2,655 research outputs found
Desensitizing Inflation from the Planck Scale
A new mechanism to control Planck-scale corrections to the inflationary eta
parameter is proposed. A common approach to the eta problem is to impose a
shift symmetry on the inflaton field. However, this symmetry has to remain
unbroken by Planck-scale effects, which is a rather strong requirement on
possible ultraviolet completions of the theory. In this paper, we show that the
breaking of the shift symmetry by Planck-scale corrections can be
systematically suppressed if the inflaton field interacts with a conformal
sector. The inflaton then receives an anomalous dimension in the conformal
field theory, which leads to sequestering of all dangerous high-energy
corrections. We analyze a number of models where the mechanism can be seen in
action. In our most detailed example we compute the exact anomalous dimensions
via a-maximization and show that the eta problem can be solved using only
weakly-coupled physics.Comment: 34 pages, 3 figures
Mathematical description of bacterial traveling pulses
The Keller-Segel system has been widely proposed as a model for bacterial
waves driven by chemotactic processes. Current experiments on {\em E. coli}
have shown precise structure of traveling pulses. We present here an
alternative mathematical description of traveling pulses at a macroscopic
scale. This modeling task is complemented with numerical simulations in
accordance with the experimental observations. Our model is derived from an
accurate kinetic description of the mesoscopic run-and-tumble process performed
by bacteria. This model can account for recent experimental observations with
{\em E. coli}. Qualitative agreements include the asymmetry of the pulse and
transition in the collective behaviour (clustered motion versus dispersion). In
addition we can capture quantitatively the main characteristics of the pulse
such as the speed and the relative size of tails. This work opens several
experimental and theoretical perspectives. Coefficients at the macroscopic
level are derived from considerations at the cellular scale. For instance the
stiffness of the signal integration process turns out to have a strong effect
on collective motion. Furthermore the bottom-up scaling allows to perform
preliminary mathematical analysis and write efficient numerical schemes. This
model is intended as a predictive tool for the investigation of bacterial
collective motion
Baryonic symmetries and M5 branes in the AdS_4/CFT_3 correspondence
We study U(1) symmetries dual to Betti multiplets in the AdS_4/CFT_3
correspondence for M2 branes at Calabi-Yau four-fold singularities. Analysis of
the boundary conditions for vector fields in AdS_4 allows for a choice where
wrapped M5 brane states carrying non-zero charge under such symmetries can be
considered. We begin by focusing on isolated toric singularities without
vanishing six-cycles, and study in detail the cone over Q^{111}. The boundary
conditions considered are dual to a CFT where the gauge group is U(1)^2 x
SU(N)^4. We find agreement between the spectrum of gauge-invariant
baryonic-type operators in this theory and wrapped M5 brane states. Moreover,
the physics of vacua in which these symmetries are spontaneously broken
precisely matches a dual gravity analysis involving resolutions of the
singularity, where we are able to match condensates of the baryonic operators,
Goldstone bosons and global strings. We also argue more generally that theories
where the resolutions have six-cycles are expected to receive non-perturbative
corrections from M5 brane instantons. We give a general formula relating the
instanton action to normalizable harmonic two-forms, and compute it explicitly
for the Q^{222} example. The holographic interpretation of such instantons is
currently unclear.Comment: 92 pages, 10 figure
Holographic Renormalization and Stress Tensors in New Massive Gravity
We obtain holographically renormalized boundary stress tensors with the
emphasis on a special point in the parameter space of three dimensional new
massive gravity, using the so-called Fefferman-Graham coordinates with relevant
counter terms. Through the linearized equations of motion with a standard
prescription, we also obtain correlators among these stress tensors. We argue
that the self-consistency of holographic renormalization determines counter
terms up to unphysical ambiguities. Using these renormalized stress tensors in
Fefferman-Graham coordinates, we obtain the central charges of dual CFT, and
mass and angular momentum of some black hole solutions. These results are
consistent with the previous ones obtained by other methods. In this study on
the Fefferman-Graham expansion of new massive gravity, some aspects of higher
curvature gravity are revealed.Comment: Version accepted for publication in JHEP, conclusion revised,
references adde
Simultaneous determination of natural and synthetic steroid estrogens and their conjugates in aqueous matrices by liquid chromatography / mass spectrometry
An analytical method for the simultaneous determination of nine free and conjugated steroid estrogens was developed with application to environmental aqueous matrices. Solid phase extraction (SPE) was employed for isolation and concentration, with detection by liquid chromatography/mass spectrometry (LC/MS) using electrospray ionisation (ESI) in the negative mode. Method recoveries for various aqueous matrices (wastewater, lake and drinking water) were determined, recoveries proving to be sample dependent. When spiked at 50 ng/l concentrations in sewage influent, recoveries ranged from 62-89 % with relative standard deviations (RSD) < 8.1 %. In comparison, drinking water spiked at the same concentrations had recoveries between 82-100 % with an RSD < 5%. Ion suppression is a known phenomenon when using ESI; hence its impact on method recovery was elucidated for raw sewage. Both ion suppression from matrix interferences and the extraction procedure has bearing on the overall method recovery. Analysis of municipal raw sewage identified several of the analytes of interest at ng/l concentrations, estriol (E3) being the most abundant. Only one conjugate, estrone 3-sulphate (E1-3S) was observe
