115 research outputs found
Controlling the Momentum Current of an Off-resonant Ratchet
We experimentally investigate the phenomenon of a quantum ratchet created by
exposing a Bose-Einstein Condensate to short pulses of a potential which is
periodic in both space and time. Such a ratchet is manifested by a directed
current of particles, even though there is an absence of a net bias force. We
confirm a recent theoretical prediction [M. Sadgrove and S. Wimberger, New J.
Phys. \textbf{11}, 083027 (2009)] that the current direction can be controlled
by experimental parameters which leave the underlying symmetries of the system
unchanged. We demonstrate that this behavior can be understood using a single
variable containing many of the experimental parameters and thus the ratchet
current is describable using a single universal scaling law.Comment: arXiv admin note: substantial text overlap with arXiv:1210.565
Dynamical tunneling of a Bose-Einstein condensate in periodically driven systems
We report measurements of dynamical tunneling rates of a Bose-Einstein
condensate across a barrier in classical phase space. The atoms are initially
prepared in quantum states that extend over a classically regular island
region. We focus on the specific system of quantum accelerator modes of the
kicked rotor in the presence of gravity. Our experimental data is supported by
numerical simulations taking into account imperfections mainly from spontaneous
emission. Furthermore, we predict experimentally accessible parameter ranges
over which direct tunneling could be readily observed if spontaneous emission
was further suppressed. Altogether, we provide a proof-of-principle for the
experimental accessibility of dynamical tunneling rates in periodically driven
systems.Comment: Improved versio
Multiple micro-optical atom traps with a spherically aberrated laser beam
We report on the loading of atoms contained in a magneto-optic trap into
multiple optical traps formed within the focused beam of a CO_{2} laser. We
show that under certain circumstances it is possible to create a linear array
of dipole traps with well separated maxima. This is achieved by focusing the
laser beam through lenses uncorrected for spherical aberration. We demonstrate
that the separation between the micro-traps can be varied, a property which may
be useful in experiments which require the creation of entanglement between
atoms in different micro-traps. We suggest other experiments where an array of
these traps could be useful.Comment: 10 pages, 3 figure
Dark matter allowed scenarios for Yukawa-unified SO(10) SUSY GUTs
Simple supersymmetric grand unified models based on the gauge group SO(10)
require --in addition to gauge and matter unification-- the unification of
t-b-\tau Yukawa couplings. Yukawa unification, however, only occurs for very
special values of the soft SUSY breaking parameters. We perform a search using
a Markov Chain Monte Carlo (MCMC) technique to investigate model parameters and
sparticle mass spectra which occur in Yukawa-unified SUSY models, where we also
require the relic density of neutralino dark matter to saturate the
WMAP-measured abundance. We find the spectrum is characterizd by three mass
scales: first/second generation scalars in the multi-TeV range, third
generation scalars in the TeV range, and gauginos in the \sim 100 GeV range.
Most solutions give far too high a relic abundance of neutralino dark matter.
The dark matter discrepancy can be rectified by 1. allowing for neutralino
decay to axino plus photon, 2. imposing gaugino mass non-universality or 3.
imposing generational non-universality. In addition, the MCMC approach finds 4.
a compromise solution where scalar masses are not too heavy, and where
neutralino annihilation occurs via the light Higgs h resonance. By imposing
weak scale Higgs soft term boundary conditions, we are also able to generate 5.
low \mu, m_A solutions with neutralino annihilation via a light A resonance,
though these solutions seem to be excluded by CDF/D0 measurements of the B_s\to
\mu^+\mu^- branching fraction. Based on the dual requirements of Yukawa
coupling unification and dark matter relic density, we predict new physics
signals at the LHC from pair production of 350--450 GeV gluinos. The events are
characterized by very high b-jet multiplicity and a dilepton mass edge around
mz2-mz1 \sim 50-75 GeV.Comment: 35 pages with 21 eps figure
Number phase uncertainty relations: verification by homodyning
It is shown that fundamental uncertainty relations between photon number and
canonical phase of a single-mode optical field can be verified by means of
balanced homodyne measurement. All the relevant quantities can be sampled
directly from the measured phase-dependent quadrature distribution.Comment: 1 Ps figure (divided in 3 subfigures) using REVTE
Gaugino Anomaly Mediated SUSY Breaking: phenomenology and prospects for the LHC
We examine the supersymmetry phenomenology of a novel scenario of
supersymmetry (SUSY) breaking which we call Gaugino Anomaly Mediation, or
inoAMSB. This is suggested by recent work on the phenomenology of flux
compactified type IIB string theory. The essential features of this scenario
are that the gaugino masses are of the anomaly-mediated SUSY breaking (AMSB)
form, while scalar and trilinear soft SUSY breaking terms are highly
suppressed. Renormalization group effects yield an allowable sparticle mass
spectrum, while at the same time avoiding charged LSPs; the latter are common
in models with negligible soft scalar masses, such as no-scale or gaugino
mediation models. Since scalar and trilinear soft terms are highly suppressed,
the SUSY induced flavor and CP-violating processes are also suppressed. The
lightest SUSY particle is the neutral wino, while the heaviest is the gluino.
