132 research outputs found
Scalar brane backgrounds in higher order curvature gravity
We investigate maximally symmetric brane world solutions with a scalar field.
Five-dimensional bulk gravity is described by a general lagrangian which yields
field equations containing no higher than second order derivatives. This
includes the Gauss-Bonnet combination for the graviton. Stability and
gravitational properties of such solutions are considered, and we particularily
emphasise the modifications induced by the higher order terms. In particular it
is shown that higher curvature corrections to Einstein theory can give rise to
instabilities in brane world solutions. A method for analytically obtaining the
general solution for such actions is outlined. Genericaly, the requirement of a
finite volume element together with the absence of a naked singularity in the
bulk imposes fine-tuning of the brane tension. A model with a moduli scalar
field is analysed in detail and we address questions of instability and
non-singular self-tuning solutions. In particular, we discuss a case with a
normalisable zero mode but infinite volume element.Comment: published versio
Temperature Dependence of Electric and Magnetic Gluon Condensates
The contribution of Lorentz non-scalar operators to finite temperature
correlation functions is discussed. Using the local duality approach for the
one-pion matrix element of a product of two vector currents, the temperature
dependence of the average gluonic stress tensor is estimated in the chiral
limit to be . At a
normalization point GeV we obtain . Together with the
known temperature dependence of the Lorentz scalar gluon condensate we are able
to infer and separately
in the low-temperature hadronic phase.Comment: 11 pages, TPI-MINN-92/37-
Scalar susceptibility and chiral symmetry restoration in nuclei
We study the nuclear modification of the scalar QCD susceptibility,
calculated as the derivative of the quark condensate with respect to the quark
mass. We show that it has two origins. One is the low lying nuclear
excitations. At normal nuclear density this part is constrained by the nuclear
incompressibility. The other part arises from the individual nucleon response
and it is dominated by the pion cloud contribution. Numerically the first
contribution dominates. The resulting increase in magnitude of the scalar
susceptibility at normal density is such that it becomes close to the
pseudoscalar susceptibility, while it is quite different in the vacuum. We
interpret it as a consequence of chiral symmetry restoration in nuclei.Comment: 17 pages, 5 figure
Dilepton Spectra from Decays of Light Unflavored Mesons
The invariant mass spectrum of the and pairs
from decays of light unflavored mesons with masses below the -meson mass to final states containing along with a dilepton pair one
photon, one meson, and two mesons are calculated within the framework of the
effective meson theory. The results can be used for simulations of the dilepton
spectra in heavy-ion collisions and for experimental searches of dilepton meson
decays.Comment: 73 pages, 19 figures, 3 tables, REVTeX, new references adde
Electroweak Radiative Corrections to Parity-Violating Electroexcitation of the
We analyze the degree to which parity-violating (PV) electroexcitation of the
resonance may be used to extract the weak neutral axial vector
transition form factors. We find that the axial vector electroweak radiative
corrections are large and theoretically uncertain, thereby modifying the
nominal interpretation of the PV asymmetry in terms of the weak neutral form
factors. We also show that, in contrast to the situation for elastic electron
scattering, the axial PV asymmetry does not vanish at the photon
point as a consequence of a new term entering the radiative corrections. We
argue that an experimental determination of these radiative corrections would
be of interest for hadron structure theory, possibly shedding light on the
violation of Hara's theorem in weak, radiative hyperon decays.Comment: RevTex, 76 page
QCD sum rule for nucleon in nuclear matter
We consider the two-point function of nucleon current in nuclear matter and
write a QCD sum rule to analyse the residue of the nucleon pole as a function
of nuclear density. The nucleon self-energy needed for the sum rule is taken as
input from calculations using phenomenological NN potential. Our result shows a
decrease in the residue with increasing nuclear density, as is known to be the
case with similar quantities
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
Kaon Production and Kaon to Pion Ratio in Au+Au Collisions at \snn=130 GeV
Mid-rapidity transverse mass spectra and multiplicity densities of charged
and neutral kaons are reported for Au+Au collisions at \snn=130 GeV at RHIC.
The spectra are exponential in transverse mass, with an inverse slope of about
280 MeV in central collisions. The multiplicity densities for these particles
scale with the negative hadron pseudo-rapidity density. The charged kaon to
pion ratios are and
for the most central collisions. The ratio is lower than the same
ratio observed at the SPS while the is higher than the SPS result.
Both ratios are enhanced by about 50% relative to p+p and +p
collision data at similar energies.Comment: 6 pages, 3 figures, 1 tabl
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
Azimuthal anisotropy: the higher harmonics
We report the first observations of the fourth harmonic (v_4) in the
azimuthal distribution of particles at RHIC. The measurement was done taking
advantage of the large elliptic flow generated at RHIC. The integrated v_4 is
about a factor of 10 smaller than v_2. For the sixth (v_6) and eighth (v_8)
harmonics upper limits on the magnitudes are reported.Comment: 4 pages, 6 figures, contribution to the Quark Matter 2004 proceeding
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