23 research outputs found
Phases of a bilayer Fermi gas
We investigate a two-species Fermi gas in which one species is confined in
two parallel layers and interacts with the other species in the
three-dimensional space by a tunable short-range interaction. Based on the
controlled weak coupling analysis and the exact three-body calculation, we show
that the system has a rich phase diagram in the plane of the effective
scattering length and the layer separation. Resulting phases include an
interlayer s-wave pairing, an intralayer p-wave pairing, a dimer Bose-Einstein
condensation, and a Fermi gas of stable Efimov-like trimers. Our system
provides a widely applicable scheme to induce long-range interlayer
correlations in ultracold atoms.Comment: 5 pages, 5 figures; (v2) stability of trimer is emphasized; (v3)
published versio
CP-violating theta parameter in the domain model of the QCD vacuum
A non-zero CP-violating parameter is treated in the domain model
which assumes a cluster-like vacuum structure whose units are characterised in
particular by a topological charge which is not necessarily an integer number.
In the present paper we restrict consideration to rational values of the
charge. The model has previously been shown to manifest confinement,
spontaneous chiral symmetry breaking and the absence of an axial U(1) Goldstone
boson. We find that the specific structure of the minima of the free energy
density of the domain ensemble forces a -periodicity of observables in
for any number of light quarks, that vacuum doubling occurs at
for any and any value of topological charge . These
features are in agreement with expectations based on anomalous Ward identities
and large effective theories. We find also additional values of
depending on for which vacuum doubling occurs.Comment: 10 pages, 6 figures. Final version with modification of Eq.(2),
additional references, minor typographical correction
Poincar\'e recurrence theorem and the strong CP-problem
The existence in the physical QCD vacuum of nonzero gluon condensates, such
as , requires dominance of gluon fields with finite mean action
density. This naturally allows any real number value for the unit ``topological
charge'' characterising the fields approximating the gluon configurations
which should dominate the QCD partition function. If is an irrational
number then the critical values of the parameter for which CP is
spontaneously broken are dense in , which provides for a mechanism
of resolving the strong CP problem simultaneously with a correct implementation
of symmetry. We present an explicit realisation of this
mechanism within a QCD motivated domain model. Some model independent arguments
are given that suggest the relevance of this mechanism also to genuine QCD.Comment: 8 pages, RevTeX, 3 figures. Revised after referee suggestions. Now
includes model independent argument
Spectral density in resonance region and analytic confinement
We study the role of finite widths of resonances in a nonlocal version of the
Wick-Cutkosky model. The spectrum of bound states is known analytically in this
model and forms linear Regge tragectories. We compute the widths of resonances,
calculate the spectral density in an extension of the Breit-Wigner {\it ansatz}
and discuss a mechanism for the damping of unphysical exponential growth of
observables at high energy due to finite widths of resonances.Comment: 13 pages, RevTeX, 6 figures. Revised version with typographical
corrections and additional comments in conclusion
Impact of the strong electromagnetic field on the QCD effective potential for homogeneous Abelian gluon field configurations
The one-loop quark contribution to the QCD effective potential for the
homogeneous Abelian gluon field in the presence of external strong
electromagnetic field is evaluated. The structure of extrema of the potential
as a function of the angles between chromoelectric, chromomagnetic and
electromagnetic fields is analyzed. In this setup, the electromagnetic field is
considered as an external one while the gluon field represents domain
structured nonperturbative gluon configurations related to the QCD vacuum in
the confinement phase. Two particularly interesting gluon configurations,
(anti-)self-dual and crossed orthogonal chromomagnetic and chromoelectric
fields, are discussed specifically. Within this simplified framework it is
shown that the strong electromagnetic fields can play a catalysing role for a
deconfinement transition. At the qualitative level, the present consideration
can be seen as a highly simplified study of an impact of the electromagnetic
fields generated in relativistic heavy ion collisions on the strongly
interacting hadronic matter.Comment: 9 pages, 4 figure
On the chirality of quark modes
A model for the QCD vacuum based on a domainlike structured background gluon
field with definite duality attributed to the domains has been shown elsewhere
to give confinement of static quarks, a reasonable value for the topological
susceptibility and indications that chiral symmetry is spontaneously broken. In
this paper we study in detail the eigenvalue problem for the Dirac operator in
such a gluon mean field. A study of the local chirality parameter shows that
the lowest nonzero eigenmodes possess a definite mean chirality correlated with
the duality of a given domain. A probability distribution of the local
chirality qualitatively reproduces histograms seen in lattice simulations.Comment: RevTeX4, 5 figures, 14 page
Confinement and Chiral Symmetry Breaking via Domain-Like Structures in the QCD Vacuum
A qualitative mechanism for the emergence of domain structured background
gluon fields due to singularities in gauge field configurations is considered,
and a model displaying a type of mean field approximation to the QCD partition
function based on this mechanism is formulated. Estimation of the vacuum
parameters (gluon condensate, topological susceptibility, string constant and
quark condensate) indicates that domain-like structures lead to an area law for
the Wilson loop, nonzero topological susceptibility and spontaneous breakdown
of chiral symmetry. Gluon and ghost propagators in the presence of domains are
calculated explicitly and their analytical properties are discussed. The
Fourier transforms of the propagators are entire functions and thus describe
confined dynamical fields.Comment: RevTeX, 48 pages (32 pages + Appendices A-E), new references added
[1,2,4,5] and minor formulae corrected for typographical error