1,507 research outputs found
Non-perturbative behavior of the quantum phase transition to a nematic Fermi fluid
We discuss shape (Pomeranchuk) instabilities of the Fermi surface of a
two-dimensional Fermi system using bosonization. We consider in detail the
quantum critical behavior of the transition of a two dimensional Fermi fluid to
a nematic state which breaks spontaneously the rotational invariance of the
Fermi liquid. We show that higher dimensional bosonization reproduces the
quantum critical behavior expected from the Hertz-Millis analysis, and verify
that this theory has dynamic critical exponent . Going beyond this
framework, we study the behavior of the fermion degrees of freedom directly,
and show that at quantum criticality as well as in the the quantum nematic
phase (except along a set of measure zero of symmetry-dictated directions) the
quasi-particles of the normal Fermi liquid are generally wiped out. Instead,
they exhibit short ranged spatial correlations that decay faster than any
power-law, with the law and we
verify explicitely the vanishing of the fermion residue utilizing this
expression. In contrast, the fermion auto-correlation function has the behavior
. In this regime we also find that, at
low frequency, the single-particle fermion density-of-states behaves as
, where is larger
than the free Fermi value, N(0), and is a constant. These results confirm
the non-Fermi liquid nature of both the quantum critical theory and of the
nematic phase.Comment: 20 pages, 2 figures, 1 table; new version with minor changes; new
subsection 3C2 added with an explicit calculation of the quasiparticle
residue at the nematic transition; minor typos corrected, new references;
general beautification of the text and figure
Renormalization Group Approach to the Normal State of Copper-Oxide Superconductors
We study by means of renormalization group techniques the effect that on the
two-dimensional electron liquid may have the van Hove singularities observed
experimentally in the copper-oxide superconductors. We find significant
deviations from Fermi liquid behavior, that lead to the appearance of an
unstable fixed point in the renormalization group flow of the effective
coupling constant. Besides the attenuation of electron quasiparticles already
known on phenomenological grounds, our approach is able to explain the
reduction in the dispersion of the band as well as the pinning of the Fermi
level near the singularity, as observed in the photoemission experiments.Comment: Latex manuscript, 29 pages, 4 postcript figure
A scattering theory of ultrarelativistic solitons
We construct a perturbative framework for understanding the collision of
solitons (more precisely, solitary waves) in relativistic scalar field
theories. Our perturbative framework is based on the suppression of the
space-time interaction area proportional to , where is the
relative velocity of an incoming solitary wave and . We calculate the leading order results for collisions of (1+1) dimensional
kinks in periodic potentials, and provide explicit, closed form expressions for
the phase shift and the velocity change after the collisions. We find excellent
agreement between our results and detailed numerical simulations. Crucially,
our perturbation series is controlled by a kinematic parameter, and hence not
restricted to small deviations around integrable cases such as the Sine-Gordon
model.Comment: v3: 43 pages, 10 figures, references added, matches version accepted
for publication in PR
Parity Violating Measurements of Neutron Densities
Parity violating electron nucleus scattering is a clean and powerful tool for
measuring the spatial distributions of neutrons in nuclei with unprecedented
accuracy. Parity violation arises from the interference of electromagnetic and
weak neutral amplitudes, and the of the Standard Model couples primarily
to neutrons at low . The data can be interpreted with as much confidence
as electromagnetic scattering. After briefly reviewing the present theoretical
and experimental knowledge of neutron densities, we discuss possible parity
violation measurements, their theoretical interpretation, and applications. The
experiments are feasible at existing facilities. We show that theoretical
corrections are either small or well understood, which makes the interpretation
clean. The quantitative relationship to atomic parity nonconservation
observables is examined, and we show that the electron scattering asymmetries
can be directly applied to atomic PNC because the observables have
approximately the same dependence on nuclear shape.Comment: 38 pages, 7 ps figures, very minor changes, submitted to Phys. Rev.
Classical Dynamics of Vortex Solitons from Perturbative Scattering Amplitudes
We introduce a novel point-particle effective description of ANO vortex
solitons in the critical Abelian Higgs Model (AHM) in based on the
small winding expansion. Identifying the effective vortices with the elementary
quanta of a complex scalar field, relativistic vortex-vortex scattering
amplitudes are calculated as a diagrammatic, perturbative expansion in the
winding number . Making use of powerful techniques recently developed for
analyzing the post-Minkowskian two-body problem in general relativity, we
efficiently extract the contribution to the loop integrals from the classical
potential region, with the resulting velocity expansion subsequently resummed
to all orders. The main result of this paper is an analytic expression for the
classical, vortex-vortex potential at , or
one-loop, with exact velocity dependence. By truncating the resulting effective
Hamiltonian at we derive an analytic,
perturbative expression for the metric on the 2-vortex moduli space. Finally,
the emergence of the critical AHM from the classical limit of the
supersymmetric AHM, and the resulting constraints on the
point-particle EFT is described in detail using an on-shell superspace
construction for BPS states in .Comment: 40 pages, 8 figure
Testing Lorentz invariance of dark matter with satellite galaxies
We develop the framework for testing Lorentz invariance in the dark matter
sector using galactic dynamics. We consider a Lorentz violating (LV) vector
field acting on the dark matter component of a satellite galaxy orbiting in a
host halo. We introduce a numerical model for the dynamics of satellites in a
galactic halo and for a galaxy in a rich cluster to explore observational
consequences of such an LV field. The orbital motion of a satellite excites a
time dependent LV force which greatly affects its internal dynamics. Our
analysis points out key observational signatures which serve as probes of LV
forces. These include modifications to the line of sight velocity dispersion,
mass profiles and shapes of satellites. With future data and a more detailed
modeling these signatures can be exploited to constrain a new region of the
parameter space describing the LV in the dark matter sector.Comment: 27 pages, 11 figures, 2 tables, 1 appendix. Minor corrections in
section 4.3.
