6,810 research outputs found
The General Warped Solution with Conical Branes in Six-dimensional Supergravity
We present the general regular warped solution with 4D Minkowski spacetime in
six-dimensional gauged supergravity. In this framework, we can easily embed
multiple conical branes into the warped geometry by choosing an undetermined
holomorphic function. As an example, for the holomorphic function with many
zeroes, we find warped solutions with multi-branes and discuss the generalized
flux quantization in this case.Comment: 1+19 pages, no figure, JHEP style, version to appear in JHE
Fast slow folding of an outer membrane porin
In comparison to globular proteins, the spontaneous folding and insertion of β-barrel membrane proteins are surprisingly slow, typically occurring on the order of minutes. Using single-molecule Förster resonance energy transfer to report on the folding of fluorescently labeled outer membrane protein G we measured the real-time insertion of a β-barrel membrane protein from an unfolded state. Folding events were rare and fast (<20 ms), occurring immediately upon arrival at the membrane. This combination of infrequent, but rapid, folding resolves this apparent dichotomy between slow ensemble kinetics and the typical timescales of biomolecular folding
Flux compactifications and supersymmetry breaking in 6D gauged supergravity
We review on a recent construction of the on-shell supersymmetric brane
action for the codimension-two branes with nonzero tension in the flux
compactification of a 6D chiral gauged supergravity. On dimesionally reducing
on 4D gauged supergravity for a new supersymmetric unwarped background with
conical branes, we consider the modulus stabilization for determining the soft
masses of the scalars localized on the branes and show that the bulk U(1)_R
provides a new mechanism for mediating the SUSY breaking.Comment: 12 pages, no figures, Invited review for Modern Physics Letters A,
Published versio
Captures of Red Giant Stars by Black Holes in Elliptical Galaxies: Feedback to the Hot Gas
The highly disturbed hot gas in elliptical galaxies, as revealed in many {\em
Chandra} X-ray images, implies a source of energy in the galactic nucleus. In
some elliptical galaxies faint X-ray ``ghost'' cavities appear without
corresponding radio lobes. It has been suggested that ghost cavities are caused
by short-lived activity with a timescale of years, but this is
difficult to understand within the popular paradigm of active galactic nuclei.
We suggest an episode model for ghost cavities, invoking captures of red giant
stars by the black hole located at the center of the elliptical galaxies at a
typical rate of yr per galaxy. The accretion of tidally
disrupted red giant stars onto the black hole powers activity in a timescale of
a few years. The total energy channeled into the jet/outflow during the cooling
time of the hot gas is erg, which is the typical work required
to form the observed cavities. In this scenario, the faint cavities are
produced by the feedback following accretion of the debris of the captured red
giant stars onto the black holes. We apply the present model to several
elliptical galaxies and find that it can explain the formation of the ghost
cavities. This model can be tested in the future by comparisons between radio
and X-ray observations.Comment: 4 pages in emulateapj5.sty. to Appear in ApJ Letter
Tunable Graphene Single Electron Transistor
We report electronic transport experiments on a graphene single electron
transistor. The device consists of a graphene island connected to source and
drain electrodes via two narrow graphene constrictions. It is electrostatically
tunable by three lateral graphene gates and an additional back gate. The
tunneling coupling is a strongly nonmonotonic function of gate voltage
indicating the presence of localized states in the barriers. We investigate
energy scales for the tunneling gap, the resonances in the constrictions and
for the Coulomb blockade resonances. From Coulomb diamond measurements in
different device configurations (i.e. barrier configurations) we extract a
charging energy of 3.4 meV and estimate a characteristic energy scale for the
constriction resonances of 10 meV.Comment: 6 pages and 5 figure
Supersymmetric codimension-two branes and U(1)_R mediation in 6D gauged supergravity
We construct a consistent supersymmetric action for brane chiral and vector
multiplets in a six-dimensional chiral gauged supergravity. A nonzero brane
tension can be accommodated by allowing for a brane-localized Fayet-Iliopoulos
term proportional to the brane tension. When the brane chiral multiplet is
charged under the bulk U(1)_R, we obtain a nontrivial coupling to the extra
component of the U(1)_R gauge field strength as well as a singular scalar
self-interaction term. Dimensionally reducing to 4D on a football
supersymmetric solution, we discuss the implication of such interactions for
obtaining the U(1)_R D-term in the 4D effective supergravity. By assuming the
bulk gaugino condensates and nonzero brane F- and/or D-term for the uplifting
potential, we have all the moduli stabilized with a vanishing cosmological
constant. The brane scalar with nonzero R charge then gets a soft mass of order
the gravitino mass. The overall sign of the soft mass squared depends on the
sign of the R charge as well as whether the brane F- or D-term dominates.Comment: 28 pages, no figures, version to appear in JHE
Interpolated wave functions for nonadiabatic simulations with the fixed-node quantum Monte Carlo method
Simulating nonadiabatic effects with many-body wave function approaches is an
open field with many challenges. Recent interest has been driven by new
algorithmic developments and improved theoretical understanding of properties
unique to electron-ion wave functions. Fixed-node diffusion Monte Caro is one
technique that has shown promising results for simulating electron-ion systems.
