3,762 research outputs found
Bound States from Regge Trajectories in a Scalar Model
The calculation of bound state properties using renormalization group
techniques to compute the corresponding Regge trajectories is presented. In
particular, we investigate the bound states in different charge sectors of a
scalar theory with interaction (phi^dagger phi chi). The resulting bound state
spectrum is surprisingly rich. Where possible we compare and contrast with
known results of the Bethe-Salpeter equation in the ladder approximation and,
in the non-relativistic limit, with the corresponding Schr"odinger equation.Comment: 18 pages, 5 postscript figures, uses LaTeX2e with feynmf, amssymb and
psfi
Interaction of quasilocal harmonic modes and boson peak in glasses
The direct proportionality relation between the boson peak maximum in
glasses, , and the Ioffe-Regel crossover frequency for phonons,
, is established. For several investigated materials . At the frequency the mean free path of the
phonons becomes equal to their wavelength because of strong resonant
scattering on quasilocal harmonic oscillators. Above this frequency phonons
cease to exist. We prove that the established correlation between
and holds in the general case and is a direct consequence of
bilinear coupling of quasilocal oscillators with the strain field.Comment: RevTex, 4 pages, 1 figur
The information paradox and the locality bound
Hawking's argument for information loss in black hole evaporation rests on
the assumption of independent Hilbert spaces for the interior and exterior of a
black hole. We argue that such independence cannot be established without
incorporating strong gravitational effects that undermine locality and
invalidate the use of quantum field theory in a semiclassical background
geometry. These considerations should also play a role in a deeper
understanding of horizon complementarity.Comment: 21 pages, harvmac; v2-3. minor corrections, references adde
In Memoriam: Robert Irwin Cratty; John James Bushnell; Edward Jacob Petry; Winifred Gilbert; Ross W. Harris; Edward K. Putnam; Mary Louise Sawyer
Size Segregation of Granular Matter in Silo Discharges
We present an experimental study of segregation of granular matter in a
quasi-two dimensional silo emptying out of an orifice. Size separation is
observed when multi-sized particles are used with the larger particles found in
the center of the silo in the region of fastest flow. We use imaging to study
the flow inside the silo and quantitatively measure the concentration profiles
of bi-disperse beads as a function of position and time. The angle of the
surface is given by the angle of repose of the particles, and the flow occurs
in a few layers only near the top of this inclined surface. The flowing region
becomes deeper near the center of the silo and is confined to a parabolic
region centered at the orifice which is approximately described by the
kinematic model. The experimental evidence suggests that the segregation occurs
on the surface and not in the flow deep inside the silo where velocity
gradients also are present. We report the time development of the
concentrations of the bi-disperse particles as a function of size ratios, flow
rate, and the ratio of initial mixture. The qualitative aspects of the observed
phenomena may be explained by a void filling model of segregation.Comment: 6 pages, 10 figures (gif format), postscript version at
http://physics.clarku.edu/~akudrolli/nls.htm
Analog gravity from field theory normal modes?
We demonstrate that the emergence of a curved spacetime ``effective
Lorentzian geometry'' is a common and generic result of linearizing a field
theory around some non-trivial background. This investigation is motivated by
considering the large number of ``analog models'' of general relativity that
have recently been developed based on condensed matter physics, and asking
whether there is something more fundamental going on. Indeed, linearization of
a classical field theory (a field theoretic ``normal mode analysis'') results
in fluctuations whose propagation is governed by a Lorentzian-signature curved
spacetime ``effective metric''. For a single scalar field, this procedure
results in a unique effective metric, which is quite sufficient for simulating
kinematic aspects of general relativity (up to and including Hawking
radiation). Quantizing the linearized fluctuations, the one-loop effective
action contains a term proportional to the Einstein--Hilbert action, suggesting
that while classical physics is responsible for generating an ``effective
geometry'', quantum physics can be argued to induce an ``effective dynamics''.
