995 research outputs found
Light scattering and dissipative dynamics of many fermionic atoms in an optical lattice
We investigate the many-body dissipative dynamics of fermionic atoms in an
optical lattice in the presence of incoherent light scattering. Deriving and
solving a master equation to describe this process microscopically for many
particles, we observe contrasting behaviour in terms of the robustness against
this type of heating for different many-body states. In particular, we find
that the magnetic correlations exhibited by a two-component gas in the Mott
insulating phase should be particularly robust against decoherence from light
scattering, because the decoherence in the lowest band is suppressed by a
larger factor than the timescales for effective superexchange interactions that
drive coherent dynamics. Furthermore, the derived formalism naturally
generalizes to analogous states with SU(N) symmetry. In contrast, for typical
atomic and laser parameters, two-particle correlation functions describing
bound dimers for strong attractive interactions exhibit superradiant effects
due to the indistinguishability of off-resonant photons scattered by atoms in
different internal states. This leads to rapid decay of correlations describing
off-diagonal long-range order for these states. Our predictions should be
directly measurable in ongoing experiments, providing a basis for
characterising and controlling heating processes in quantum simulation with
fermions.Comment: 18 pages, 7 figure
Effects of Velocity-Dependent Dark Matter Annihilation on the Energy Spectrum of the Extragalactic Gamma-ray Background
We calculate the effects of velocity-dependent dark matter annihilation cross
sections on the intensity of the extragalactic gamma-ray background. Our
formalism does not assume a locally thermal distribution of dark matter
particles in phase space, and is valid for arbitrary velocity-dependent
annihilation. As concrete examples, we calculate the effects of p-wave
annihilation (with the -weighted cross section of ) on the
mean intensity of extragalactic gamma rays produced in cosmological dark matter
halos. This velocity variation makes the shape of the energy spectrum harder,
but this change in the shape is too small to see unless b/a\agt 10^6. While
we find no such models in the parameter space of the Minimal Supersymmetric
Standard Model (MSSM), we show that it is possible to find b/a\agt 10^6 in
the extension MSSM. However, we find that the most dominant
effect of the p-wave annihilation is the suppression of the amplitude of the
gamma-ray background. A non-zero at the dark matter freeze-out epoch
requires a smaller value of in order for the relic density constraint to be
satisfied, suppressing the amplitude by a factor as low as for a
thermal relic. Non-thermal relics will have weaker amplitude suppression. As
another velocity-dependent effect, we calculate the spectrum for s-wave
annihilation into fermions enhanced by the attractive Sommerfeld effect.
Resonances associated with this effect result in significantly enhanced
intensities, with a slightly softer energy spectrum.Comment: 18 pages, 10 figure
Lattice Monte Carlo Simulations with Two Impurity Worldlines
We develop the impurity lattice Monte Carlo formalism, for the case of two
distinguishable impurities in a bath of polarized fermions. The majority
particles are treated as explicit degrees of freedom, while the impurities are
described by worldlines. The latter serve as localized auxiliary fields, which
affect the majority particles. We apply the method to non-relativistic
three-dimensional systems of two impurities and a number of majority particles
where both the impurity-impurity interaction and the impurity-majority
interaction have zero range. We consider the case of an attractive
impurity-majority interaction, and we study the formation and disintegration of
bound states as a function of the impurity-impurity interaction strength. We
also discuss the potential applications of this formalism to other quantum
many-body systems.Comment: 7 pages, 4 figure
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