418 research outputs found
Relativistic nuclear structure effects in quasielastic neutrino scattering
Charged-current cross sections are calculated for quasielastic neutrino and
antineutrino scattering using a relativistic meson-nucleon model. We examine
how nuclear-structure effects, such as relativistic random-phase-approximation
(RPA) corrections and momentum-dependent nucleon self-energies, influence the
extraction of the axial form factor of the nucleon. RPA corrections are
important only at low-momentum transfers. In contrast, the momentum dependence
of the relativistic self-energies changes appreciably the value of the
axial-mass parameter, , extracted from dipole fits to the axial form
factor. Using Brookhaven's experimental neutrino spectrum we estimate the
sensitivity of M to various relativistic nuclear-structure effects.Comment: 26 pages, revtex, 6 postscript figures (available upon request
Macroscopic superstrings as interpolating solitons
It is known that, in string sigma-model metric, the `extreme' fivebrane
solution of D=10 supergravity interpolates between D=10 Minkowski spacetime and
a supersymmetric compactification to a linear dilaton vacuum. We show
here that, in {\it fivebrane} sigma-model metric, the extreme string solution
of D=10 supergravity interpolates between Minkowski spacetime and a hitherto
unknown supersymmetric compactification of d=10 supergravity to a
three-dimensional anti-de Sitter generalization of the linear dilaton vacuum,
which may be invariantly characterized in terms of conformal
Killing vectors. The dilaton field diverges near the string core but this
divergence may be eliminated by re-interpreting the string solution as the
extreme membrane solution of 11-dimensional supergravity. We show that the
latter has an analytic extension through a regular degenerate event horizon to
an interior region containing a curvature singularity. We obtain analogous
results for other extended object solutions of supergravity theories.Comment: 12 page
String and Fivebrane Solitons: Singular or Non-singular?
We ask whether the recently discovered superstring and superfivebrane
solutions of D=10 supergravity admit the interpretation of non-singular
solitons even though, in the absence of Yang-Mills fields, they exhibit
curvature singularities at the origin. We answer the question using a test
probe/source approach, and find that the nature of the singularity is
probe-dependent. If the test probe and source are both superstrings or both
superfivebranes, one falls into the other in a finite proper time and the
singularity is real, whereas if one is a superstring and the other a
superfivebrane it takes an infinite proper time (the force is repulsive!) and
the singularity is harmless. Black strings and fivebranes, on the other hand,
always display real singularities.Comment: 15 page
Inclusive Nucleon Emission Induced by Quasi--Elastic Neutrino--Nucleus Interactions
We study the quasi--elastic contribution to the inclusive ,
, and
reactions in nuclei using a Monte Carlo simulation method to account for the
rescattering of the outgoing nucleon. As input, we take the reaction
probability from the microscopical many body framework developed in Phys. Rev.
{\bf C70} (2004) 055503 for charged-current induced reactions, while for
neutral currents we use results from a natural extension of the model described
in that reference. The nucleon emission process studied here is a clear signal
for neutral--current neutrino driven reactions, that can be used in the
analysis of future neutrino experiments.Comment: 23 pages, 17 figures; Version 2: few typos correcte
Solitonic Strings and BPS Saturated Dyonic Black Holes
We consider a six-dimensional solitonic string solution described by a
conformal chiral null model with non-trivial superconformal transverse
part. It can be interpreted as a five-dimensional dyonic solitonic string wound
around a compact fifth dimension. The conformal model is regular with the
short-distance (`throat') region equivalent to a WZW theory. At distances
larger than the compactification scale the solitonic string reduces to a dyonic
static spherically-symmetric black hole of toroidally compactified heterotic
string. The new four-dimensional solution is parameterised by five charges,
saturates the Bogomol'nyi bound and has nontrivial dilaton-axion field and
moduli fields of two-torus. When acted by combined T- and S-duality
transformations it serves as a generating solution for all the static
spherically-symmetric BPS-saturated configurations of the low-energy heterotic
string theory compactified on six-torus. Solutions with regular horizons have
the global space-time structure of extreme Reissner-Nordstrom black holes with
the non-zero thermodynamic entropy which depends only on conserved (quantised)
charge vectors. The independence of the thermodynamic entropy on moduli and
axion-dilaton couplings strongly suggests that it should have a microscopic
