888 research outputs found

### High Density Effective Theory Confronts the Fermi Liquid

The high density effective theory recently introduced by Hong and Hsu to
describe ultradense relativistic fermionic matter is used to calculate the
tree-level forward scattering amplitude between two particles at the Fermi
surface. While the direct term correctly reproduces that of the underlying
gauge theory, the exchange term has the wrong sign. The physical consequences
are discussed in the context of Landau's theoretical description of the Fermi
liquid.Comment: 15 pages, 2 figures; conclusion expanded, reference adde

### How the quark self-energy affects the color-superconducting gap

We consider color superconductivity with two flavors of massless quarks which
form Cooper pairs with total spin zero. We solve the gap equation for the
color-superconducting gap parameter to subleading order in the QCD coupling
constant $g$ at zero temperature. At this order in $g$, there is also a
previously neglected contribution from the real part of the quark self-energy
to the gap equation. Including this contribution leads to a reduction of the
color-superconducting gap parameter \f_0 by a factor b_0'=\exp \big[ -(\p
^2+4)/8 \big]\simeq 0.177. On the other hand, the BCS relation T_c\simeq
0.57\f_0 between \f_0 and the transition temperature $T_c$ is shown to
remain valid after taking into account corrections from the quark self-energy.
The resulting value for $T_c$ confirms a result obtained previously with a
different method.Comment: Revtex, 8 pages, no figur

### Positivity of High Density Effective Theory

We show that the effective field theory of low energy modes in dense QCD has
positive Euclidean path integral measure. The complexity of the measure of QCD
at finite chemical potential can be ascribed to modes which are irrelevant to
the dynamics at sufficiently high density. Rigorous inequalities follow at
asymptotic density. Lattice simulation of dense QCD should be possible using
the quark determinant calculated in the effective theory.Comment: 10 pages, Revised version, to appear in Rapid Communications of
Physical Review

### Holographic Construction of Technicolor Theory

We construct a dual description of technicolor theory based on the D4/D8
brane configuration. A strongly-coupled technicolor theory is identified as the
effective theory on D-branes, and from the gauge/gravity correspondence, we
explore the weakly-coupled holographic description of dynamical electroweak
symmetry breaking. It is found from the D-brane probe action that the masses of
W and Z bosons are given by the decay constant of technipion, and the
technimesons become hierarchically heavy. Moreover, the couplings of heavier
modes to standard model fermions are rather suppressed. The oblique correction
parameters are also evaluated and found to be small except for the S parameter,
which can be reduced by modifying the model. The fermion fields are introduced
at the intersections of D-branes and their masses are generated via massive
gauge bosons from open strings stretching between D-branes.Comment: 23 pages; references added, minor change

### Generalized Ward identity and gauge invariance of the color-superconducting gap

We derive a generalized Ward identity for color-superconducting quark matter
via the functional integral approach. The identity implies the gauge
independence of the color-superconducting gap parameter on the quasi-particle
mass shell to subleading order in covariant gauge.Comment: 5 pages, 1 Postscript figure, uses Revte

### Aspects of the Color Flavor Locking phase of QCD in the Nambu-Jona Lasinio approximation

We study two aspects of the CFL phase of QCD in the NJL approximation. The
first one is the issue of the dependence on \mu of the ultraviolet cutoff in
the gap equation, which is solved allowing a running coupling constant. The
second one is the dependence of the gap on the strange quark mass; using the
high density effective theory we perform an expansion in the parameter
(m_s/\mu)^2 after checking that its numerical validity is very good already at
first order.Comment: LaTeX file, 6 figure

### Longitudinal gluons and Nambu-Goldstone bosons in a two-flavor color superconductor

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.Comment: 16 pages, 4 figures, minor revisions to text, one ref. adde

### A note on fermions in holographic QCD

We study the fermionic sector of a probe D8-brane in the supergravity
background made of D4-branes compactified on a circle with supersymmetry broken
explicitly by the boundary conditions. At low energies the dual field theory is
effectively four-dimensional and has proved surprisingly successful in
recovering qualitative and quantitative properties of QCD. We investigate
fluctuations of the fermionic fields on the probe D8-brane and interpret these
as mesinos (fermionic superpartners of mesons). We demonstrate that the masses
of these modes are comparable to meson masses and show that their interactions
with ordinary mesons are not suppressed.Comment: 21+1 pp, 1 figure; v2: typos corrected, refs. adde

### Scalar-isoscalar excitation in dense quark matter

We study the spectrum of scalar-isoscalar excitations in the color-flavor
locked phase of dense quark matter. The sigma meson in this phase appears as a
four-quark state (of diquark and anti-diquark) with a well-defined mass and
extremely small width, as a consequence of it's small coupling to two pions.
The quark particle/hole degrees of freedom also contribute significantly to the
correlator just above the threshold 2\Delta where \Delta is the superconducting
gap.Comment: RevTeX, 11 pages, 4 fig

### Mass Generation in the Supersymmetric Nambu--Jona--Lasinio Model in an External Magnetic Field

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.Comment: LaTeX file, 6 pages. Talk given at the International Seminar
dedicated to the memory of Dmitrij Volkov "Supersymmetry and Quantum Field
Theory", Kharkov, Ukraine, January 5-7, 199

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