10,616 research outputs found
Proton decay matrix elements with domain-wall fermions
Hadronic matrix elements of operators relevant to nucleon decay in grand
unified theories are calculated numerically using lattice QCD. In this context,
the domain-wall fermion formulation, combined with non-perturbative
renormalization, is used for the first time. These techniques bring reduction
of a large fraction of the systematic error from the finite lattice spacing.
Our main effort is devoted to a calculation performed in the quenched
approximation, where the direct calculation of the nucleon to pseudoscalar
matrix elements, as well as the indirect estimate of them from the nucleon to
vacuum matrix elements, are performed. First results, using two flavors of
dynamical domain-wall quarks for the nucleon to vacuum matrix elements are also
presented to address the systematic error of quenching, which appears to be
small compared to the other errors. Our results suggest that the representative
value for the low energy constants from the nucleon to vacuum matrix elements
are given as |alpha| simeq |beta| simeq 0.01 GeV^3. For a more reliable
estimate of the physical low energy matrix elements, it is better to use the
relevant form factors calculated in the direct method. The direct method tends
to give smaller value of the form factors, compared to the indirect one, thus
enhancing the proton life-time; indeed for the pi^0 final state the difference
between the two methods is quite appreciable.Comment: 56 pages, 17 figures, a comment and two references added in the
introduction, typo corrected in Eq.1
Simulation Study of TenTen: A new Multi-TeV IACT array
TenTen is a proposed array of Imaging Atmospheric Cherenkov Telescopes (IACT)
optimized for the gamma ray energy regime of 10 TeV to 100 TeV, but with a
threshold of ~1 to a few TeV. It will offer a collecting area of 10 km2 above
energies of 10 TeV. In the initial phase, a cell of 3 to 5 modest-sized
telescopes, each with 10-30 m2 mirror area, is suggested for an Australian
site. A possible expansion of the array could comprise many such cells. Here we
present work on configuration and technical issues from our simulation studies
of the array. Working topics include array layout, telescope size and optics,
camera field of view, telescope trigger system, electronics, and site surveys.Comment: 4 pages, 7 figures, submitted to Proceedings of the ICRC 2007, pdf
forma
TenTen: A New Array of Multi-TeV Imaging Cherenkov Telescopes
The exciting results from H.E.S.S. point to a new population of gamma-ray
sources at energies E > 10 TeV, paving the way for future studies and new
discoveries in the multi-TeV energy range. Connected with these energies is the
search for sources of PeV cosmic-rays (CRs) and the study of multi-TeV
gamma-ray production in a growing number of astrophysical environments. TenTen
is a proposed stereoscopic array (with a suggested site in Australia) of
modest-sized (10 to 30m^2) Cherenkov imaging telescopes with a wide field of
view (8 to 10deg diameter) optimised for the E~10 to 100 TeV range. TenTen will
achieve an effective area of ~10 km^2 at energies above 10 TeV. We outline here
the motivation for TenTen and summarise key performance parameters.Comment: 4 pages, 2 figures, proceedings of the 30th ICRC, Merida, Mexico,
200
On the forward cone quantization of the Dirac field in "longitudinal boost-invariant" coordinates with cylindrical symmetry
We obtain a complete set of free-field solutions of the Dirac equation in a
(longitudinal) boost-invariant geometry with azimuthal symmetry and use these
solutions to perform the canonical quantization of a free Dirac field of mass
. This coordinate system which uses the 1+1 dimensional fluid rapidity and the fluid proper time is
relevant for understanding particle production of quarks and antiquarks
following an ultrarelativistic collision of heavy ions, as it incorporates the
(approximate) longitudinal "boost invariance" of the distribution of outgoing
particles. We compare two approaches to solving the Dirac equation in
curvilinear coordinates, one directly using Vierbeins, and one using a
"diagonal" Vierbein representation
Immediate effects of diamond burr debridement in patients with spontaneous chronic corneal epithelial defects, light and electron microscopic evaluation
Timing analysis techniques at large core distances for multi-TeV gamma ray astronomy
We present an analysis technique that uses the timing information of
Cherenkov images from extensive air showers (EAS). Our emphasis is on distant,
or large core distance gamma-ray induced showers at multi-TeV energies.
