15 research outputs found
Finite temperature phase transition for disordered weakly interacting bosons in one dimension
It is commonly accepted that there are no phase transitions in
one-dimensional (1D) systems at a finite temperature, because long-range
correlations are destroyed by thermal fluctuations. Here we demonstrate that
the 1D gas of short-range interacting bosons in the presence of disorder can
undergo a finite temperature phase transition between two distinct states:
fluid and insulator. None of these states has long-range spatial correlations,
but this is a true albeit non-conventional phase transition because transport
properties are singular at the transition point. In the fluid phase the mass
transport is possible, whereas in the insulator phase it is completely blocked
even at finite temperatures. We thus reveal how the interaction between
disordered bosons influences their Anderson localization. This key question,
first raised for electrons in solids, is now crucial for the studies of atomic
bosons where recent experiments have demonstrated Anderson localization in
expanding very dilute quasi-1D clouds.Comment: 8 pages, 5 figure
Reflecting diffusions and hyperbolic Brownian motions in multidimensional spheres
Diffusion processes moving inside
spheres and reflecting orthogonally on their
surfaces are considered. The stochastic differential equations
governing the reflecting diffusions are presented and their kernels and
distributions explicitly derived. Reflection is obtained by means of the
inversion with respect to the sphere . The particular cases of
Ornstein-Uhlenbeck process and Brownian motion are examined in detail.
The hyperbolic Brownian motion on the Poincar\`e half-space is
examined in the last part of the paper and its reflecting counterpart within
hyperbolic spheres is studied. Finally a section is devoted to reflecting
hyperbolic Brownian motion in the Poincar\`e disc within spheres concentric
with
Dynamics of localization in a waveguide
This is a review of the dynamics of wave propagation through a disordered
N-mode waveguide in the localized regime. The basic quantities considered are
the Wigner-Smith and single-mode delay times, plus the time-dependent power
spectrum of a reflected pulse. The long-time dynamics is dominated by resonant
transmission over length scales much larger than the localization length. The
corresponding distribution of the Wigner-Smith delay times is the Laguerre
ensemble of random-matrix theory. In the power spectrum the resonances show up
as a 1/t^2 tail after N^2 scattering times. In the distribution of single-mode
delay times the resonances introduce a dynamic coherent backscattering effect,
that provides a way to distinguish localization from absorption.Comment: 18 pages including 8 figures; minor correction
Searches for Gravitational Waves from Binary Neutron Stars: A Review
A new generation of observatories is looking for gravitational waves. These
waves, emitted by highly relativistic systems, will open a new window for ob-
servation of the cosmos when they are detected. Among the most promising
sources of gravitational waves for these observatories are compact binaries in
the final min- utes before coalescence. In this article, we review in brief
interferometric searches for gravitational waves emitted by neutron star
binaries, including the theory, instru- mentation and methods. No detections
have been made to date. However, the best direct observational limits on
coalescence rates have been set, and instrumentation and analysis methods
continue to be refined toward the ultimate goal of defining the new field of
gravitational wave astronomy.Comment: 30 pages, 5 Figures, to appear in "Short-Period Binary Stars:
Observations, Analyses, and Results", Ed.s Eugene F. Milone, Denis A. Leahy,
David W. Hobil
Gravitational-wave research as an emerging field in the Max Planck Society. The long roots of GEO600 and of the Albert Einstein Institute
On the occasion of the 50th anniversary since the beginning of the search for
gravitational waves at the Max Planck Society, and in coincidence with the 25th
anniversary of the foundation of the Albert Einstein Institute, we explore the
interplay between the renaissance of general relativity and the advent of
relativistic astrophysics following the German early involvement in
gravitational-wave research, to the point when gravitational-wave detection
became established by the appearance of full-scale detectors and international
collaborations. On the background of the spectacular astrophysical discoveries
of the 1960s and the growing role of relativistic astrophysics, Ludwig Biermann
and his collaborators at the Max Planck Institute for Astrophysics in Munich
became deeply involved in research related to such new horizons. At the end of
the 1960s, Joseph Weber's announcements claiming detection of gravitational
waves sparked the decisive entry of this group into the field, in parallel with
the appointment of the renowned relativist Juergen Ehlers. The Munich area
group of Max Planck institutes provided the fertile ground for acquiring a
leading position in the 1970s, facilitating the experimental transition from
resonant bars towards laser interferometry and its innovation at increasingly
large scales, eventually moving to a dedicated site in Hannover in the early
1990s. The Hannover group emphasized perfecting experimental systems at pilot
scales, and never developed a full-sized detector, rather joining the LIGO
Scientific Collaboration at the end of the century. In parallel, the Max Planck
Institute for Gravitational Physics (Albert Einstein Institute) had been
founded in Potsdam, and both sites, in Hannover and Potsdam, became a unified
entity in the early 2000s and were central contributors to the first detection
of gravitational waves in 2015.Comment: 94 pages. Enlarged version including new results from further
archival research. A previous version appears as a chapter in the volume The
Renaissance of General Relativity in Context, edited by A. Blum, R. Lalli and
J. Renn (Boston: Birkhauser, 2020