QCD with two massless flavors. The spectrum of diquarks contains an infinite number of massive excitations and five (nearly) massless pseudoscalars. The former are singlets while the latter include a doublet, an antidoublet and a singlet with respect to the unbroken $SU(2)_{c}$. Because of an approximate parity doubling at large chemical potential, all massive states come in pairs. The decay constants, as well as the velocities of the (nearly) massless pseudoscalars are derived. The different role of the Meissner effect for tightly bound states and quasiclassical bound states is revealed.

hep-ph↗
arXiv1999

Schwinger-Dyson Approach to Color Superconductivity in Dense QCD

The problem of color superconductivity in dense QCD is reconsidered in the improved rainbow approximation to the Schwinger-Dyson equation. The effect of the unscreened magnetic modes of gluons on the value of the color condensate is studied. In particular, it is shown that, at sufficiently large values of the chemical potential, these modes lead to the enhancement of the superconducting order parameter. The interplay between the instanton induced interaction and the one-gluon induced one in color superconductivity is discussed.

hep-ph↗