558 research outputs found
Center of mass integral in canonical general relativity
For a two-surface B tending to an infinite--radius round sphere at spatial
infinity, we consider the Brown--York boundary integral H_B belonging to the
energy sector of the gravitational Hamiltonian. Assuming that the lapse
function behaves as N \sim 1 in the limit, we find agreement between H_B and
the total Arnowitt--Deser--Misner energy, an agreement first noted by Braden,
Brown, Whiting, and York. However, we argue that the Arnowitt--Deser--Misner
mass--aspect differs from a gauge invariant mass--aspect by a pure divergence
on the unit sphere. We also examine the boundary integral H_B corresponding to
the Hamiltonian generator of an asymptotic boost, in which case the lapse N
\sim x^k grows like one of the asymptotically Cartesian coordinate functions.
Such an integral defines the kth component of the center of mass for a Cauchy
surface \Sigma bounded by B. In the large--radius limit, we find agreement
between H_B and an integral introduced by Beig and O'Murchadha. Although both
H_B and the Beig--O'Murchadha integral are naively divergent, they are in fact
finite modulo the Hamiltonian constraint. Furthermore, we examine the
relationship between H_B and a certain two--surface integral linear in the
spacetime Riemann curvature tensor. Similar integrals featuring the curvature
appear in works by Ashtekar and Hansen, Penrose, Goldberg, and Hayward. Within
the canonical 3+1 formalism, we define gravitational energy and
center--of--mass as certain moments of Riemann curvature.Comment: 52 pages, revtex4, uses amsmath and amssym
Diffeomorphism Invariance in the Hamiltonian formulation of General Relativity
It is shown that when the Einstein-Hilbert Lagrangian is considered without
any non-covariant modifications or change of variables, its Hamiltonian
formulation leads to results consistent with principles of General Relativity.
The first-class constraints of such a Hamiltonian formulation, with the metric
tensor taken as a canonical variable, allow one to derive the generator of
gauge transformations, which directly leads to diffeomorphism invariance. The
given Hamiltonian formulation preserves general covariance of the
transformations derivable from it. This characteristic should be used as the
crucial consistency requirement that must be met by any Hamiltonian formulation
of General Relativity.Comment: 13 page
Superfluid transition in quasi2D Fermi gases
We show that atomic Fermi gases in quasi2D geometries are promising for
achieving superfluidity. In the regime of BCS pairing for weak attraction, we
calculate the critical temperature T_c and analyze possibilities of increasing
the ratio of T_c to the Fermi energy. In the opposite limit, where a strong
coupling leads to the formation of weakly bound quasi2D dimers, we find that
their Bose-Einstein condensate will be stable on a long time scale.Comment: 4 pages, 1 figur
Probing Sub-Micron Forces by Interferometry of Bose-Einstein Condensed Atoms
We propose a technique, using interferometry of Bose-Einstein condensed
alkali atoms, for the detection of sub-micron-range forces. It may extend
present searches at 1 micron by 6 to 9 orders of magnitude, deep into the
theoretically interesting regime of 1000 times gravity. We give several
examples of both four-dimensional particles (moduli), as well as
higher-dimensional particles -- vectors and scalars in a large bulk-- that
could mediate forces accessible by this technique.Comment: 32 pages, 5 figures, RevTeX4, expanded discussion of interactions,
references added, to appear in PR
Axes determination for segmented true-coaxial HPGe detectors
A fast method to determine the crystallographic axes of segmented
true-coaxial high-purity germanium detectors is presented. It is based on the
analysis of segment-occupancy patterns obtained by irradiation with radioactive
sources. The measured patterns are compared to predictions for different axes
orientations. The predictions require a simulation of the trajectories of the
charge carriers taking the transverse anisotropy of their drift into account.Comment: 18 pages, 1 table, 31 figures; included background contribution to
the occupancy patterns and systematic uncertainties, results slightly change
Crossovers in Unitary Fermi Systems
Universality and crossover is described for attractive and repulsive
interactions where, respectively, the BCS-BEC crossover takes place and a
ferromagnetic phase transition is claimed. Crossovers are also described for
optical lattices and multicomponent systems. The crossovers, universal
parameters and phase transitions are described within the Leggett and NSR
models and calculated in detail within the Jastrow-Slater approximation. The
physics of ultracold Fermi atoms is applied to neutron, nuclear and quark
matter, nuclei and electrons in solids whenever possible. Specifically, the
differences between optical lattices and cuprates is discussed w.r.t.
antiferromagnetic, d-wave superfluid phases and phase separation.Comment: 50 pages, 15 figures. Contribution to Lecture Notes in Physics
"BCS-BEC crossover and the Unitary Fermi Gas" edited by W. Zwerge
Measurement of the Charged Multiplicities in b, c and Light Quark Events from Z0 Decays
Average charged multiplicities have been measured separately in , and
light quark () events from decays measured in the SLD experiment.
Impact parameters of charged tracks were used to select enriched samples of
and light quark events, and reconstructed charmed mesons were used to select
quark events. We measured the charged multiplicities:
,
, from
which we derived the differences between the total average charged
multiplicities of or quark events and light quark events: and . We compared
these measurements with those at lower center-of-mass energies and with
perturbative QCD predictions. These combined results are in agreement with the
QCD expectations and disfavor the hypothesis of flavor-independent
fragmentation.Comment: 19 pages LaTex, 4 EPS figures, to appear in Physics Letters
Measurement of and charged current inclusive cross sections and their ratio with the T2K off-axis near detector
We report a measurement of cross section and the first measurements of the cross section
and their ratio
at (anti-)neutrino energies below 1.5
GeV. We determine the single momentum bin cross section measurements, averaged
over the T2K -flux, for the detector target material (mainly
Carbon, Oxygen, Hydrogen and Copper) with phase space restricted laboratory
frame kinematics of 500 MeV/c. The
results are and $\sigma(\nu)=\left( 2.41\
\pm0.022{\rm{(stat.)}}\pm0.231{\rm (syst.)}\ \right)\times10^{-39}^{2}R\left(\frac{\sigma(\bar{\nu})}{\sigma(\nu)}\right)=
0.373\pm0.012{\rm (stat.)}\pm0.015{\rm (syst.)}$.Comment: 18 pages, 8 figure
Demonstration of the temporal matter-wave Talbot effect for trapped matter waves
We demonstrate the temporal Talbot effect for trapped matter waves using
ultracold atoms in an optical lattice. We investigate the phase evolution of an
array of essentially non-interacting matter waves and observe matter-wave
collapse and revival in the form of a Talbot interference pattern. By using
long expansion times, we image momentum space with sub-recoil resolution,
allowing us to observe fractional Talbot fringes up to 10th order.Comment: 17 pages, 7 figure
Azimuthal anisotropy and correlations in p+p, d+Au and Au+Au collisions at 200 GeV
We present the first measurement of directed flow () at RHIC. is
found to be consistent with zero at pseudorapidities from -1.2 to 1.2,
then rises to the level of a couple of percent over the range . The latter observation is similar to data from NA49 if the SPS rapidities
are shifted by the difference in beam rapidity between RHIC and SPS.
Back-to-back jets emitted out-of-plane are found to be suppressed more if
compared to those emitted in-plane, which is consistent with {\it jet
quenching}. Using the scalar product method, we systematically compared
azimuthal correlations from p+p, d+Au and Au+Au collisions. Flow and non-flow
from these three different collision systems are discussed.Comment: Quark Matter 2004 proceeding, 4 pages, 3 figure
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