5,616 research outputs found
New Predictions for Electroweak O(\alpha) Corrections to Neutrino--Nucleon Scattering
We calculate the O(\alpha) electroweak corrections to charged- and
neutral-current deep-inelastic neutrino scattering off an isoscalar target. The
full one-loop-corrected cross sections, including hard photonic corrections,
are evaluated and compared to an earlier result which is the basis of the NuTeV
analysis. In particular, we compare results that differ in input-parameter
scheme, treatment of real photon radiation and factorization scheme. The
associated shifts in the theoretical prediction for the ratio of neutral- and
charged-current cross sections can be larger than the experimental accuracy of
the NuTeV result.Comment: 3 pages, in collaboration with S. Dittmaier and W. Hollik,
proceedings contribution to International Europhysics Conference on High
Energy Physics, EPS (July 17th-23rd 2003) in Aachen, German
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
A new general purpose event horizon finder for 3D numerical spacetimes
I present a new general purpose event horizon finder for full 3D numerical spacetimes. It works by evolving a complete null surface backwards in time. The null surface is described as the zero level set of a scalar function, that in principle is defined everywhere. This description of the surface allows the surface, trivially, to change topology, making this event horizon finder able to handle numerical spacetimes, where two (or more) black holes merge into a single final black hole
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