Neutrino Superfluidity

It is shown that Dirac-type neutrinos display BCS superfluidity for any nonzero mass. The Cooper pairs are formed by attractive scalar Higgs boson exchange between left- and right-handed neutrinos; in the standard SU(2)xU(1) theory, right-handed neutrinos do not couple to any other boson. The value of the gap, the critical temperature, and the Pippard coherence length are calculated for arbitrary values of the neutrino mass and chemical potential. Although such a superfluid could conceivably exist, detecting it would be a major challenge.Comment: This is the version published in PR

On the imaginary parts and infrared divergences of two-loop vector boson self-energies in thermal QCD

We calculate the imaginary part of the retarded two-loop self-energy of a static vector boson in a plasma of quarks and gluons of temperature T, using the imaginary time formalism. We recombine various cuts of the self-energy to generate physical processes. We demonstrate how cuts containing loops may be reinterpreted in terms of interference between Order $\alpha$ tree diagrams and the Born term along with spectators from the medium. We apply our results to the rate of dilepton production in the limit of dilepton invariant mass E>>T. We find that all infrared and collinear singularities cancel in the final result obtained in this limit.Comment: references added, typos corrected, slightly abridged, version accepted for publication in Phys. Rev.

Thermal Duality and Hagedorn Transition from p-adic Strings

We develop the finite temperature theory of p-adic string models. We find that the thermal properties of these non-local field theories can be interpreted either as contributions of standard thermal modes with energies proportional to the temperature, or inverse thermal modes with energies proportional to the inverse of the temperature, leading to a "thermal duality" at leading order (genus one) analogous to the well known T-duality of string theory. The p-adic strings also recover the asymptotic limits (high and low temperature) for arbitrary genus that purely stringy calculations have yielded. We also discuss our findings surrounding the nature of the Hagedorn transition.Comment: 4 pages and 4 figure

Energy and momentum relaxation of heavy fermion in dense and warm plasma

We determine the drag and the momentum diffusion coefficients of heavy fermion in dense plasma. It is seen that in degenerate matter drag coefficient at the leading order mediated by transverse photon is proportional to $(E-\mu)^2$ while for the longitudinal exchange this goes as $(E-\mu)^3$. We also calculate the longitudinal diffusion coefficient to obtain the Einstein relation in a relativistic degenerate plasma. Finally, finite temperature corrections are included both for the drag and the diffusion coefficients.Comment: 8 pages, 1 eps figure, typos corrected and paragraphs rearranged. Accepted for publication in Physical Review

Causal amplitudes in the Schwinger model at finite temperature

We show, in the imaginary time formalism, that the temperature dependent parts of all the retarded (advanced) amplitudes vanish in the Schwinger model. We trace this behavior to the CPT invariance of the theory and give a physical interpretation of this result in terms of forward scattering amplitudes of on-shell thermal particles.Comment: 4 pages with 5 figures, two minor typos corrected, to appear in Physical Review

The thermal operator representation for Matsubara sums

We prove in full generality the thermal operator representation for Matsubara sums in a relativistic field theory of scalar and fermionic particles. It states that the full result of performing the Matsubara sum associated to any given Feynman graph, in the imaginary-time formalism of finite-temperature field theory, can be directly obtained from its corresponding zero-temperature energy integral, by means of a simple linear operator, which is independent of the external Euclidean energies and whose form depends solely on the topology of the graph.Comment: 9 pages, 1 figure, RevTe

Color-superconductivity in the strong-coupling regime of Landau gauge QCD

The chirally unbroken and the superconducting 2SC and CFL phases are investigated in the chiral limit within a Dyson-Schwinger approach for the quark propagator in QCD. The hierarchy of Green's functions is truncated such that at vanishing density known results for the vacuum and at asymptotically high densities the corresponding weak-coupling expressions are recovered. The anomalous dimensions of the gap functions are analytically calculated. Based on the quark propagator the phase structure is studied, and results for the gap functions, occupation numbers, coherence lengths and pressure differences are given and compared with the corresponding expressions in the weak-coupling regime. At moderate chemical potentials the quasiparticle pairing gaps are several times larger than the extrapolated weak-coupling results.Comment: 14 pages, 9 figures; v2: one reference adde

Representation of spectral functions and thermodynamics

In this paper we study the question of effective field assignment to measured or nonperturbatively calculated spectral functions. The straightforward procedure is to approximate it by a sum of independent Breit-Wigner resonances, and assign an independent field to each of these resonances. The problem with this idea is that it introduces new conserved quantities in the free model (the new particle numbers), therefore it changes the symmetry of the system. We avoid this inconsistency by representing each quantum channel with a single effective field, no matter how complicated the spectral function is. Thermodynamical characterization of the system will be computed with this representation method, and its relation to the independent resonance approximation will be discussed.Comment: 15 pages, 9 figures, revtex

Photons from axial-vector radiative decay in a hadron gas

Strange and non-strange axial-vector meson radiative decays contribute to photon production in hadron gas. One- and two-hadron radiative decay modes of $b_{1}(1235)$, $a_{1}(1260)$ and $K_{1}(1270)$ are studied. At 200 MeV temperature and for a narrow range in photon energies they contribute more to the net thermal photon production rate than $\pi\rho\rightarrow \pi\gamma$, $\pi\pi\rightarrow \rho\gamma$ or $\rho\rightarrow\pi\pi\gamma$. They provide significant contribution to the rate for photon energies as high as 1.5--2.0 GeV. For higher energies they are less important.Comment: 10 pages + 7 figures uuencoded in separate file, MSUCL-92