Beyond the Cosmological Standard Model
After a decade and a half of research motivated by the accelerating universe,
theory and experiment have a reached a certain level of maturity. The
development of theoretical models beyond \Lambda, or smooth dark energy, often
called modified gravity, has led to broader insights into a path forward, and a
host of observational and experimental tests have been developed. In this
review we present the current state of the field and describe a framework for
anticipating developments in the next decade. We identify the guiding
principles for rigorous and consistent modifications of the standard model, and
discuss the prospects for empirical tests. We begin by reviewing attempts to
consistently modify Einstein gravity in the infrared, focusing on the notion
that additional degrees of freedom introduced by the modification must screen
themselves from local tests of gravity. We categorize screening mechanisms into
three broad classes: mechanisms which become active in regions of high
Newtonian potential, those in which first derivatives become important, and
those for which second derivatives are important. Examples of the first class,
such as f(R) gravity, employ the familiar chameleon or symmetron mechanisms,
whereas examples of the last class are galileon and massive gravity theories,
employing the Vainshtein mechanism. In each case, we describe the theories as
effective theories. We describe experimental tests, summarizing laboratory and
solar system tests and describing in some detail astrophysical and cosmological
tests. We discuss future tests which will be sensitive to different signatures
of new physics in the gravitational sector. Parts that are more relevant to
theorists vs. observers/experimentalists are clearly indicated, in the hope
that this will serve as a useful reference for both audiences, as well as
helping those interested in bridging the gap between them.Comment: 175 pages, 24 figures. v2: Minor corrections, added references.
Review article, comments welcom
Precision constraints on radiative neutrino decay with CMB spectral distortion
We investigate the radiative decay of the cosmic neutrino background, and its
impact on the spectrum of the cosmic microwave background (CMB) that is known
to be a nearly perfect black body. We derive exact formulae for the decay of a
heavier neutrino into a lighter neutrino and a photon, , and of absorption as its inverse, , by
accounting for the precise form of the neutrino momentum distribution. Our
calculations show that if the neutrinos are heavier than eV,
the exact formulae give results that differ by 50%, compared with
approximate ones where neutrinos are assumed to be at rest. We also find that
spectral distortion due to absorption is more important for heavy neutrino
masses (by a factor of 10 going from a neutrino mass of 0.01 eV to 0.1
eV). By analyzing the CMB spectral data measured with COBE-FIRAS, we obtain
lower limits on the neutrino lifetime of s
(95% C.L.) for the smaller mass splitting and s for the larger mass splitting. These represent up to one order of
magnitude improvement over previous CMB constraints. With future CMB
experiments such as PIXIE, these limits will improve by roughly 4 orders of
magnitude. This translates to a projected upper limit on the neutrino magnetic
moment (for certain neutrino masses and decay modes) of , where is the Bohr magneton. Such constraints would
make future precision CMB measurements competitive with lab-based constraints
on neutrino magnetic moments.Comment: 14 pages, 9 figures. v2: Added a number of references and
clarifications. Matches version published in PR
Early-Time Energy Loss in a Strongly-Coupled SYM Plasma
We carry out an analytic study of the early-time motion of a quark in a
strongly-coupled maximally-supersymmetric Yang-Mills plasma, using the AdS/CFT
correspondence. Our approach extracts the first thermal effects as a small
perturbation of the known quark dynamics in vacuum, using a double expansion
that is valid for early times and for (moderately) ultrarelativistic quark
velocities. The quark is found to lose energy at a rate that differs
significantly from the previously derived stationary/late-time result: it
scales like T^4 instead of T^2, and is associated with a friction coefficient
that is not independent of the quark momentum. Under conditions representative
of the quark-gluon plasma as obtained at RHIC, the early energy loss rate is a
few times smaller than its late-time counterpart. Our analysis additionally
leads to thermally-corrected expressions for the intrinsic energy and momentum
of the quark, in which the previously discovered limiting velocity of the quark
is found to appear naturally.Comment: 39 pages, no figures. v2: Minor corrections and clarifications.
References added. Version to be published in JHE
Proceedings of the 3rd Annual Conference on Aerospace Computational Control, volume 1
Conference topics included definition of tool requirements, advanced multibody component representation descriptions, model reduction, parallel computation, real time simulation, control design and analysis software, user interface issues, testing and verification, and applications to spacecraft, robotics, and aircraft
- …