The situation is strongly reminiscent of Sakharov's ``induced gravity''
scenario, and suggests that Einstein gravity is an emergent low-energy
long-distance phenomenon that is insensitive to the details of the high-energy
short-distance physics. (We mean this in the same sense that hydrodynamics is a
long-distance emergent phenomenon, many of whose predictions are insensitive to
the short-distance cutoff implicit in molecular dynamics.)Comment: Revtex 4 (beta 5); 12 pages in single-column forma
Black Hole Thermodynamics: Entropy, Information and Beyond
We review some recent advances in black hole thermodynamics, including
statistical mechanical origins of black hole entropy and its leading order
corrections, from the viewpoints of various quantum gravity theories. We then
examine the information loss problem and some possible approaches to its
resolution. Finally, we study some proposed experiments which may be able to
provide experimental signatures of black holes.Comment: Plenary talk given at the Fifth International Conference on
Gravitation and Cosmology, Cochin, 7 January 2004. 13 pages, Revte
The Cosmic-Ray Proton and Helium Spectra measured with the CAPRICE98 balloon experiment
A new measurement of the primary cosmic-ray proton and helium fluxes from 3
to 350 GeV was carried out by the balloon-borne CAPRICE experiment in 1998.
This experimental setup combines different detector techniques and has
excellent particle discrimination capabilities allowing clear particle
identification. Our experiment has the capability to determine accurately
detector selection efficiencies and systematic errors associated with them.
Furthermore, it can check for the first time the energy determined by the
magnet spectrometer by using the Cherenkov angle measured by the RICH detector
well above 20 GeV/n. The analysis of the primary proton and helium components
is described here and the results are compared with other recent measurements
using other magnet spectrometers. The observed energy spectra at the top of the
atmosphere can be represented by (1.27+-0.09)x10^4 E^(-2.75+-0.02) particles
(m^2 GeV sr s)^-1, where E is the kinetic energy, for protons between 20 and
350 GeV and (4.8+-0.8)x10^2 E^(-2.67+-0.06) particles (m^2 GeV nucleon^-1 sr
s)^-1, where E is the kinetic energy per nucleon, for helium nuclei between 15
and 150 GeV nucleon^-1.Comment: To be published on Astroparticle Physics (44 pages, 13 figures, 5
tables
WLM-1: A Non-Rotating, Gravitationally Unperturbed, Highly Elliptical Extragalactic Globular Cluster
Globular clusters have long been known for presenting (at times) significant
deviations from spherical symmetry. While rotation has been the main proposed
explanation, other complicating factors such as their constant interaction with
the strong gravitational potential of their host galaxy have made it difficult
for a consensus to be reached. To address this question we have obtained
high-resolution spectra of WLM-1, the lone globular cluster associated with the
isolated, low-mass dwarf irregular galaxy WLM. Using archival HST WFPC2 data,
we measure the radial ellipticity profile of WLM-1, finding it to be highly
elliptical, with a mean value of 0.17 in the region 0.5-5" -- which is
comparable to what is found in our Galaxy for the most elliptical globular
clusters. There is no evidence of isophote twisting, except for the innermost
regions of the cluster (r < 0.5"). To investigate whether the observed
flattening can be ascribed to rotation, we have obtained long-slit
high-resolution VLT/UVES spectra of this cluster along and perpendicular to the
axis of flattening. Using cross-correlation we find that the velocity profile
of the cluster is consistent with zero rotation along either axis. Thus neither
cluster rotation nor galactic tides can be responsible for the flattened
morphology of WLM-1. We argue that the required velocity dispersion anisotropy
between the semi-major and semi-minor axes that would be required to account
for the observed flattening is relatively small, of order 1 km/s. Even though
our errors preclude us from conclusively establishing that such a difference
indeed exists, velocity anisotropy remains at present the most plausible
explanation for the shape of this cluster.Comment: 11 pages, 10 figures, submitted to the A
Low-temperature specific heat and thermal conductivity of glycerol
We have measured the thermal conductivity of glassy glycerol between 1.5 K
and 100 K, as well as the specific heat of both glassy and crystalline phases
of glycerol between 0.5 K and 25 K. We discuss both low-temperature properties
of this typical molecular glass in terms of the soft-potential model. Our
finding of an excellent agreement between its predictions and experimental data
for these two independent measurements constitutes a robust proof of the
capabilities of the soft-potential model to account for the low-temperature
properties of glasses in a wide temperature range.Comment: 4 pages, 3 figures. To be published in Phys. Rev. B (2002
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