4,665 research outputs found
More Effective Field Theory for Nonrelativistic Scattering
An effective field theory treatment of nucleon-nucleon scattering at low
energy shows much promise and could prove a useful tool in the study of nuclear
matter at both ordinary and extreme densities. The analysis is complicated by
the existence a large length scale --- the scattering length --- which arises
due to couplings in the short distance theory being near critical values. I
show how this can be dealt with by introducing an explicit s-channel state in
the effective field theory. The procedure is worked out analytically in a toy
example. I then demonstrate that a simple effective field theory excellently
reproduces the 1S_0 np phase shift up to the pion production threshold.Comment: 15 pages, TeX ; macros: harvmac, eps
Effective Field Theory for Nuclear Physics
I summarize the motivation for the effective field theory approach to nuclear
physics, and highlight some of its recent accomplishments. The results are
compared with those computed in potential models.Comment: Talk delivered at Baryons '98, Bonn, Sept. 22, 1998. 15 pages, 9
figure
Gravitational waves from an early matter era
We investigate the generation of gravitational waves due to the gravitational
instability of primordial density perturbations in an early matter-dominated
era which could be detectable by experiments such as LIGO and LISA. We use
relativistic perturbation theory to give analytic estimates of the tensor
perturbations generated at second order by linear density perturbations. We
find that large enhancement factors with respect to the naive second-order
estimate are possible due to the growth of density perturbations on sub-Hubble
scales. However very large enhancement factors coincide with a breakdown of
linear theory for density perturbations on small scales. To produce a
primordial gravitational wave background that would be detectable with LIGO or
LISA from density perturbations in the linear regime requires primordial
comoving curvature perturbations on small scales of order 0.02 for Advanced
LIGO or 0.005 for LISA, otherwise numerical calculations of the non-linear
evolution on sub-Hubble scales are required.Comment: 23 pages, 2 figure
Nucleon-Nucleon Scattering from Effective Field Theory
We perform a nonperturbative calculation of the 1S0 NN scattering amplitude
using an effective field theory (EFT) expansion. The expansion we advocate is a
modification of what has been used previously; it is no a chiral expansion in
powers of the pion mass. We use dimensional regularization throughout and the
MS-bar subtraction scheme; our final result depends only on physical
observables. We show that the EFT expansion of the quantity |p|cot delta(p)
converges at momenta much greater than the scale that characterizes the
derivative expansion of the EFT Lagrangian. Our conclusions are optimistic
about the applicability of an EFT approach to the quantitative study of nuclear
matter.Comment: Revised discussion of power counting in the EFT expansion. Tex file
uses harvmac, epsf macros, 35 pages with 9 postscript figure
Constraining the Metallicity of the Low Density Lyman-alpha Forest Using OVI Absorption
We search for OVI absorption in a Keck HIRES spectrum of the z=3.62 quasar
Q1422+231. Comparison of CIV measurements to cosmological simulations shows
that \lya forest absorbers with N_HI > 10^{14.5} have [C/H]~=-2.5, for the UV
background spectrum of Haardt & Madau (HM). Lower column density absorption
arises in lower density gas, where OVI is the most sensitive metal tracer.
Since OVI lines lie at wavelengths contaminated by Lyman series absorption, we
interpret our Q1422 results by comparing to artificial spectra drawn from an
SPH simulation of a Lambda-dominated CDM model. A search for deep, narrow
features in Q1422 yields only a few candidate OVI lines, statistically
consistent with the number in artificial spectra with no metals; spectra
generated with the HM background and [O/H] >= -2.5 predict too many narrow
lines. However, applying the optical depth ratio technique of Songaila (1998),
we DO find significant OVI associated with CIV systems; matching Q1422 requires
[O/C]~=+0.5, implying [O/H]~=-2.0. Taken together these results imply that (a)
the metallicity in the low density IGM is at least a factor of three below that
in the overdense regions where CIV absorption is detectable, and (b) oxygen is
overabundant in these regions, consistent with the enrichment pattern of old
halo stars. If the UV background is heavily truncated above 4 Ry, an
implausibly high oxygen overabundance ([O/C]>+2) is required by the data; thus
a majority of the volume of the universe must have undergone helium
reionization by z=3.(Abridged)Comment: Submitted to ApJ, 48 pp including 14 ps figures, uses aaspp4.st
Fourier Analysis of Redshift Space Distortions and the Determination of Omega
The peculiar velocities of galaxies distort the pattern of galaxy clustering
in redshift space, making the redshift space power spectrum anisotropic. In the
linear regime, the strength of this distortion depends only on the ratio , where is the cosmological
density parameter and is the bias parameter. We derive a linear theory
estimator for based on the harmonic moments of the redshift space power
spectrum. Using N-body simulations, we examine the impact of non-linear
gravitational clustering on the power spectrum anisotropy and on our
-estimator. Non-linear effects can be important out to wavelengths
Mpc/h or larger; in most cases, they lower the quadrupole
moment of the power spectrum and thereby depress the estimate of below
the true value. With a sufficiently large redshift survey, the scaling of
non-linear effects may allow separate determinations of and .
We describe a practical technique for measuring the anisotropy of the power
spectrum from galaxy redshift surveys, and we test the technique on mock
catalogues drawn from the N-body simulations. Preliminary application of our
methods to the 1.2 Jy IRAS galaxy survey yields at
wavelengths Mpc/h . Non-linear effects remain important at
these scales, so this estimate of is probably lower than the true
value.Comment: uuencoded compressed postscript fil
Conformal relativity versus Brans-Dicke and superstring theories
Conformal relativity theory which is also known as Hoyle-Narlikar theory has
recently been given some new interest. It is an extended relativity theory
which is invariant with respect to conformal transformations of the metric.
In this paper we show how conformal relativity is related to the Brans-Dicke
theory and to the low-energy-effective superstring theory. We show that
conformal relativity action is equaivalent to a transformed Brans-Dicke action
for Brans-Dicke parameter in contrast to a reduced
(graviton-dilaton) low-energy-effective superstring action which corresponds to
a Brans-Dicke action with Brans-Dicke parameter . In fact,
Brans-Dicke parameter gives a border between a standard scalar
field evolution and a ghost.
We also present basic cosmological solutions of conformal relativity in both
Einstein and string frames. The Eintein limit for flat conformal cosmology
solutions is unique and it is flat Minkowski space. This requires the scalar
field/mass evolution instead of the scale factor evolution in order to explain
cosmological redshift.
It is interesting that like in ekpyrotic/cyclic models, a possible transition
through a singularity in conformal cosmology in the string frame takes place in
the weak coupling regime.Comment: REVTEX4, 12 pages, an improved version, references adde
- …