In this model, there should be a strong multi-jet +etmiss signal from squark
pair production at the LHC. We find a 100 fb^{-1} reach of LHC out to
m_{3/2}\sim 118 TeV, corresponding to a gluino mass of \sim 2.6 TeV. A double
mass edge from the opposite-sign/same flavor dilepton invariant mass
distribution should be visible at LHC; this, along with the presence of short--
but visible-- highly ionizing tracks from quasi-stable charginos, should
provide a smoking gun signature for inoAMSB.Comment: 30 pages including 14 .eps figure
Neutralino versus axion/axino cold dark matter in the 19 parameter SUGRA model
We calculate the relic abundance of thermally produced neutralino cold dark
matter in the general 19 parameter supergravity (SUGRA-19) model. A scan over
GUT scale parameters reveals that models with a bino-like neutralino typically
give rise to a dark matter density \Omega_{\tz_1}h^2\sim 1-1000, i.e. between 1
and 4 orders of magnitude higher than the measured value. Models with higgsino
or wino cold dark matter can yield the correct relic density, but mainly for
neutralino masses around 700-1300 GeV. Models with mixed bino-wino or
bino-higgsino CDM, or models with dominant co-annihilation or A-resonance
annihilation can yield the correct abundance, but such cases are extremely hard
to generate using a general scan over GUT scale parameters; this is indicative
of high fine-tuning of the relic abundance in these cases. Requiring that
m_{\tz_1}\alt 500 GeV (as a rough naturalness requirement) gives rise to a
minimal probably dip in parameter space at the measured CDM abundance. For
comparison, we also scan over mSUGRA space with four free parameters. Finally,
we investigate the Peccei-Quinn augmented MSSM with mixed axion/axino cold dark
matter. In this case, the relic abundance agrees more naturally with the
measured value. In light of our cumulative results, we conclude that future
axion searches should probe much more broadly in axion mass, and deeper into
the axion coupling.Comment: 23 pages including 17 .eps figure
Vascular endothelial growth factor receptor-1 mediates migration of human colorectal carcinoma cells by activation of Src family kinases
Vascular endothelial growth factor (VEGF) is the predominant pro-angiogenic cytokine in human malignancy, and its expression correlates with disease recurrence and poor outcomes in patients with colorectal cancer. Recently, expression of vascular endothelial growth factor receptors (VEGFRs) has been observed on tumours of epithelial origin, including those arising in the colon, but the molecular mechanisms governing potential VEGF-driven biologic functioning in these tumours are not well characterised. In this report, we investigated the role of Src family kinases (SFKs) in VEGF-mediated signalling in human colorectal carcinoma (CRC) cell lines. Vascular endothelial growth factor specifically activated SFKs in HT29 and KM12L4 CRC cell lines. Further, VEGF stimulation resulted in enhanced cellular migration, which was effectively blocked by pharmacologic inhibition of VEGFR-1 or Src kinase. Correspondingly, migration studies using siRNA clones with reduced Src expression confirmed the requirement for Src in VEGF-induced migration in these cells. Furthermore, VEGF treatment enhanced VEGFR-1/SFK complex formation and increased tyrosine phosphorylation of focal adhesion kinase, p130 cas and paxillin. Finally, we demonstrate that VEGF-induced migration is not due, at least in part, to VEGF acting as a mitogen. These results suggest that VEGFR-1 promotes migration of tumour cells through a Src-dependent pathway linked to activation of focal adhesion components that regulate this process
- …