340 research outputs found
Super-Radiant Dynamics, Doorways, and Resonances in Nuclei and Other Open Mesoscopic Systems
The phenomenon of super-radiance (Dicke effect, coherent spontaneous
radiation by a gas of atoms coupled through the common radiation field) is well
known in quantum optics. The review discusses similar physics that emerges in
open and marginally stable quantum many-body systems. In the presence of open
decay channels, the intrinsic states are coupled through the continuum. At
sufficiently strong continuum coupling, the spectrum of resonances undergoes
the restructuring with segregation of very broad super-radiant states and
trapping of remaining long-lived compound states. The appropriate formalism
describing this phenomenon is based on the Feshbach projection method and
effective non-Hermitian Hamiltonian. A broader generalization is related to the
idea of doorway states connecting quantum states of different structure. The
method is explained in detail and the examples of applications are given to
nuclear, atomic and particle physics. The interrelation of the collective
dynamics through continuum and possible intrinsic many-body chaos is studied,
including universal mesoscopic conductance fluctuations. The theory serves as a
natural framework for general description of a quantum signal transmission
through an open mesoscopic system.Comment: 85 pages, 10 figure
The Alexander-Orbach conjecture holds in high dimensions
We examine the incipient infinite cluster (IIC) of critical percolation in
regimes where mean-field behavior has been established, namely when the
dimension d is large enough or when d>6 and the lattice is sufficiently spread
out. We find that random walk on the IIC exhibits anomalous diffusion with the
spectral dimension d_s=4/3, that is, p_t(x,x)= t^{-2/3+o(1)}. This establishes
a conjecture of Alexander and Orbach. En route we calculate the one-arm
exponent with respect to the intrinsic distance.Comment: 25 pages, 2 figures. To appear in Inventiones Mathematica
Muon-induced background in the EDELWEISS dark matter search
A dedicated analysis of the muon-induced background in the EDELWEISS dark
matter search has been performed on a data set acquired in 2009 and 2010. The
total muon flux underground in the Laboratoire Souterrain de Modane (LSM) was
measured to be \,muons/m/d. The
modular design of the muon-veto system allows the reconstruction of the muon
trajectory and hence the determination of the angular dependent muon flux in
LSM. The results are in good agreement with both MC simulations and earlier
measurements. Synchronization of the muon-veto system with the phonon and
ionization signals of the Ge detector array allowed identification of
muon-induced events. Rates for all muon-induced events and of WIMP-like events were extracted. After
vetoing, the remaining rate of accepted muon-induced neutrons in the
EDELWEISS-II dark matter search was determined to be at 90%\,C.L. Based on
these results, the muon-induced background expectation for an anticipated
exposure of 3000\,\kgd\ for EDELWEISS-3 is
events.Comment: 21 pages, 16 figures, Accepted for publication in Astropart. Phy
Axion searches with the EDELWEISS-II experiment
We present new constraints on the couplings of axions and more generic
axion-like particles using data from the EDELWEISS-II experiment. The EDELWEISS
experiment, located at the Underground Laboratory of Modane, primarily aims at
the direct detection of WIMPs using germanium bolometers. It is also sensitive
to the low-energy electron recoils that would be induced by solar or dark
matter axions. Using a total exposure of up to 448 kg.d, we searched for
axion-induced electron recoils down to 2.5 keV within four scenarios involving
different hypotheses on the origin and couplings of axions. We set a 95% CL
limit on the coupling to photons GeV in
a mass range not fully covered by axion helioscopes. We also constrain the
coupling to electrons, , similar to the more
indirect solar neutrino bound. Finally we place a limit on , where is the
effective axion-nucleon coupling for Fe. Combining these results we
fully exclude the mass range keV for DFSZ axions and
keV for KSVZ axions
Highlights from the Pierre Auger Observatory
The Pierre Auger Observatory is the world's largest cosmic ray observatory.
Our current exposure reaches nearly 40,000 km str and provides us with an
unprecedented quality data set. The performance and stability of the detectors
and their enhancements are described. Data analyses have led to a number of
major breakthroughs. Among these we discuss the energy spectrum and the
searches for large-scale anisotropies. We present analyses of our X
data and show how it can be interpreted in terms of mass composition. We also
describe some new analyses that extract mass sensitive parameters from the 100%
duty cycle SD data. A coherent interpretation of all these recent results opens
new directions. The consequences regarding the cosmic ray composition and the
properties of UHECR sources are briefly discussed.Comment: 9 pages, 12 figures, talk given at the 33rd International Cosmic Ray
Conference, Rio de Janeiro 201
A search for point sources of EeV photons
Measurements of air showers made using the hybrid technique developed with
the fluorescence and surface detectors of the Pierre Auger Observatory allow a
sensitive search for point sources of EeV photons anywhere in the exposed sky.
A multivariate analysis reduces the background of hadronic cosmic rays. The
search is sensitive to a declination band from -85{\deg} to +20{\deg}, in an
energy range from 10^17.3 eV to 10^18.5 eV. No photon point source has been
detected. An upper limit on the photon flux has been derived for every
direction. The mean value of the energy flux limit that results from this,
assuming a photon spectral index of -2, is 0.06 eV cm^-2 s^-1, and no celestial
direction exceeds 0.25 eV cm^-2 s^-1. These upper limits constrain scenarios in
which EeV cosmic ray protons are emitted by non-transient sources in the
Galaxy.Comment: 28 pages, 10 figures, accepted for publication in The Astrophysical
Journa
Reconstruction of inclined air showers detected with the Pierre Auger Observatory
We describe the method devised to reconstruct inclined cosmic-ray air showers
with zenith angles greater than detected with the surface array of
the Pierre Auger Observatory. The measured signals at the ground level are
fitted to muon density distributions predicted with atmospheric cascade models
to obtain the relative shower size as an overall normalization parameter. The
method is evaluated using simulated showers to test its performance. The energy
of the cosmic rays is calibrated using a sub-sample of events reconstructed
with both the fluorescence and surface array techniques. The reconstruction
method described here provides the basis of complementary analyses including an
independent measurement of the energy spectrum of ultra-high energy cosmic rays
using very inclined events collected by the Pierre Auger Observatory.Comment: 27 pages, 19 figures, accepted for publication in Journal of
Cosmology and Astroparticle Physics (JCAP
The Pierre Auger Observatory III: Other Astrophysical Observations
Astrophysical observations of ultra-high-energy cosmic rays with the Pierre
Auger ObservatoryComment: Contributions to the 32nd International Cosmic Ray Conference,
Beijing, China, August 201
Operations of and Future Plans for the Pierre Auger Observatory
Technical reports on operations and features of the Pierre Auger Observatory,
including ongoing and planned enhancements and the status of the future
northern hemisphere portion of the Observatory. Contributions to the 31st
International Cosmic Ray Conference, Lodz, Poland, July 2009.Comment: Contributions to the 31st ICRC, Lodz, Poland, July 200
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