7,891 research outputs found
Pairing in Nuclei
Simple generic aspects of nuclear pairing in homogeneous medium as well as in
finite nuclei are discussed. It is argued that low-energy nuclear structure is
not sensitive enough to resolve fine details of nuclear nucleon-nucleon (NN)
interaction in general and pairing NN interaction in particular what allows for
regularization of the ultraviolet (high-momentum) divergences and a consistent
formulation of effective superfluid local theory. Some aspects of
(dis)entanglement of pairing with various other effects as well as forefront
ideas concerning isoscalar pairing are also briefly discussed.Comment: Invited talk presented at the International Conference on Finite
Fermionic Systems, Nilsson Model 50 Years,Lund, Sweden, June 14-18, 2005, 7
LaTeX pages, 4 encapsulated postscript figure
Three-dimensional topologically gauged N=6 ABJM type theories
In this paper we construct the conformal supergravity in three
dimensions from a set of Chern-Simons-like terms one for each of the graviton,
gravitino, and R-symmetry gauge field and then couple this theory to the
superconformal ABJM theory. In a first step part of the coupled
Lagrangian for this topologically gauged ABJM theory is derived by demanding
that all terms of third and second order in covariant derivatives cancel in the
supersymmtry variation of the Lagrangian. To achieve this the transformation
rules of the two separate sectors must be augmented by new terms. In a second
step we analyze all terms in that are of first order in covariant
derivatives. The cancelation of these terms require additional terms in the
transformation rules as well as a number of new terms in the Lagrangian. As a
final step we check that all remaining terms in which are bilinear
in fermions cancel which means that the presented Lagrangian and transformation
rules constitute the complete answer. In particular we find in the last step
new terms in the scalar potential containing either one or no structure
constant. The non-derivative higher fermion terms in that have not
yet been completely analyzed are briefly discussed.Comment: 26 pages, v.2 minor corrections, comment on relation to chiral
gravity added
Light-cone analysis of ungauged and topologically gauged BLG theories
We consider three-dimensional maximally superconformal
Bagger-Lambert-Gustavsson (BLG) theory and its topologically gauged version
(constructed recently in arXiv:0809.4478 [hep-th]) in the light-cone gauge.
After eliminating the entire Chern-Simons gauge field, the ungauged BLG theory
looks more conventional and, apart from the order of the interaction terms,
resembles N=4 super-Yang-Mills theory in four dimensions. The light-cone
superspace version of the BLG theory is given to quadratic and quartic order
and some problems with constructing the sixth order interaction terms are
discussed. In the topologically gauged case, we analyze the field equations
related to the three Chern-Simons type terms of N=8 conformal supergravity and
discuss some of the special features of this theory and its couplings to BLG.Comment: 22 pages; v2 some typos correcte
Generalised 11-dimensional supergravity
The low-energy effective dynamics of M-theory, eleven-dimensional supergravity, is taken off-shell in a manifestly supersymmetric superspace formulation. We show that a previously proposed relaxation of the torsion constraints can indeed accomodate a current supermultiplet. We comment on the relation and application of this completely general formalism to higher-derivative (R^4) corrections. This talk was presented by Bengt EW Nilsson at the Triangle Meeting 2000 ``Non-perturbative Methods in Field and String Theory'', NORDITA, Copenhagen, June 19-22, 2000, and by Martin Cederwall at the International Conference ``Quantization, Gauge Theory and Strings'' in memory of Efim Fradkin, Moscow, June 5-10, 2000
An almost isotropic cosmic microwave temperature does not imply an almost isotropic universe
In this letter we will show that, contrary to what is widely believed, an
almost isotropic cosmic microwave background (CMB) temperature does not imply
that the universe is ``close to a Friedmann-Lemaitre universe''. There are two
important manifestations of anisotropy in the geometry of the universe, (i) the
anisotropy in the overall expansion, and (ii) the intrinsic anisotropy of the
gravitational field, described by the Weyl curvature tensor, although the
former usually receives more attention than the latter in the astrophysical
literature. Here we consider a class of spatially homogeneous models for which
the anisotropy of the CMB temperature is within the current observational
limits but whose Weyl curvature is not negligible, i.e. these models are not
close to isotropy even though the CMB temperature is almost isotropic.Comment: 5 pages (AASTeX, aaspp4.sty), submitted to Astrophysical Journal
Letter
The nature of z ~ 2.3 Lyman-alpha emitters
We study the multi-wavelength properties of a set of 171 Ly-alpha emitting
candidates at redshift z = 2.25 found in the COSMOS field, with the aim of
understanding the underlying stellar populations in the galaxies. We especially
seek to understand what the dust contents, ages and stellar masses of the
galaxies are, and how they relate to similar properties of Ly-alpha emitters at
other redshifts. The candidates here are shown to have different properties
from those of Ly-alpha emitters found at higher redshift, by fitting the
spectral energy distributions (SEDs) using a Monte-Carlo Markov-Chain technique
and including nebular emission in the spectra. The stellar masses, and possibly
the dust contents, are higher, with stellar masses in the range log M_* = 8.5 -
11.0 M_sun and A_V = 0.0 - 2.5 mag. Young population ages are well constrained,
but the ages of older populations are typically unconstrained. In 15% of the
galaxies only a single, young population of stars is observed. We show that the
Ly-alpha fluxes of the best fit galaxies are correlated with their dust
properties, with higher dust extinction in Ly-alpha faint galaxies. Testing for
whether results derived from a light-weighted stack of objects correlate to
those found when fitting individual objects we see that stellar masses are
robust to stacking, but ages and especially dust extinctions are derived
incorrectly from stacks. We conclude that the stellar properties of Ly-alpha
emitters at z = 2.25 are different from those at higher redshift and that they
are diverse. Ly-alpha selection appears to be tracing systematically different
galaxies at different redshifts.Comment: 15 pages, 11 figures, 8 tables, accepted in A&A. Table 6 available in
full from the author
Mass-Deformed BLG Theory in Light-Cone Superspace
Maximally supersymmetric mass deformation of the Bagger-Lambert-Gustavsson
(BLG) theory corresponds to a {non-central} extension of the d=3 N=8 Poincare
superalgebra (allowed in three dimensions). We obtain its light-cone superspace
formulation which has a novel feature of the dynamical supersymmetry generators
being {cubic} in the kinematical ones. The mass deformation picks a
quaternionic direction, which breaks the SO(8) R-symmetry down to SO(4)xSO(4).
The Hamiltonian of the theory is shown to be a quadratic form of the dynamical
supersymmetry transformations, to all orders in the mass parameter, M, and the
structure constants, f^{a b c d}.Comment: 23 page
D=3, N=8 conformal supergravity and the Dragon window
We give a superspace description of D=3, N=8 supergravity. The formulation is
off-shell in the sense that the equations of motion are not implied by the
superspace constraints (but an action principle is not given). The multiplet
structure is unconventional, which we connect to the existence of a "Dragon
window", that is modules occurring in the supercurvature but not in the
supertorsion. According to Dragon's theorem this cannot happen above three
dimensions. We clarify the relevance of this window for going on the conformal
shell, and discuss some aspects of coupling to conformal matter.Comment: plain tex, 24 pp v2: minor change
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