20,871 research outputs found
Directional `superradiant' collisions: bosonic amplification of atom pairs emitted from an elongated Bose-Einstein condensate
We study spontaneous directionality in the bosonic amplification of atom
pairs emitted from an elongated Bose-Einstein condensate (BEC), an effect
analogous to `superradiant' emission of atom-photon pairs. Using a simplified
model, we make analytic predictions regarding directional effects for both
atom-atom and atom-photon emission. These are confirmed by numerical mean-field
simulations, demonstrating the the feasibility of nearly perfect directional
emission along the condensate axis. The dependence of the emission angle on the
pump strength for atom-atom pairs is significantly different than for
atom-photon pairs
Electroweak Baryogenesis with dimension-6 Higgs interactions
We present the computation of the baryon asymmetry in the SM amplified by
dimension-6 Higgs interactions using the WKB approximation. Analyzing the
one-loop potential it turns out that the phase transition is strongly first
order in a wide range of the parameters. It is ensured not to wash out the net
baryon number gained previously even for Higgs masses up to at least 170 GeV.
In addition dimension-6 operators induce new sources of CP violation. Novel
source terms which enhance the generated baryon asymmetry emerge in the
transport equations. This model predicts a baryon to entropy ratio close to the
observed value for a large part of the parameter space.Comment: 10 pages, 4 figures, Talk given at the 8th International Moscow
School of Physic
A note on the convergence of parametrised non-resonant invariant manifolds
Truncated Taylor series representations of invariant manifolds are abundant
in numerical computations. We present an aposteriori method to compute the
convergence radii and error estimates of analytic parametrisations of
non-resonant local invariant manifolds of a saddle of an analytic vector field,
from such a truncated series. This enables us to obtain local enclosures, as
well as existence results, for the invariant manifolds
Critical points in edge tunneling between generic FQH states
A general description of weak and strong tunneling fixed points is developed
in the chiral-Luttinger-liquid model of quantum Hall edge states. Tunneling
fixed points are a subset of `termination' fixed points, which describe
boundary conditions on a multicomponent edge. The requirement of unitary time
evolution at the boundary gives a nontrivial consistency condition for possible
low-energy boundary conditions. The effect of interactions and random hopping
on fixed points is studied through a perturbative RG approach which generalizes
the Giamarchi-Schulz RG for disordered Luttinger liquids to broken left-right
symmetry and multiple modes. The allowed termination points of a multicomponent
edge are classified by a B-matrix with rational matrix elements. We apply our
approach to a number of examples, such as tunneling between a quantum Hall edge
and a superconductor and tunneling between two quantum Hall edges in the
presence of interactions. Interactions are shown to induce a continuous
renormalization of effective tunneling charge for the integrable case of
tunneling between two Laughlin states. The correlation functions of
electronlike operators across a junction are found from the B matrix using a
simple image-charge description, along with the induced lattice of boundary
operators. Many of the results obtained are also relevant to ordinary Luttinger
liquids.Comment: 23 pages, 6 figures. Xiao-Gang Wen: http://dao.mit.edu/~we
Continuous topological phase transitions between clean quantum Hall states
Continuous transitions between states with the {\em same} symmetry but
different topological orders are studied. Clean quantum Hall (QH) liquids with
neutral quasiparticles are shown to have such transitions. For clean bilayer
(nnm) states, a continous transition to other QH states (including non-Abelian
states) can be driven by increasing interlayer repulsion/tunneling. The
effective theories describing the critical points at some transitions are
derived.Comment: 4 pages, RevTeX, 2 eps figure
The Baryon asymmetry in the Standard Model with a low cut-off
We study the generation of the baryon asymmetry in a variant of the standard
model, where the Higgs field is stabilized by a dimension-six interaction.
Analyzing the one-loop potential, we find a strong first order electroweak
phase transition for Higgs masses up to at least 170 GeV. Dimension-six
operators induce also new sources of CP violation. We compute the baryon
asymmetry in the WKB approximation. Novel source terms in the transport
equations enhance the generated baryon asymmetry. For a wide range of
parameters the model predicts a baryon asymmetry close to the observed value.Comment: 22 pages, latex, 6 figure
Properties of Galaxy Groups in the SDSS: II.- AGN Feedback and Star Formation Truncation
Successfully reproducing the galaxy luminosity function and the bimodality in
the galaxy distribution requires a mechanism that can truncate star formation
in massive haloes. Current models of galaxy formation consider two such
truncation mechanisms: strangulation, which acts on satellite galaxies, and AGN
feedback, which predominantly affects central galaxies. The efficiencies of
these processes set the blue fraction of galaxies as function of galaxy
luminosity and halo mass. In this paper we use a galaxy group catalogue
extracted from the Sloan Digital Sky Survey (SDSS) to determine these
fractions. To demonstrate the potential power of this data as a benchmark for
galaxy formation models, we compare the results to the semi-analytical model
for galaxy formation of Croton et al. (2006). Although this model accurately
fits the global statistics of the galaxy population, as well as the shape of
the conditional luminosity function, there are significant discrepancies when
the blue fraction of galaxies as a function of mass and luminosity is compared
between the observations and the model. In particular, the model predicts (i)
too many faint satellite galaxies in massive haloes, (ii) a blue fraction of
satellites that is much too low, and (iii) a blue fraction of centrals that is
too high and with an inverted luminosity dependence. In the same order, we
argue that these discrepancies owe to (i) the neglect of tidal stripping in the
semi-analytical model, (ii) the oversimplified treatment of strangulation, and
(iii) improper modeling of dust extinction and/or AGN feedback. The data
presented here will prove useful to test and calibrate future models of galaxy
formation and in particular to discriminate between various models for AGN
feedback and other star formation truncation mechanisms.Comment: 16 pages, 5 figures, submitted to MNRA
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