39,913 research outputs found
Neutrinos from active black holes, sources of ultra high energy cosmic rays
A correlation between the highest energy Cosmic Rays (above ~ EeV) and the
distribution of active galactic nuclei (AGN) gives rise to a prediction of
neutrino production in the same sources. In this paper, we present a detailed
AGN model, predicting neutrino production near the foot of the jet, where the
photon fields from the disk and synchrotron radiation from the jet itself
create high optical depths for proton-photon interactions. The protons escape
from later shocks where the emission region is optically thin for proton-photon
interactions. Consequently, Cosmic Rays are predicted to come from FR-I
galaxies, independent of the orientation of the source. Neutrinos, on the other
hand, are only observable from sources directing their jet towards Earth, i.e.
flat spectrum radio sources and in particular BL Lac type objects, due to the
strongly boosted neutrino emission.Comment: Accepted for publication in Astroparticle Physics; 30 pages, 8
figure
The diffuse neutrino flux from FR-II radio galaxies and blazars: A source property based estimate
Water and ice Cherenkov telescopes of the present and future aim for the
detection of a neutrino signal from extraterrestrial sources at energies E>PeV.
Some of the most promising extragalactic sources are Active Galactic Nuclei
(AGN). In this paper, the neutrino flux from two kinds of AGN sources will be
estimated assuming photohadronic interactions in the jet of the AGN. The first
analyzed sample contains FR-II radio galaxies while the second AGN type
examined are blazars. The result is highly dependent on the proton's index of
the energy spectrum. To normalize the spectrum, the connection between neutrino
and disk luminosity will be used by applying the jet-disk symbiosis model from
Falcke and Biermann (1995). The maximum proton energy and thus, also the
maximum neutrino energy of the source is connected to its disk luminosity,
which was shown by Lovelace (1976) and was confirmed by Falcke et al. (1995).Comment: 24 pages, 14 figures, to be published in Astroparticle Physic
Neutrinos from photo-hadronic interactions in Pks2155-304
The high-peaked BL Lac object Pks2155-304 shows high variability at
multiwavelengths, i.e. from optical up to TeV energies. A giant flare of around
1 hour at X-ray and TeV energies was observed in 2006. In this context, it is
essential to understand the physical processes in terms of the primary spectrum
and the radiation emitted, since high-energy emission can arise in both
leptonic and hadronic processes. In this contribution, we investigate the
possibility of neutrino production in photo-hadronic interactions. In
particular, we predict a direct correlation between optical and TeV energies at
sufficiently high optical radiation fields. We show that in the blazar
Pks2155-304, the optical emission in the low-state is sufficient to lead to
photo-hadronic interactions and therefore to the production of high-energy
photons.Comment: contribution to RICAP 2009 and ICRC 2009 - both papers are combined
in one draft. 11 pages, 3 figure
String vacua with flux from freely-acting obifolds
A precise correspondence between freely-acting orbifolds (Scherk-Schwarz
compactifications) and string vacua with NSNS flux turned on is established
using T-duality.
We focus our attention to a certain non-compact Z_2 heterotic freely-acting
orbifold with N=2 supersymmetry (SUSY). The geometric properties of the T-dual
background are studied. As expected, the space is non-Kahler with the most
generic torsion compatible with SUSY. All equations of motion are satisfied,
except the Bianchi identity for the NSNS field, that is satisfied only at
leading order in derivatives, i.e. without the curvature term. We point out
that this is due to unknown corrections to the standard heterotic T-duality
rules.Comment: 13 pages, no figures; v2: references added and rearranged, version to
appear in JHE
Integral field spectroscopy of QSO host galaxies
We describe a project to study the state of the ISM in ~20 low redshift
(z<0.3) QSO host galaxies observed with the PMAS integral field spectrograph.
We describe method developement to access the stellar and gas component of the
spectrum without the strong nuclear emission to access the host galaxy
properties also in the central region. It shows that integral field
spectroscopy promises to be very efficient to study the gas distribution and
its velocity field, and also spatially resolved stellar population in the host
galaxies also of luminous AGN.Comment: 4 pages, 6 figures, Euro3D Science Workshop, Cambridge, May 2003, AN,
accepte
Ultracold quantum gases in triangular optical lattices
Over the last years the exciting developments in the field of ultracold atoms
confined in optical lattices have led to numerous theoretical proposals devoted
to the quantum simulation of problems e.g. known from condensed matter physics.
