26,474 research outputs found
Gradient Catastrophe and Fermi Edge Resonances in Fermi Gas
A smooth spatial disturbance of the Fermi surface in a Fermi gas inevitably
becomes sharp. This phenomenon, called {\it the gradient catastrophe}, causes
the breakdown of a Fermi sea to disconnected parts with multiple Fermi points.
We study how the gradient catastrophe effects probing the Fermi system via a
Fermi edge singularity measurement. We show that the gradient catastrophe
transforms the single-peaked Fermi-edge singularity of the tunneling (or
absorption) spectrum to a set of multiple asymmetric singular resonances. Also
we gave a mathematical formulation of FES as a matrix Riemann-Hilbert problem
Progress in Electroweak Baryogenesis
Recent work on generating the excess of matter over antimatter in the early
universe during the electroweak phase transition is reviewed.Comment: 50 pages (figures on request), uses harvmac (table of contents
correct for "l" format), UCSD-93-2,BU-HEP-93-
Lattice study of trapped fermions at unitarity
We present a lattice study of up to N=20 unitary fermions confined to a
harmonic trap. Our preliminary results show better than 1% agreement with high
precision solutions to the many-body Schrodinger equation for up to N=6. We are
able to make predictions for larger N which were inaccessible by the
Hamiltonian approach due to computational limitations. Harmonic traps are used
experimentally to study cold atoms tuned to a Feshbach resonance. We show that
they also provide certain benefits to numerical studies of many-body
correlators on the lattice. In particular, we anticipate that the methods
described here could be used for studying nuclear physics.Comment: 7 pages, 5 figures, presented at the XXVIII International Symposium
on Lattice Field Theory (Lattice 2010), Villasimius, Italy, June 14-19 201
Lattice calculation for unitary fermions in a finite box
A fundamental constant in systems of unitary fermions is the so-called
Bertsch parameter, the ratio of the ground state energy for spin paired unitary
fermions to that for free fermions at the same density. I discuss how we
computed this parameter as well as the pairing gap using a recently developed
lattice construction for unitary fermions, by measuring correlation functions
for up to 38 fermions in a finite box. Our calculation illustrates interesting
issues facing the study of many-body states on the lattice, which may
eventually be confronted in QCD calculations as well.Comment: 7 pages, 6 figures, The XXVIII International Symposium on Lattice
Field Theory, Lattice2010, June 14-19, 2010, Villasimius, Ital
A lattice theory for low energy fermions at finite chemical potential
We construct a lattice theory describing a system of interacting
nonrelativistic spin s=1/2 fermions at nonzero chemical potential. The theory
is applicable whenever the interparticle separation is large compared to the
range of the two-body potential, and does not suffer from a sign problem. In
particular, the theory could be useful in studying the thermodynamic limit of
fermion systems for which the scattering length is much larger than the
interparticle spacing, with applications to realistic atomic systems and dilute
neutron gases.Comment: Revised introduction, several typos fixed. Conforms to version
accepted for publication in Phys. Rev. Let
Exotic Axions
We show that axion phenomenology may be significantly different than
conventionally assumed in theories which exhibit late phase transitions (below
the QCD scale). In such theories one can find multiple pseudoscalars with
axion-like couplings to matter, including a string scale axion, whose decay
constant far exceeds the conventional cosmological bound. Such theories have
several dark matter candidates.Comment: 5 pages, 1 figure, References adde
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