arXiv subjects
Publications and source records attributed to Igor A. Shovkovy.
A brief introduction into the properties of dense quark matter is given. Recently proposed gapless color superconducting phases of neutral and beta-equilibrated dense quark matter are discussed. The current status in the field is described, and the promising directions of the future research are outlined.
We propose a new neutrino propulsion mechanism for neutron stars which can lead to strong velocity kicks, needed to explain the observed bimodal velocity distribution of pulsars. The spatial asymmetry in the neutrino emission is naturally provided by a stellar core containing spin-1 color-superconducting quark matter in the A phase. The neutrino propulsion mechanism switches on when the stellar core temperature drops below the transition temperature of this phase.
By referring to the underlying physics behind the color charge neutrality condition in quark matter, we discuss how this condition should be properly imposed in NJL-type models in a phenomenologically meaningful way. In particular, we show that the standard assumption regarding the use of two color chemical potentials, chosen in a very special way, is not justified in general. When used uncritically, such an approach leads to wrong or unphysical conclusions.
We discuss gapless color superconductivity for neutral quark matter in beta equilibrium at zero as well as at nonzero temperature. Basic properties of gapless superconductors are reviewed. The current progress and the remaining problems in the understanding of the phase diagram of strange quark matter are discussed.
The Debye and Meissner screening masses of the gluons and the photon in neutral and beta-equilibrated dense two-flavor quark matter are calculated. The results are presented in a general form that can be used in gapped as well as gapless color superconducting phases. The results for the magnetic screening masses indicate that the system develops a chromomagnetic instability. Possible consequences of the instability are discussed.
The first lecture provides an introduction to the physics of color superconductivity in cold dense quark matter. The main color superconducting phases are briefly described and their properties are listed. The second lecture covers recent developments in studies of color superconducting phases in neutral and beta-equilibrated matter. The properties of gapless color superconducting phases are discussed.
Recent results on the gapless 2SC phase are reviewed. These include: the thermal stability under the constraint of the local charge neutrality condition, the properties at zero and nonzero temperatures, and the color screening properties.
The results for the Debye and Meissner screening masses of the gluons and the photon in the case of neutral and beta-equilibrated dense two-flavor quark matter are presented. In the limits of the normal phase and the ideal two-flavor color superconducting phase, the screening masses coincide with the known results. Most interestingly, we find that the Meissner screening masses squared can be negative, indicating a plasma-type chromomagnetic instability in dense quark matter.
We study the phase diagram of dense, locally neutral three-flavor quark matter as a function of the strange quark mass, the quark chemical potential, and the temperature, employing a general nine-parameter ansatz for the gap matrix. At zero temperature and small values of the strange quark mass, the ground state of matter corresponds to the color-flavor-locked (CFL) phase. At some critical value of the strange quark mass, this is replaced by the recently proposed gapless CFL (gCFL) phase. We also find several other phases, for instance, a metallic CFL (mCFL) phase, a so-called uSC phase where all colors of up quarks are paired, as well as the standard two-flavor color-superconducting (2SC) phase and the gapless 2SC (g2SC) phase.
The contribution of thermally excited electron-positron pairs to the bulk properties of the color-flavor locked quark phase inside compact stars is examined. The presence of these pairs causes the photon mean free path to be much smaller than a typical core radius ($R_0 \simeq 1$ km) for all temperatures above 25 keV so that the photon contribution to the thermal conductivity is much smaller than that of the Nambu-Goldstone bosons. We also find that the electrons and positrons dominate the electrical conductivity, while their contributions to the total thermal energy is negligible.
The cooling mechanism of compact stars with quark cores in the color-flavor locked phase is discussed. It is argued that the high thermal conductivity of the quark core plays a key role in the stellar cooling. It implies that the cooling time of compact stars with color-flavor locked quark cores is similar to that of ordinary neutron stars, unless the star is almost completely made of color-flavor locked quark matter.
In a two-flavor color superconductor, the SU(3)_c gauge symmetry is spontaneously broken by diquark condensation. The Nambu-Goldstone excitations of the diquark condensate mix with the gluons associated with the broken generators of the original gauge group. It is shown how one can decouple these modes with a particular choice of 't Hooft gauge. We then explicitly compute the spectral density for transverse and longitudinal gluons of adjoint color 8. The Nambu-Goldstone excitations give rise to a singularity in the real part of the longitudinal gluon self-energy. This leads to a vanishing gluon spectral density for energies and momenta located on the dispersion branch of the Nambu-Goldstone excitations.
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 breaking of baryon number 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.
The properties of plasmons, Nambu-Goldstone bosons and gapless Carlson-Goldman collective modes in color-flavor locked phase of color superconducting dense quark matter at finite temperature are reviewed. A possibility of a kaon condensation with an abnormal number of the NG bosons is also discussed.
The one-loop effective action in QED at zero and finite temperature is obtained by using the worldline approach. The Feynman rules for the perturbative expansion of the action in the number of derivatives are derived. The general structure of the temperature dependent part of the effective action in an arbitrary external inhomogeneous magnetic field is established. The two-derivative term in the effective action for spinor and scalar QED in a static magnetic background at $T\neq 0$ is calculated.
The one-loop finite temperature effective potential of QED in an external electromagnetic field is obtained using the worldline method. The general structure of the temperature dependent part of the effective action in an arbitrary external inhomogeneous magnetic field is established. The two-derivative effective action of spinor and scalar QED in a static magnetic background at $T\neq 0$ is derived.
The catalysis of chiral symmetry breaking in the massless weakly coupled QED in a magnetic field is studied. It is shown that the effect is due to the dimensional reduction $D\to D-2$ in the dynamics of fermion pairing in a magnetic field. The dynamical mass of fermions (energy gap in the fermion spectrum) is determined. The temperature of the symmetry restoration is estimated analytically.
The mass generation in the (3+1)-dimensional supersymmetric Nambu-Jona-Lasinio model in a constant magnetic field is studied. It is shown that the external magnetic field catalyzes chiral symmetry breaking.