Many of those ideas demand for experimental environments with non-cubic lattice
geometries. In this paper we report on the implementation of a versatile
three-beam lattice allowing for the generation of triangular as well as
hexagonal optical lattices. As an important step the superfluid-Mott insulator
(SF-MI) quantum phase transition has been observed and investigated in detail
in this lattice geometry for the first time. In addition to this we study the
physics of spinor Bose-Einstein condensates (BEC) in the presence of the
triangular optical lattice potential, especially spin changing dynamics across
the SF-MI transition. Our results suggest that below the SF-MI phase
transition, a well-established mean-field model describes the observed data
when renormalizing the spin-dependent interaction. Interestingly this opens new
perspectives for a lattice driven tuning of a spin dynamics resonance occurring
through the interplay of quadratic Zeeman effect and spin-dependent
interaction. We finally discuss further lattice configurations which can be
realized with our setup.Comment: 19 pages, 7 figure
Relativistic linear stability equations for the nonlinear Dirac equation in Bose-Einstein condensates
We present relativistic linear stability equations (RLSE) for
quasi-relativistic cold atoms in a honeycomb optical lattice. These equations
are derived from first principles and provide a method for computing
stabilities of arbitrary localized solutions of the nonlinear Dirac equation
(NLDE), a relativistic generalization of the nonlinear Schr\"odinger equation.
We present a variety of such localized solutions: skyrmions, solitons,
vortices, and half-quantum vortices, and study their stabilities via the RLSE.
When applied to a uniform background, our calculations reveal an experimentally
observable effect in the form of Cherenkov radiation. Remarkably, the Berry
phase from the bipartite structure of the honeycomb lattice induces a
boson-fermion transmutation in the quasi-particle operator statistics.Comment: 6 pages, 3 figure
Interference effects in above-threshold ionization from diatomic molecules: determining the internuclear separation
We calculate angle-resolved above-threshold ionization spectra for diatomic
molecules in linearly polarized laser fields, employing the strong-field
approximation. The interference structure resulting from the individual
contributions of the different scattering scenarios is discussed in detail,
with respect to the dependence on the internuclear distance and molecular
orientation. We show that, in general, the contributions from the processes in
which the electron is freed at one center and rescatters off the other obscure
the interference maxima and minima obtained from single-center processes.
However, around the boundary of the energy regions for which rescattering has a
classical counterpart, such processes play a negligible role and very clear
interference patterns are observed. In such energy regions, one is able to
infer the internuclear distance from the energy difference between adjacent
interference minima.Comment: 10 pages, 8 figures; discussions slightly modified and an additional
figure inserted for clarit
Linear Sigma Models with Torsion
Gauged linear sigma models with (0,2) supersymmetry allow a larger choice of
couplings than models with (2,2) supersymmetry. We use this freedom to find a
fully linear construction of torsional heterotic compactifications, including
models with branes. As a non-compact example, we describe a family of metrics
which correspond to deformations of the heterotic conifold by turning on
H-flux. We then describe compact models which are gauge-invariant only at the
quantum level. Our construction gives a generalization of symplectic reduction.
The resulting spaces are non-Kahler analogues of familiar toric spaces like
complex projective space. Perturbatively conformal models can be constructed by
considering intersections.Comment: 40 pages, LaTeX, 1 figure; references added; a new section on
supersymmetry added; quantization condition revisite
Status of neutrino astronomy
Astrophysical neutrinos can be produced in proton interactions of charged
cosmic rays with ambient photon or baryonic fields. Cosmic rays are observed in
balloon, satellite and air shower experiments every day, from below 1e9 eV up
to macroscopic energies of 1e21 eV. The observation of different photon fields
has been done ever since, today with detections ranging from radio wavelengths
up to very high-energy photons in the TeV range. The leading question for
neutrino astronomers is now which sources provide a combination of efficient
proton acceleration with sufficiently high photon fields or baryonic targets at
the same time in order to produce a neutrino flux that is high enough to exceed
the background of atmospheric neutrinos. There are only two confirmed
astrophysical neutrino sources up to today: the sun and SuperNova 1987A emit
and emitted neutrinos at MeV energies. The aim of large underground Cherenkov
telescopes like IceCube and KM3NeT is the detection of neutrinos at energies
above 100 GeV. In this paper, recent developments of neutrino flux modeling for
the most promising extragalactic sources, gamma ray bursts and active galactic
nuclei, are presented.Comment: Talk given at Neutrino 2008, Christchurch (New Zealand) 6 pages, 4
figures, 1 tabl
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