3,686 research outputs found
Cardiac reserve during weightlessness simulation and shuttle flight
Bedrest deconditioning is suspected to reduce cardiac function. However, quantitation of subtle decreases in cardiac reserve may be difficult. Normal subjects show considerable variability in heart rate response, reflected by a relatively broadband interbeat interval power spectrum. We hypothesized that the deconditioning effects of bedrest would induce narrowing of this spectrum, reflecting a reduction in the autonomically-modulated variability in heart rate. Ten aerobically conditioned men (average 35-50 years) underwent orthostatic tolerance testing with lower body negative pressure pre-bedrest and after 10 days of bedrest, while on placebo and after intravenous atropine. Spectra were derived by Fourier analysis of 128 interbeat interval data sets from subjects with sufficient numbers of beats during matched periods of the protocol. Data suggest that atropine unmasks the deconditioning effect of bedrest in athletic men, evidenced by a reduction in interbeat interval spectral power compared with placebo. Spectral analysis offers a new means of quantitating the effects of bedrest deconditioning and autonomic perturbations on cardiac dynamics
Modern Dynamical Coupled-Channels Calculations for Extracting and Understanding the Nucleon Spectrum
We give an overview of recent progress in the spectroscopic study of nucleon
resonances within the dynamical coupled-channels analysis of meson-production
reactions. The important role of multichannel reaction dynamics in
understanding various properties of nucleon resonances is emphasized.Comment: 11 pages, 8 figures. Plenary talk at The 14th International
Conference on Meson-Nucleon Physics and the Structure of the Nucleon
(MENU2016), Kyoto, Japan, July 25-30, 201
Gauge coupling renormalization in RS1
We compute the 4D low energy effective gauge coupling at one-loop order in
the compact Randall-Sundrum scenario with bulk gauge fields and charged matter,
within controlled approximations. While such computations are subtle, they can
be important for studying phenomenological issues such as grand unification.
Ultraviolet divergences are cut-off using Pauli-Villars regularization so as to
respect 5D gauge and general coordinate invariance. The structure of these
divergences on branes and in the bulk is elucidated by a 5D position-space
analysis. The remaining finite contributions are obtained by a careful analysis
of the Kaluza-Klein spectrum. We comment on the agreement between our results
and expectations based on the AdS/CFT correspondence, in particular logarithmic
sensitivity to the 4D Planck scale.Comment: 17 pages, Latex2e, uses axodraw.sty, new references added. To be
published in Nucl. Phys.
The Delocalized Effective Degrees of Freedom of a Black Hole at Low Frequencies
Identifying the fundamental degrees of freedom of a black hole poses a
long-standing puzzle. In hep-th/0511133 Goldberger and Rothstein forwarded a
theory of the low frequency degrees of freedom within the effective field
theory approach, where they are relevancy-ordered but of unclear physical
origin. Here these degrees of freedom are identified with near-horizon but
non-compact gravitational perturbations which are decomposed into delocalized
multipoles. Their world-line (kinetic) action is determined within the
classical effective field theory (CLEFT) approach and their interactions are
discussed. The case of the long-wavelength scattering of a scalar wave off a
Schwarzschild black hole is treated in some detail, interpreting within the
CLEFT approach the equality of the leading absorption cross section with the
horizon area.Comment: 8 pages. Awarded fifth prize in the 2008 Gravity Research Foundation
essay contest. v2: minor change
Dynamical Entanglement in Particle Scattering
This paper explores the connections between particle scattering and quantum
information theory in the context of the non-relativistic, elastic scattering
of two spin-1/2 particles. An untangled, pure, two-particle in-state is evolved
by an S-matrix that respects certain symmetries and the entanglement of the
pure out-state is measured. The analysis is phrased in terms of unitary,
irreducible representations (UIRs) of the symmetry group in question, either
the rotation group for the spin degrees of freedom or the Galilean group for
non-relativistic particles. Entanglement may occurs when multiple UIRs appear
in the direct sum decomposition of the direct product in-state, but it also
depends of the scattering phase shifts. \keywords{dynamical entanglement,
scattering, Clebsch-Gordan methods}Comment: 6 pages, submitted to Int. J. Mod. Phys. A as part of MRST 2005
conference proceeding
Gravity and antigravity in a brane world with metastable gravitons : Comment on hep-th/0002190 and hep-th/0003020
In the framework of a five-dimensional three-brane model with quasi-localized
gravitons we evaluate metric perturbations induced on the positive tension
brane by matter residing thereon. We find that at intermediate distances, the
effective four-dimensional theory coincides, up to small corrections, with
General Relativity. This is in accord with Csaki, Erlich and Hollowood and in
contrast to Dvali, Gabadadze and Porrati. We show, however, that at ultra-large
distances this effective four-dimensional theory becomes dramatically
different: conventional tensor gravity changes into scalar anti-gravity.Comment: 6 pages revtex, tex corrected, this paper should be read in tandem
with hep-th/000207
Light scalar at LHC: the Higgs or the dilaton?
