4,340 research outputs found
Black Holes at the IceCube Neutrino Telescope
If the fundamental Planck scale is about a TeV and the cosmic neutrino flux
is at the Waxman-Bahcall level, quantum black holes are created daily in the
Antarctic ice-cap. We re-examine the prospects for observing such black holes
with the IceCube neutrino-detection experiment. To this end, we first revise
the black hole production rate by incorporating the effects of inelasticty,
i.e., the energy radiated in gravitational waves by the multipole moments of
the incoming shock waves. After that we study in detail the process of Hawking
evaporation accounting for the black hole's large momentum in the lab system.
We derive the energy spectrum of the Planckian cloud which is swept forward
with a large, O (10^6), Lorentz factor. (It is noteworthy that the boosted
thermal spectrum is also relevant for the study of near-extremal supersymmetric
black holes, which could be copiously produced at the LHC.) In the
semiclassical regime, we estimate the average energy of the boosted particles
to be less than 20% the energy of the neutrino-progenitor. Armed with such a
constraint, we determine the discovery reach of IceCube by tagging on "soft"
(relative to what one would expect from charged current standard model
processes) muons escaping the electromagnetic shower bubble produced by the
black hole's light descendants. The statistically significant 5-sigma excess
extends up to a quantum gravity scale ~ 1.3 TeV.Comment: Matching version to be published in Phys. Rev.
From AMANDA to IceCube
The first string of the neoteric high energy neutrino telescope IceCube
successfully began operating in January 2005. It is anticipated that upon
completion the new detector will vastly increase the sensitivity and extend the
reach of AMANDA to higher energies. A discussion of the IceCube's discovery
potential for extra-terrestrial neutrinos, together with the prospects of new
physics derived from the ongoing AMANDA research will be the focus of this
paper. Preliminary results of the first antarctic high energy neutrino
telescope AMANDA searching in the muon neutrino channel for localized and
diffuse excess of extra-terrestrial neutrinos will be reviewed using data
collected between 2000 and 2003. Neutrino flux limits obtained with the
all-flavor dedicated UHE and cascade analyses will be described. A first
neutrino spectrum above one TeV in agreement with atmospheric neutrino flux
expectations and no extra-terrestrial contribution will be presented, followed
by a discussion of a limit for neutralino CDM candidates annihilating in the
center of the Sun.Comment: 15 pages, 8 figures Invited talk contribution at 5th International
Conference on Non-accelerator New Physics (NANP 05), Dubna, Russia, 20-25 Jun
200
Photoproduction of eta-mesic 3He
The photoproduction of eta-mesic 3He has been investigated using the TAPS
calorimeter at the Mainz Microtron accelerator facility MAMI. The total
inclusive cross section for the reaction gamma+3He->eta+X has been measured for
photon energies from threshold to 820 MeV. The total and angular differential
coherent eta cross sections have been extracted up to energies of 745 MeV. A
resonance-like structure just above the eta production threshold with an
isotropic angular distribution suggests the existence of a resonant quasi-bound
state. This is supported by studies of a competing decay channel of such a
quasi-bound eta-mesic nucleus into pi^0+p+X. A binding energy of (-4.4+-4.2)
MeV and a width of (25.6+-6.1) MeV is deduced for the quasi-bound eta-mesic
state in 3He.Comment: v1: 4 pages, 4 figures, submitted to PRL; v2: minor revisions and
corrections, new figure added, 4 pages, 5 figs; v3: minor change
Full abstraction for fair testing in CCS
In previous work with Pous, we defined a semantics for CCS which may both be
viewed as an innocent presheaf semantics and as a concurrent game semantics. It
is here proved that a behavioural equivalence induced by this semantics on CCS
processes is fully abstract for fair testing equivalence. The proof relies on a
new algebraic notion called playground, which represents the 'rule of the
game'. From any playground, two languages, equipped with labelled transition
systems, are derived, as well as a strong, functional bisimulation between
them.Comment: 15 pages, to appear in CALCO '13. To appear Lecture notes in computer
science (2013
The reaction and the magnetic dipole moment of the resonance
The reaction has been measured with
the TAPS calorimeter at the Mainz Microtron accelerator facility MAMI for
energies between = 1221--1331 MeV. Cross sections differential in
angle and energy have been determined for all particles in the final state in
three bins of the excitation energy. This reaction channel provides access to
the magnetic dipole moment of the resonance and, for the
first time, a value of has been extracted
Self-Consistent Field study of Polyelectrolyte Brushes
We formulate a self-consistent field theory for polyelectrolyte brushes in
the presence of counterions. We numerically solve the self-consistent field
equations and study the monomer density profile, the distribution of
counterions, and the total charge distribution. We study the scaling relations
for the brush height and compare them to the prediction of other theories. We
find a weak dependence of the brush height on the grafting density.We fit the
counterion distribution outside the brush by the Gouy-Chapman solution for a
virtual charged wall. We calculate the amount of counterions outside the brush
and find that it saturates as the charge of the polyelectrolytes increases
A model for MRI contrast enhancement using T_1 agents
Contrast in MRI relies on differences in the local environment of water and is often enhanced by using contrast agents. We present a simple model for evaluating the minimal contrast agent concentration required to produce “satisfactory” contrast enhancement in magnetic resonance images. Previous strategies have been based largely on empirical results for specific systems. The present tissue contrast model (TCM) can be applied to “conventional,” targeted, or biochemically responsive agents. The model results are formulated so that only a small number of parameters are required to analyze a given scenario. The TCM is a particularly useful tool in the development of new classes of magnetic resonance contrast media. These agents will have the ability to target specific cells or tissue, and perhaps be able to report on their physiological status. As an example of the applicability of the TCM, we test it against in vivo magnetic resonance microscopy results in frog embryos that have focal cell populations labeled with contrast agent by using calibrated single-cell microinjection techniques
RG-improved single-particle inclusive cross sections and forward-backward asymmetry in production at hadron colliders
We use techniques from soft-collinear effective theory (SCET) to derive
renormalization-group improved predictions for single-particle inclusive (1PI)
observables in top-quark pair production at hadron colliders. In particular, we
study the top-quark transverse-momentum and rapidity distributions, the
forward-backward asymmetry at the Tevatron, and the total cross section at
NLO+NNLL order in resummed perturbation theory and at approximate NNLO in fixed
order. We also perform a detailed analysis of power corrections to the leading
terms in the threshold expansion of the partonic hard-scattering kernels. We
conclude that, although the threshold expansion in 1PI kinematics is
susceptible to numerically significant power corrections, its predictions for
the total cross section are in good agreement with those obtained by
integrating the top-pair invariant-mass distribution in pair invariant-mass
kinematics, as long as a certain set of subleading terms appearing naturally
within the SCET formalism is included.Comment: 55 pages, 14 figures, 6 table
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