241 research outputs found
Moduli Corrections to Gauge and Gravitational Couplings in four dimensional Superstrings
We study one-loop, moduli-dependent corrections to gauge and gravitational
couplings in supersymmetric vacua of the heterotic string. By exploiting their
relation to the integrability condition for the associated CP-odd couplings, we
derive general expressions for them, both for and models, in
terms of tree level four-point functions in the internal superconformal
theory. The case, in particular symmetric orbifolds, is discussed in
detail.Comment: 19 page
Macromolecular theory of solvation and structure in mixtures of colloids and polymers
The structural and thermodynamic properties of mixtures of colloidal spheres
and non-adsorbing polymer chains are studied within a novel general
two-component macromolecular liquid state approach applicable for all size
asymmetry ratios. The dilute limits, when one of the components is at infinite
dilution but the other concentrated, are presented and compared to field theory
and models which replace polymer coils with spheres. Whereas the derived
analytical results compare well, qualitatively and quantitatively, with
mean-field scaling laws where available, important differences from ``effective
sphere'' approaches are found for large polymer sizes or semi-dilute
concentrations.Comment: 23 pages, 10 figure
Moduli Corrections to Gravitational Couplings from String loops
We study moduli dependent threshold corrections to gravitational couplings in
the case of the heterotic string compactified on a symmetric orbifold, for
untwisted moduli, extending previous analysis on gauge couplings. Like in the
gauge case, the contribution comes entirely from the spacetime sector. As
a byproduct, this calculation provides a simple derivation of the trace anomaly
coefficients for the different fields coupled to gravity.Comment: 9 page
Classification of Effective Neutrino Mass Operators
We present a classification of SU(3) x SU(2) x U(1) gauge invariant \Delta L
= 2 (L being lepton number) effective operators relevant for generating small
Majorana neutrino masses. Operators of dimension up to 11 have been included in
our analysis. This approach enables us to systematically identify interesting
neutrino mass models. It is shown that many of the well-known models fall into
this classification. In addition, a number of new models are proposed and their
neutrino phenomenology is outlined. Of particular interest is a large class of
models in which neutrinoless double beta decays arise at a lower order compared
to the neutrino mass, making these decays accessible to the current round of
experiments.Comment: 34 pages in RevTeX with 18 figure
Topological Amplitudes in String Theory
We show that certain type II string amplitudes at genus are given by the
topological partition function discussed recently by Bershadsky, Cecotti,
Ooguri and Vafa. These amplitudes give rise to a term in the four-dimensional
effective action of the form , where is the chiral
superfield of supergravitational multiplet. The holomorphic anomaly of
is related to non-localities of the effective action due to the
propagation of massless states. This result generalizes the holomorphic anomaly
of the one loop case which is known to lead to non-harmonic gravitational
couplings.Comment: 31 pages (LATEX) + 2 figures (available upon request as PS file or
hardcopy), NUB-3071 - IC/93/202 - CPTH-A258.079
Continuous image distortion by astrophysical thick lenses
Image distortion due to weak gravitational lensing is examined using a
non-perturbative method of integrating the geodesic deviation and optical
scalar equations along the null geodesics connecting the observer to a distant
source. The method we develop continuously changes the shape of the pencil of
rays from the source to the observer with no reference to lens planes in
astrophysically relevant scenarios. We compare the projected area and the ratio
of semi-major to semi-minor axes of the observed elliptical image shape for
circular sources from the continuous, thick-lens method with the commonly
assumed thin-lens approximation. We find that for truncated singular isothermal
sphere and NFW models of realistic galaxy clusters, the commonly used thin-lens
approximation is accurate to better than 1 part in 10^4 in predicting the image
area and axes ratios. For asymmetric thick lenses consisting of two massive
clusters separated along the line of sight in redshift up to \Delta z = 0.2, we
find that modeling the image distortion as two clusters in a single lens plane
does not produce relative errors in image area or axes ratio more than 0.5%Comment: accepted to GR
Effective Mu-Term in Superstring Theory
In four-dimensional compactifications of the heterotic superstring theory the
K\"ahler potential has a form which generically induces a superpotential mass
term for Higgs particles once supersymmetry is broken at low energies. This
``-term'' is analyzed in a model-independent way at the tree level and in
the one-loop approximation, and explicit expressions are obtained for orbifold
compactifications. Additional contributions which arise in the case of
supersymmetry breaking induced by gaugino condensation are also discussed.Comment: 28 pages (LaTeX, 2 figures attached as uuencoded ps files), NUB-3084
- IC/94/72 - CPTH-A282.0194, to appear in Nuclear Physics B (revised version
contains modifications due to the presence of extra massless states at some
special points of the moduli space in orbifold models
Algebraic approach to quantum black holes: logarithmic corrections to black hole entropy
The algebraic approach to black hole quantization requires the horizon area
eigenvalues to be equally spaced. As shown previously, for a neutral
non-rotating black hole, such eigenvalues must be -fold degenerate if
one constructs the black hole stationary states by means of a pair of creation
operators subject to a specific algebra. We show that the algebra of these two
building blocks exhibits symmetry, where the area
operator generates the U(1) symmetry. The three generators of the SU(2)
symmetry represent a {\it global} quantum number (hyperspin) of the black hole,
and we show that this hyperspin must be zero. As a result, the degeneracy of
the -th area eigenvalue is reduced to for large , and
therefore, the logarithmic correction term should be added to the
Bekenstein-Hawking entropy. We also provide a heuristic approach explaining
this result, and an evidence for the existence of {\it two} building blocks.Comment: 15 pages, Revtex, to appear in Phys. Rev.
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