Specifically, combining pixel timing information with an improved direction
reconstruction algorithm, leads to improvements in angular and core resolution
as large as ~40% and ~30%, respectively, when compared with the same algorithm
without the use of timing. Above 10 TeV, this results in an angular resolution
approaching 0.05 degrees, together with a core resolution better than ~15 m.
The off-axis post-cut gamma-ray acceptance is energy dependent and its full
width at half maximum ranges from 4 degrees to 8 degrees. For shower directions
that are up to ~6 degrees off-axis, the angular resolution achieved by using
timing information is comparable, around 100 TeV, to the on-axis angular
resolution. The telescope specifications and layout we describe here are geared
towards energies above 10 TeV. However, the methods can in principle be applied
to other energies, given suitable telescope parameters. The 5-telescope cell
investigated in this study could initially pave the way for a larger array of
sparsely spaced telescopes in an effort to push the collection area to >10 km2.
These results highlight the potential of a `sparse array' approach in
effectively opening up the energy range above 10 TeV.Comment: Published in Astroparticle Physic
Three Dimensional Relativistic Electromagnetic Sub-cycle Solitons
Three dimensional (3D) relativistic electromagnetic sub-cycle solitons were
observed in 3D Particle-in-Cell simulations of an intense short laser pulse
propagation in an underdense plasma. Their structure resembles that of an
oscillating electric dipole with a poloidal electric field and a toroidal
magnetic field that oscillate in-phase with the electron density with frequency
below the Langmuir frequency. On the ion time scale the soliton undergoes a
Coulomb explosion of its core, resulting in ion acceleration, and then evolves
into a slowly expanding quasi-neutral cavity.Comment: 5 pages, 6 figures;
http://www.ile.osaka-u.ac.jp/research/TSI/Timur/soliton/index.htm
Renormalizing the Schwinger-Dyson equations in the auxiliary field formulation of field theory
In this paper we study the renormalization of the Schwinger-Dyson equations
that arise in the auxiliary field formulation of the O(N) field
theory. The auxiliary field formulation allows a simple interpretation of the
large-N expansion as a loop expansion of the generating functional in the
auxiliary field , once the effective action is obtained by integrating
over the fields. Our all orders result is then used to obtain finite
renormalized Schwinger-Dyson equations based on truncation expansions which
utilize the two-particle irreducible (2-PI) generating function formalism. We
first do an all orders renormalization of the two- and three-point function
equations in the vacuum sector. This result is then used to obtain explicitly
finite and renormalization constant independent self-consistent S-D equations
valid to order~1/N, in both 2+1 and 3+1 dimensions. We compare the results for
the real and imaginary parts of the renormalized Green's functions with the
related \emph{sunset} approximation to the 2-PI equations discussed by Van Hees
and Knoll, and comment on the importance of the Landau pole effect.Comment: 20 pages, 10 figure
Auxiliary field approach to dilute Bose gases with tunable interactions
We rewrite the Lagrangian for a dilute Bose gas in terms of auxiliary fields
related to the normal and anomalous condensate densities. We derive the loop
expansion of the effective action in the composite-field propagators. The
lowest-order auxiliary field (LOAF) theory is a conserving mean-field
approximation consistent with the Goldstone theorem without some of the
difficulties plaguing approximations such as the Hartree and Popov
approximations. LOAF predicts a second-order phase transition. We give a set of
Feynman rules for improving results to any order in the loop expansion in terms
of composite-field propagators. We compare results of the LOAF approximation
with those derived using the Popov approximation. LOAF allows us to explore the
critical regime for all values of the coupling constant and we determine
various parameters in the unitarity limit.Comment: 16 pages, 7 figure
Passive mode locking of a Tm,Ho:KY(WO4)(2) laser around 2 μm
We report the first demonstration, to our knowledge, of passive mode locking in a Tm3+, Ho3+-codoped KYWO42 laser operating in the 2000-2060 nm spectral region. An InGaAsSb-based quantum well semiconductor saturable absorber mirror is used for the initiation and stabilization of the ultrashort pulse generation. Pulses as short as 3.3 ps were generated at 2057 nm with average output powers up to 315 mW at a pulse repetition frequency of 132 MHz for 1.15 W of absorbed pump power at 802 nm from a Ti:sapphire laser
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