7,535 research outputs found
Self-Tuning at Large (Distances): 4D Description of Runaway Dilaton Capture
We complete here a three-part study (see also arXiv:1506.08095 and
1508.00856) of how codimension-two objects back-react gravitationally with
their environment, with particular interest in situations where the transverse
`bulk' is stabilized by the interplay between gravity and flux-quantization in
a dilaton-Maxwell-Einstein system such as commonly appears in
higher-dimensional supergravity and is used in the Supersymmetric Large Extra
Dimensions (SLED) program. Such systems enjoy a classical flat direction that
can be lifted by interactions with the branes, giving a mass to the would-be
modulus that is smaller than the KK scale. We construct the effective
low-energy 4D description appropriate below the KK scale once the transverse
extra dimensions are integrated out, and show that it reproduces the
predictions of the full UV theory for how the vacuum energy and modulus mass
depend on the properties of the branes and stabilizing fluxes. In particular we
show how this 4D theory learns the news of flux quantization through the
existence of a space-filling four-form potential that descends from the
higher-dimensional Maxwell field. We find a scalar potential consistent with
general constraints, like the runaway dictated by Weinberg's theorem. We show
how scale-breaking brane interactions can give this potential minima for which
the extra-dimensional size, , is exponentially large relative to
underlying physics scales, , with where
can be arranged with a small hierarchy between fundamental
parameters. We identify circumstances where the potential at the minimum can
(but need not) be parametrically suppressed relative to the tensions of the
branes, provide a preliminary discussion of the robustness of these results to
quantum corrections, and discuss the relation between what we find and earlier
papers in the SLED program.Comment: 37 pages + appendice
The Gravity of Dark Vortices: Effective Field Theory for Branes and Strings Carrying Localized Flux
A Nielsen-Olesen vortex usually sits in an environment that expels the flux
that is confined to the vortex, so flux is not present both inside and outside.
We construct vortices for which this is not true, where the flux carried by the
vortex also permeates the `bulk' far from the vortex. The idea is to mix the
vortex's internal gauge flux with an external flux using off-diagonal kinetic
mixing. Such `dark' vortices could play a phenomenological role in models with
both cosmic strings and a dark gauge sector. When coupled to gravity they also
provide explicit ultra-violet completions for codimension-two brane-localized
flux, which arises in extra-dimensional models when the same flux that
stabilizes extra-dimensional size is also localized on space-filling branes
situated around the extra dimensions. We derive simple formulae for observables
such as defect angle, tension, localized flux and on-vortex curvature when
coupled to gravity, and show how all of these are insensitive to much of the
microscopic details of the solutions, and are instead largely dictated by
low-energy quantities. We derive the required effective description in terms of
a world-sheet brane action, and derive the matching conditions for its
couplings. We consider the case where the dimensions transverse to the bulk
compactify, and determine how the on- and off-vortex curvatures and other bulk
features depend on the vortex properties. We find that the brane-localized flux
does not gravitate, but just renormalizes the tension in a magnetic-field
independent way. The existence of an explicit UV completion puts the effective
description of these models on a more precise footing, verifying that
brane-localized flux can be consistent with sensible UV physics and resolving
some apparent paradoxes that can arise with a naive (but commonly used)
delta-function treatment of the brane's localization within the bulk.Comment: 36 pages + appendices, 7 figure
EFT for Vortices with Dilaton-dependent Localized Flux
We study how codimension-two objects like vortices back-react gravitationally
with their environment in theories (such as 4D or higher-dimensional
supergravity) where the bulk is described by a dilaton-Maxwell-Einstein system.