In particular, we focus on the CH molecule for which previous results suggested
a relatively significant contribution to the energy from nonadiabatic effects.
We propose a new wave function ansatz for diatomic systems which involves
interpolating the determinant coefficients calculated from configuration
interaction methods. We find this to be an improvement beyond previous wave
function forms that have been considered. The calculated nonadiabatic
contribution to the energy in the CH molecule is reduced compared to our
previous results, but still remains the largest among the molecules under
consideration.Comment: 7 pages, 3 figure
Cosmology of intersecting brane world models in Gauss-Bonnet gravity
We study the cosmological properties of a codimension two brane world that
sits at the intersection between two four branes, in the framework of six
dimensional Einstein-Gauss-Bonnet gravity. Due to contributions of the
Gauss-Bonnet terms, the junction conditions require the presence of localized
energy density on the codimension two defect. The induced metric on this
surface assumes a FRW form, with a scale factor associated to the position of
the brane in the background; we can embed on the codimension two defect the
preferred form of energy density. We present the cosmological evolution
equations for the three brane, showing that, for the case of pure AdS
backgrounds, they acquire the same form of the ones for the Randall-Sundrum II
model. When the background is different from pure AdS, the cosmological
behavior is potentially modified in respect to the typical one of codimension
one brane worlds. We discuss, in a particular model embedded in an AdS
black hole, the conditions one should satisfy in order to obtain standard
cosmology at late epochs.Comment: 19 pages, no figures, JHEP style. v2: Typos corrected and references
adde
Deep 1.1 mm-wavelength imaging of the GOODS-South field by AzTEC/ASTE -- II. Redshift distribution and nature of the submillimetre galaxy population
We report the results of the counterpart identification and a detailed
analysis of the physical properties of the 48 sources discovered in our deep
1.1mm wavelength imaging survey of the GOODS-South field using the AzTEC
instrument on the Atacama Submillimeter Telescope Experiment (ASTE). One or
more robust or tentative counterpart candidate is found for 27 and 14 AzTEC
sources, respectively, by employing deep radio continuum, Spitzer MIPS & IRAC,
and LABOCA 870 micron data. Five of the sources (10%) have two robust
counterparts each, supporting the idea that these galaxies are strongly
clustered and/or heavily confused. Photometric redshifts and star formation
rates (SFRs) are derived by analyzing UV-to-optical and IR-to-radio SEDs. The
median redshift of z~2.6 is similar to other earlier estimates, but we show
that 80% of the AzTEC-GOODS sources are at z>2, with a significant high
redshift tail (20% at z>3.3). Rest-frame UV and optical properties of AzTEC
sources are extremely diverse, spanning 10 magnitude in the i- and K-band
photometry with median values of i=25.3 and K=22.6 and a broad range of red
colour (i-K=0-6). These AzTEC sources are some of the most luminous galaxies in
the rest-frame optical bands at z>2, with inferred stellar masses of (1-30) x
10^{10} solar masses and UV-derived star formation rates of SFR(UV) > 10-1000
solar masses per year. The IR-derived SFR, 200-2000 solar masses per year, is
independent of redshift or stellar mass. The resulting specific star formation
rates, SSFR = 1-100 per Gyr, are 10-100 times higher than similar mass galaxies
at z=0, and they extend the previously observed rapid rise in the SSFR with
redshift to z=2-5. These galaxies have a SFR high enough to have built up their
entire stellar mass within their Hubble time. We find only marginal evidence
for an AGN contribution to the near-IR and mid-IR SEDs. (abridged)Comment: 31 pages including 14 figures, accepted for publication in the MNRAS.
A higher quality Figure 1 is also included as Figure1.jp
- …