A Novel Unsupervised Method to Identify Genes Important in the Anti-viral Response: Application to Interferon/Ribavirin in Hepatitis C Patients
Background: Treating hepatitis C with interferon/ribavirin results in a varied response in terms of decrease in viral titer and ultimate outcome. Marked responders have a sharp decline in viral titer within a few days of treatment initiation, whereas in other patients there is no effect on the virus (poor responders). Previous studies have shown that combination therapy modifies expression of hundreds of genes in vitro and in vivo. However, identifying which, if any, of these genes have a role in viral clearance remains challenging. Aims: The goal of this paper is to link viral levels with gene expression and thereby identify genes that may be responsible for early decrease in viral titer. Methods: Microarrays were performed on RNA isolated from PBMC of patients undergoing interferon/ribavirin therapy. Samples were collected at pre-treatment (day 0), and 1, 2, 7, 14 and 28 days after initiating treatment. A novel method was applied to identify genes that are linked to a decrease in viral titer during interferon/ribavirin treatment. The method uses the relationship between inter-patient gene expression based proximities and inter-patient viral titer based proximities to define the association between microarray gene expression measurements of each gene and viral-titer measurements. Results: We detected 36 unique genes whose expressions provide a clustering of patients that resembles viral titer based clustering of patients. These genes include IRF7, MX1, OASL and OAS2, viperin and many ISG's of unknown function. Conclusion: The genes identified by this method appear to play a major role in the reduction of hepatitis C virus during the early phase of treatment. The method has broad utility and can be used to analyze response to any group of factors influencing biological outcome such as antiviral drugs or anti-cancer agents where microarray data are available. © 2007 Brodsky et al
Non-perturbative Vacuum Destabilization and D-brane Dynamics
We analyze the process of string vacuum destabilization due to instanton
induced superpotential couplings which depend linearly on charged fields. These
non-perturbative instabilities result in potentials for the D-brane moduli and
lead to processes of D-brane recombination, motion and partial moduli
stabilization at the non-perturbative vacuum. By using techniques of D-brane
instanton calculus, we explicitly compute this scalar potential in toroidal
orbifold compactifications with magnetized D-branes by summing over the
possible discrete instanton configurations. We illustrate explicitly the
resulting dynamics in globally consistent models. These instabilities can have
phenomenological applications to breaking hidden sector gauge groups, open
string moduli stabilization and supersymmetry breaking. Our results suggest
that breaking supersymmetry by Polonyi-like models in string theory is more
difficult than expected.Comment: 61 pages, 6 figures, 5 tables; Minor corrections, version published
in JHE
What happens if you single out? An experiment
We present an experiment investigating the effects of singling out an individual on trust and trustworthiness. We find that (a) trustworthiness falls if there is a singled out subject; (b) non-singled out subjects discriminate against the singled out subject when they are not responsible of the distinct status of this person; (c) under a negative frame, the singled out subject returns significantly less; (d) under a positive frame, the singled out subject behaves bimodally, either selecting very low or very high return rates. Overall, singling out induces a negligible effect on trust but is potentially disruptive for trustworthiness
Transiting Disintegrating Planetary Debris around WD 1145+017
More than a decade after astronomers realized that disrupted planetary
material likely pollutes the surfaces of many white dwarf stars, the discovery
of transiting debris orbiting the white dwarf WD 1145+017 has opened the door
to new explorations of this process. We describe the observational evidence for
transiting planetary material and the current theoretical understanding (and in
some cases lack thereof) of the phenomenon.Comment: Invited review chapter. Accepted March 23, 2017 and published October
7, 2017 in the Handbook of Exoplanets. 15 pages, 10 figure
D3-brane Potentials from Fluxes in AdS/CFT
We give a comprehensive treatment of the scalar potential for a D3-brane in a
warped conifold region of a compactification with stabilized moduli. By
studying general ultraviolet perturbations in supergravity, we systematically
incorporate `compactification effects' sourced by supersymmetry breaking in the
compact space. Significant contributions to the D3-brane potential, including
the leading term in the infrared, arise from imaginary anti-self-dual (IASD)
fluxes. For an arbitrary Calabi-Yau cone, we determine the most general IASD
fluxes in terms of scalar harmonics, then compute the resulting D3-brane
potential. Specializing to the conifold, we identify the operator dual to each
mode of flux, and for chiral operators we confirm that the potential computed
in the gauge theory matches the gravity result. The effects of four-dimensional
curvature, including the leading D3-brane mass term, arise directly from the
ten-dimensional equations of motion. Furthermore, we show that gaugino
condensation on D7-branes provides a local source for IASD flux. This flux
precisely encodes the nonperturbative contributions to the D3-brane potential,
yielding a promising ten-dimensional representation of four-dimensional
nonperturbative effects. Our result encompasses all significant contributions
to the D3-brane potential discussed in the literature, and does so in the
single coherent framework of ten-dimensional supergravity. Moreover, we
identify new terms with irrational scaling dimensions that were inaccessible in
prior works. By decoupling gravity in a noncompact configuration, then
systematically reincorporating compactification effects as ultraviolet
perturbations, we have provided an approach in which Planck-suppressed
contributions to the D3-brane effective action can be computed.Comment: 70 page
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