interpretation as counting degeneracy of underlying string configurations. This
interpretation is supported by arguments based on the corresponding
six-dimensional conformal field theory. The expression for the level of the WZW
theory describing the throat region implies a renormalisation of the string
tension by a product of magnetic charges, thus relating the entropy and the
number of oscillations of the solitonic string in compact directions.Comment: 27 Pages, uses RevTeX (solution for the axion field corrected,
erratum to appear in Phys. Rev. D
The Black Branes of M-theory
We present a class of black -brane solutions of M-theory which were
hitherto known only in the extremal supersymmetric limit, and calculate their
macroscopic entropy and temperature.Comment: Latex, 13 pages, minor corrections and reference adde
Relativistic mean-field study of neutron-rich nuclei
A relativistic mean-field model is used to study the ground-state properties
of neutron-rich nuclei. Nonlinear isoscalar-isovector terms, unconstrained by
present day phenomenology, are added to the model Lagrangian in order to modify
the poorly known density dependence of the symmetry energy. These new terms
soften the symmetry energy and reshape the theoretical neutron drip line
without compromising the agreement with existing ground-state information. A
strong correlation between the neutron radius of 208Pb and the binding energy
of valence orbitals is found: the smaller the neutron radius of 208Pb, the
weaker the binding energy of the last occupied neutron orbital. Thus, models
with the softest symmetry energy are the first ones to drip neutrons. Further,
in anticipation of the upcoming one-percent measurement of the neutron radius
of 208Pb at the Thomas Jefferson Laboratory, a close relationship between the
neutron radius of 208Pb and neutron radii of elements of relevance to atomic
parity-violating experiments is established.Comment: 14 pages, 5 figure
Crossover effects in a discrete deposition model with Kardar-Parisi-Zhang scaling
We simulated a growth model in 1+1 dimensions in which particles are
aggregated according to the rules of ballistic deposition with probability p or
according to the rules of random deposition with surface relaxation (Family
model) with probability 1-p. For any p>0, this system is in the
Kardar-Parisi-Zhang (KPZ) universality class, but it presents a slow crossover
from the Edwards-Wilkinson class (EW) for small p. From the scaling of the
growth velocity, the parameter p is connected to the coefficient of the
nonlinear term of the KPZ equation, lambda, giving lambda ~ p^gamma, with gamma
= 2.1 +- 0.2. Our numerical results confirm the interface width scaling in the
growth regime as W ~ lambda^beta t^beta, and the scaling of the saturation time
as tau ~ lambda^(-1) L^z, with the expected exponents beta =1/3 and z=3/2 and
strong corrections to scaling for small lambda. This picture is consistent with
a crossover time from EW to KPZ growth in the form t_c ~ lambda^(-4) ~ p^(-8),
in agreement with scaling theories and renormalization group analysis. Some
consequences of the slow crossover in this problem are discussed and may help
investigations of more complex models.Comment: 16 pages, 7 figures; to appear in Phys. Rev.
Born-Infeld strings between D-branes
We examine the solutions of world-volume action for a D3-brane being put near
other D3-brane which is replaced by the background configuration of bulk space.
It is shown that the BPS solutions are not affected by the D3-brane background,
and they are interpreted as dyonic strings connecting two branes. On the
contrary, the non-BPS configurations are largely influenced by the background
D-brane, and we find that the solutions with pure electric charge cannot
connect two branes. These solutions are corresponding to the bound state of
brane and anti-brane which has been found by Callan and MaldacenaComment: 14 pages, 8 figure
Intersecting D-Branes in ten and six dimensions
We show how, via -duality, intersecting -Brane configurations in ten
(six) dimensions can be obtained from the elementary -Brane configurations
by embedding a Type IIB -Brane into a Type IIB Nine-Brane (Five-Brane) and
give a classification of such configurations. We show that only a very specific
subclass of these configurations can be realized as (supersymmetric) solutions
to the equations of motion of IIA/IIB supergravity. Whereas the elementary
-brane solutions in are characterized by a single harmonic function,
those in contain two independent harmonic functions and may be viewed as
the intersection of two elementary -branes. Using
string/string/string triality in six dimensions we show that the heterotic
version of the elementary -Brane solutions correspond in ten
dimensions to intersecting Neveu-Schwarz/Neveu-Schwarz (NS/NS) strings or
five-branes and their -duals. We comment on the implications of our results
in other than ten and six dimensions.Comment: 18 pages, Latex, (substantial changes in section 2
- …