8,819 research outputs found
Exploiting the directional sensitivity of the Double Chooz near detector
In scintillator detectors, the forward displacement of the neutron in the
reaction provides neutrino directional information as
demonstrated by the CHOOZ reactor experiment with 2,500 events. The near
detector of the forthcoming Double Chooz experiment will collect
events per year, enough to determine the average neutrino
direction with a half-cone aperture of in one year. It
is more difficult to separate the two Chooz reactors that are viewed at a
separation angle . If their strengths are known and
approximately equal, the azimuthal location of each reactor is obtained with
() and the probability of confusing them with a single
source is less than 11%. Five year's data reduce this ``confusion probability''
to less than 0.3%, i.e., a separation is possible. All of these
numbers improve rapidly with increasing angular separation of the sources. For
a setup with and one year's data, the azimuthal
uncertainty for each source decreases to . Of course, for Double
Chooz the two reactor locations are known, allowing one instead to measure
their individual one-year integrated power output to (), and
their five-year integrated output to ().Comment: 7 pages, 10 figure
Affinity Labelling of the Active Center of DNA-dependent RNA Polymerases within the Archaebacterial Kingdom
Signatures of axion-like particles in the spectra of TeV gamma-ray sources
One interpretation of the unexplained signature observed in the PVLAS
experiment invokes a new axion-like particle (ALP) with a two-photon vertex,
allowing for photon-ALP oscillations in the presence of magnetic fields. In the
range of masses and couplings suggested by PVLAS, the same effect would lead to
a peculiar dimming of high-energy photon sources. For typical parameters of the
turbulent magnetic field in the galaxy, the effect sets in at E_gamma >~ 10
TeV, providing an ALP signature in the spectra of TeV gamma sources that can be
probed with Cherenkov telescopes. A dedicated search will be strongly motivated
if the ongoing photon regeneration experiments confirm the PVLAS particle
interpretation.Comment: 8 pages, 1 eps figure; typos corrected, matches published versio
A Formalism for Scattering of Complex Composite Structures. 1 Applications to Branched Structures of Asymmetric Sub-Units
We present a formalism for the scattering of an arbitrary linear or acyclic
branched structure build by joining mutually non-interacting arbitrary
functional sub-units. The formalism consists of three equations expressing the
structural scattering in terms of three equations expressing the sub-unit
scattering. The structural scattering expressions allows a composite structures
to be used as sub-units within the formalism itself. This allows the scattering
expressions for complex hierarchical structures to be derived with great ease.
The formalism is furthermore generic in the sense that the scattering due to
structural connectivity is completely decoupled from internal structure of the
sub-units. This allows sub-units to be replaced by more complex structures. We
illustrate the physical interpretation of the formalism diagrammatically. By
applying a self-consistency requirement we derive the pair distributions of an
ideal flexible polymer sub-unit. We illustrate the formalism by deriving
generic scattering expressions for branched structures such as stars, pom-poms,
bottle-brushes, and dendrimers build out of asymmetric two-functional
sub-units.Comment: Complete rewrite generalizing the formalism to arbitrary functional
sub-units and including a new Feynmann like diagrammatic interpretatio
A Formalism for Scattering of Complex Composite Structures. 2 Distributed Reference Points
Recently we developed a formalism for the scattering from linear and acyclic
branched structures build of mutually non-interacting sub-units.{[}C. Svaneborg
and J. S. Pedersen, J. Chem. Phys. 136, 104105 (2012){]} We assumed each
sub-unit has reference points associated with it. These are well defined
positions where sub-units can be linked together. In the present paper, we
generalize the formalism to the case where each reference point can represent a
distribution of potential link positions. We also present a generalized
diagrammatic representation of the formalism. Scattering expressions required
to model rods, polymers, loops, flat circular disks, rigid spheres and
cylinders are derived. and we use them to illustrate the formalism by deriving
the generic scattering expression for micelles and bottle brush structures and
show how the scattering is affected by different choices of potential link
positions.Comment: Paper no. 2 of a serie
Systematic approach to leptogenesis in nonequilibrium QFT: vertex contribution to the CP-violating parameter
The generation of a baryon asymmetry via leptogenesis is usually studied by
means of classical kinetic equations whose applicability to processes in the
hot and expanding early universe is questionable. The approximations implied by
the state-of-the-art description can be tested in a first-principle approach
based on nonequilibrium field theory techniques. Here, we apply the
Schwinger-Keldysh/Kadanoff-Baym formalism to a simple toy model of
leptogenesis. We find that, within the toy model, medium effects increase the
vertex contribution to the CP-violating parameter. At high temperatures it is a
few times larger than in vacuum and asymptotically reaches the vacuum value as
the temperature decreases. Contrary to the results obtained earlier in the
framework of thermal field theory, the corrections are only linear in the
particle number densities. An important feature of the Kadanoff-Baym formalism
is that it is free of the double-counting problem, i.e. no need for real
intermediate state subtraction arises. In particular, this means that the
structure of the equations automatically ensures that the asymmetry vanishes in
equilibrium. These results give a first glimpse into a number of new and
interesting effects that can be studied in the framework of nonequilibrium
field theory.Comment: 27 pages, 21 figure
Vortex Dynamics and Hall Conductivity of Hard Core Bosons
Magneto-transport of hard core bosons (HCB) is studied using an XXZ quantum
spin model representation, appropriately gauged on the torus to allow for an
external magnetic field. We find strong lattice effects near half filling. An
effective quantum mechanical description of the vortex degrees of freedom is
derived. Using semiclassical and numerical analysis we compute the vortex
hopping energy, which at half filling is close to magnitude of the boson
hopping energy. The critical quantum melting density of the vortex lattice is
estimated at 6.5x10-5 vortices per unit cell. The Hall conductance is computed
from the Chern numbers of the low energy eigenstates. At zero temperature, it
reverses sign abruptly at half filling. At precisely half filling, all
eigenstates are doubly degenerate for any odd number of flux quanta. We prove
the exact degeneracies on the torus by constructing an SU(2) algebra of
point-group symmetries, associated with the center of vorticity. This result is
interpreted as if each vortex carries an internal spin-half degree of freedom
('vspin'), which can manifest itself as a charge density modulation in its
core. Our findings suggest interesting experimental implications for vortex
motion of cold atoms in optical lattices, and magnet-transport of short
coherence length superconductors.Comment: 15 pages, 15 figure
Neutrino Physics: Open Theoretical Questions
We know that neutrino mass and mixing provide a window to physics beyond the
Standard Model. Now this window is open, at least partly. And the questions
are: what do we see, which kind of new physics, and how far "beyond"? I
summarize the present knowledge of neutrino mass and mixing, and then formulate
the main open questions. Following the bottom-up approach, properties of the
neutrino mass matrix are considered. Then different possible ways to uncover
the underlying physics are discussed. Some results along the line of: see-saw,
GUT and SUSY GUT are reviewed.Comment: 17 pages, latex, 12 figures. Talk given at the XXI International
Symposium on Lepton and Photon Interactions at High Energies, ``Lepton Photon
2003", August 11-16, 2003 - Fermilab, Batavia, IL US
- …