We do so both in the full theory, for which the vortex is an explicit classical
`fat brane' solution, and in the effective theory of `point branes' appropriate
when the vortices are much smaller than the scales of interest for their
back-reaction (such as the transverse Kaluza-Klein scale). We extend the
standard Nambu-Goto description to include the physics of flux-localization
wherein the ambient flux of the external Maxwell field becomes partially
localized to the vortex, generalizing the results of a companion paper to
include dilaton-dependence for the tension and localized flux. In the effective
theory, such flux-localization is described by the next-to-leading effective
interaction, and the boundary conditions to which it gives rise are known to
play an important role in how (and whether) the vortex causes supersymmetry to
break in the bulk. We track how both tension and localized flux determine the
curvature of the space-filling dimensions. Our calculations provide the tools
required for computing how scale-breaking vortex interactions can stabilize the
extra-dimensional size by lifting the dilaton's flat direction. For small
vortices we derive a simple relation between the near-vortex boundary
conditions of bulk fields as a function of the tension and localized flux in
the vortex action that provides the most efficient means for calculating how
physical vortices mutually interact without requiring a complete construction
of their internal structure. In passing we show why a common procedure for
doing so using a -function can lead to incorrect results. Our
procedures generalize straightforwardly to general co-dimension objects.Comment: 45 pages + appendix, 6 figure
Sensing Subjective Well-being from Social Media
Subjective Well-being(SWB), which refers to how people experience the quality
of their lives, is of great use to public policy-makers as well as economic,
sociological research, etc. Traditionally, the measurement of SWB relies on
time-consuming and costly self-report questionnaires. Nowadays, people are
motivated to share their experiences and feelings on social media, so we
propose to sense SWB from the vast user generated data on social media. By
utilizing 1785 users' social media data with SWB labels, we train machine
learning models that are able to "sense" individual SWB from users' social
media. Our model, which attains the state-by-art prediction accuracy, can then
be used to identify SWB of large population of social media users in time with
very low cost.Comment: 12 pages, 1 figures, 2 tables, 10th International Conference, AMT
2014, Warsaw, Poland, August 11-14, 2014. Proceeding
Cryogenic Calibration Setup for Broadband Complex Impedance Measurements
Reflection measurements give access to the complex impedance of a material on
a wide frequency range. This is of interest to study the dynamical properties
of various materials, for instance disordered superconductors. However
reflection measurements made at cryogenic temperature suffer from the
difficulty to reliably subtract the circuit contribution. Here we report on the
design and first tests of a setup able to precisely calibrate in situ the
sample reflection, at 4.2 K and up to 2 GHz, by switching and measuring, during
the same cool down, the sample and three calibration standards.Comment: (6 pages, 6 figures
LHC and dark matter signals of Z' bosons
We customize the simulation code FEWZ (Fully Exclusive W, Z Production) to
study Z' production at the LHC for both \sqrt{s}=8 TeV and 14 TeV. Using the
results of our simulation for several standard benchmark Z' models, we derive a
semi-empirical expression for the differential cross section, that permits the
determination of Z' couplings in a model-independent manner. We evaluate cross
sections and other observables for large classes of models, including the
common E_6, left-right and B-L models, as a function of model parameters. We
also consider a hidden sector Z' that couples to standard model fermions via
kinetic and mass mixing and serves as a mediator of isospin-violating
interactions with dark matter. We combine the results of LHC Z' searches and
dark matter direct detection experiments with global electroweak data to obtain
mass-dependent constraints on the model parameters.Comment: 30 pages, 19 figures, 2 tables. Published versio
Local Current Distribution and "Hot Spots" in the Integer Quantum Hall Regime
In a recent experiment, the local current distribution of a two-dimensional
electron gas in the quantum Hall regime was probed by measuring the variation
of the conductance due to local gating. The main experimental finding was the
existence of "hot spots", i.e. regions with high degree of sensitivity to local
gating, whose density increases as one approaches the quantum Hall transition.
However, the direct connection between these "hot spots" and regions of high
current flow is not clear. Here, based on a recent model for the quantum Hall
transition consisting of a mixture of perfect and quantum links, the relation
between the "hot spots" and the current distribution in the sample has been
investigated. The model reproduces the observed dependence of the number and
sizes of "hot spots" on the filling factor. It is further demonstrated that
these "hot spots" are not located in regions where most of the current flows,
but rather, in places where the currents flow both when injected from the left
or from the right. A quantitative measure, the harmonic mean of these currents
is introduced and correlates very well with the "hot spots" positions
Dynamical mean-field equations for strongly interacting fermionic atoms in a potential trap
We derive a set of dynamical mean-field equations for strongly interacting
fermionic atoms in a potential trap across a Feshbach resonance. Our derivation
is based on a variational ansatz, which generalizes the crossover wavefunction
to the inhomogeneous case, and the assumption that the order parameter is
slowly varying over the size of the Cooper pairs. The equations reduce to a
generalized time-dependent Gross-Pitaevskii equation on the BEC side of the
resonance. We discuss an iterative method to solve these mean-field equations,
and present the solution for a harmonic trap as an illustrating example to
self-consistently verify the approximations made in our derivation.Comment: replaced with the published versio
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