It is likely that the LHC will observe a color- and charge-neutral scalar
whose decays are consistent with those of the Standard Model (SM) Higgs boson.
The Higgs interpretation of such a discovery is not the only possibility. For
example, electroweak symmetry breaking (EWSB) could be triggered by a
spontaneously broken, nearly conformal sector. The spectrum of states at the
electroweak scale would then contain a narrow scalar resonance, the
pseudo-Goldstone boson of conformal symmetry breaking, with Higgs-like
properties. If the conformal sector is strongly coupled, this pseudo-dilaton
may be the only new state accessible at high energy colliders. We discuss the
prospects for distinguishing this mode from a minimal Higgs boson at the LHC
and ILC. The main discriminants between the two scenarios are (1) cubic
self-interactions and (2) a potential enhancement of couplings to massless SM
gauge bosons. A particularly interesting situation arises when the scale f of
conformal symmetry breaking is approximately the electroweak scale v~246 GeV.
Although in this case the LHC may not be able to tell apart a pseudo-dilaton
from the Higgs boson, the self-interactions differ in a way that depends only
on the scaling dimension of certain operators in the conformal sector. This
opens the possibility of using dilaton pair production at future colliders as a
probe of EWSB induced by nearly conformal new physics.Comment: 7 pages, LaTe
Natural entropy fluctuations discriminate similar looking electric signals emitted from systems of different dynamics
Complexity measures are introduced, that quantify the change of the natural
entropy fluctuations at different length scales in time-series emitted from
systems operating far from equilibrium. They identify impending sudden cardiac
death (SD) by analyzing fifteen minutes electrocardiograms, and comparing to
those of truly healthy humans (H). These measures seem to be complementary to
the ones suggested recently [Phys. Rev. E {\bf 70}, 011106 (2004)] and
altogether enable the classification of individuals into three categories: H,
heart disease patients and SD. All the SD individuals, who exhibit critical
dynamics, result in a common behavior.Comment: Published in Physical Review
How to reconcile the Rosenbluth and the polarization transfer method in the measurement of the proton form factors
The apparent discrepancy between the Rosenbluth and the polarization transfer
method for the ratio of the electric to magnetic proton form factors can be
explained by a two-photon exchange correction which does not destroy the
linearity of the Rosenbluth plot. Though intrinsically small, of the order of a
few percent of the cross section, this correction is kinematically enhanced in
the Rosenbluth method while it is small for the polarization transfer method,
at least in the range of (Q^2) where it has been used until now.Comment: 4 pages, 4 figures. Version accepted for publication in Phys. Rev.
Let
Effective Field Theory and Unification in AdS Backgrounds
This work is an extension of our previous work, hep-th/0204160, which showed
how to systematically calculate the high energy evolution of gauge couplings in
compact AdS_5 backgrounds. We first directly compute the one-loop effects of
massive charged scalar fields on the low energy couplings of a gauge theory
propagating in the AdS background. It is found that scalar bulk mass scales
(which generically are of order the Planck scale) enter only logarithmically in
the corrections to the tree-level gauge couplings. As we pointed out
previously, we show that the large logarithms that appear in the AdS one-loop
calculation can be obtained within the confines of an effective field theory,
by running the Planck brane correlator from a high UV matching scale down to
the TeV scale. This result exactly reproduces our previous calculation, which
was based on AdS/CFT duality. We also calculate the effects of scalar fields
satisfying non-trivial boundary conditions (relevant for orbifold breaking of
bulk symmetries) on the running of gauge couplings.Comment: LaTeX, 27 pages; minor typos fixed, comments adde
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