1,825 research outputs found
Mate-guarding by male mandrills (Mandrillus sphinx) is associated with female MHC genotype
Female choice for male major histocompatibility complex (MHC) genotype has been widely tested, but the relationship between male mating strategies and female MHC genotype has received far less attention. Moreover, few studies of MHC-associated mate choice test for the fitness effects underlying such choice. We examined mate-guarding by male mandrills, a species with intense male–male competition and female offspring care. We developed a statistical model based on 10 years of observations to describe how the probability a female is mate-guarded varies across her sexual cycle, among cycles and among females. We accounted for female rank, parity, and maternal relatedness. We then tested whether the occurrence of mate-guarding is influenced by 1) MHC dissimilarity, 2) female MHC diversity, and 3) specific female MHC genotypes. Finally, we tested for associations between MHC variables and the ratio of neutrophils to lymphocytes in blood samples taken during routine captures. The best-fit models included either MHC dissimilarity (males were more likely to mate-guard more dissimilar females, and there was some evidence of preference for intermediate MHC dissimilarity) or a specific MHC supertype. Four of 11 supertypes investigated were influential and one had a strong negative influence on mate-guarding. We found some evidence that the MHC genotype that attracted the least mate-guarding was disadvantageous in terms of immune function. However, we did not find evidence that MHC diversity was related to immune function. These results suggest that highly competitive males modify their mating behavior based on female MHC genotype, and a possible fitness benefit to mate choice for specific genotypes
Yang-Mills Solutions on Euclidean Schwarzschild Space
We show that the apparently periodic Charap-Duff Yang-Mills `instantons' in
time-compactified Euclidean Schwarzschild space are actually time independent.
For these solutions, the Yang-Mills potential is constant along the time
direction (no barrier) and therefore, there is no tunneling. We also
demonstrate that the solutions found to date are three dimensional monopoles
and dyons. We conjecture that there are no time-dependent solutions in the
Euclidean Schwarzschild background.Comment: 12 pages, references added, version to appear in PR
Gravitational Waves in a Spatially Closed deSitter Spacetime
Perturbation of gravitational fields may be decomposed into scalar,vector and
tensor components.In this paper we concern with the evolution of tensor mode
perturbations in a spatially closed deSitter background of RW form. It may be
thought as gravitional waves in a classical description. The chosen background
has the advantage of to be maximally extended and symmetric. The spatially flat
models commonly emerge from inflationary scenarios are not completely
extended.We first derive the general weak field equations.Then the form of the
field equations in two special cases, planar and spherical waves are obtained
and their solutions are presented. We conclued with discussing the significance
of the results and their implications.Comment: 16 pages,no figure
Negative Energy in String Theory and Cosmic Censorship Violation
We find asymptotically anti de Sitter solutions in N=8 supergravity which
have negative total energy. This is possible since the boundary conditions
required for the positive energy theorem are stronger than those required for
finite mass (and allowed by string theory). But stability of the anti de Sitter
vacuum is still ensured by the positivity of a modified energy, which includes
an extra surface term. Some of the negative energy solutions describe classical
evolution of nonsingular initial data to naked singularities. Since there is an
open set of such solutions, cosmic censorship is violated generically in
supergravity. Using the dual field theory description, we argue that these
naked singularities will be resolved in the full string theory.Comment: 23 pages, 2 figures, v2: argument for forming naked singularities
clarified, references adde
On a Neutrino Electroweak Radius
We study a combination of amplitudes for neutrino scattering that can isolate
a (gauge-invariant) difference of chirality-preserving neutrino electroweak
radii for and . This involves both photon and
exchange contributions. It is shown that the construction singles out the
contributions of the hypercharge gauge field in the standard model.
We comment on how gauge-dependent terms from the charge radii cancel with other
terms in the relative electroweak radii defined.Comment: 16 pages, revtex with embedded figure
Pinch Technique and the Batalin-Vilkovisky formalism
In this paper we take the first step towards a non-diagrammatic formulation
of the Pinch Technique. In particular we proceed into a systematic
identification of the parts of the one-loop and two-loop Feynman diagrams that
are exchanged during the pinching process in terms of unphysical ghost Green's
functions; the latter appear in the standard Slavnov-Taylor identity satisfied
by the tree-level and one-loop three-gluon vertex. This identification allows
for the consistent generalization of the intrinsic pinch technique to two
loops, through the collective treatment of entire sets of diagrams, instead of
the laborious algebraic manipulation of individual graphs, and sets up the
stage for the generalization of the method to all orders. We show that the task
of comparing the effective Green's functions obtained by the Pinch Technique
with those computed in the background field method Feynman gauge is
significantly facilitated when employing the powerful quantization framework of
Batalin and Vilkovisky. This formalism allows for the derivation of a set of
useful non-linear identities, which express the Background Field Method Green's
functions in terms of the conventional (quantum) ones and auxiliary Green's
functions involving the background source and the gluonic anti-field; these
latter Green's functions are subsequently related by means of a Schwinger-Dyson
type of equation to the ghost Green's functions appearing in the aforementioned
Slavnov-Taylor identity.Comment: 45 pages, uses axodraw; typos corrected, one figure changed, final
version to appear in Phys.Rev.
Energy in Generic Higher Curvature Gravity Theories
We define and compute the energy of higher curvature gravity theories in
arbitrary dimensions. Generically, these theories admit constant curvature
vacua (even in the absence of an explicit cosmological constant), and
asymptotically constant curvature solutions with non-trivial energy properties.
For concreteness, we study quadratic curvature models in detail. Among them,
the one whose action is the square of the traceless Ricci tensor always has
zero energy, unlike conformal (Weyl) gravity. We also study the string-inspired
Einstein-Gauss-Bonnet model and show that both its flat and Anti-de-Sitter
vacua are stable.Comment: 18 pages, typos corrected, one footnote added, to appear in Phys.
Rev.
Localisation of Fermions to brane: Codimension
We investigate dimensional fermionic models in which the system in
codimension- supports a topologically stable solution, and in which the
fermion may be localised to the brane, with power law in 'instanton'
backgrounds and exponentially in 'soliton' backgrounds. When the fermions are
isoscalars, the mechanism fails, while for isospinor fermions it is successful.
As backgrounds we consider instantons of Yang--Mills and sigma models in even
codimensions, solitons of sigma models in odd codimensions, as well as solitons
of Higgs and Goldstone models in all codimensions.Comment: 20 pages latex; expande
The Two-Loop Pinch Technique in the Electroweak Sector
The generalization of the two-loop Pinch Technique to the Electroweak Sector
of the Standard Model is presented. We restrict ourselves to the case of
conserved external currents, and provide a detailed analysis of both the
charged and neutral sectors. The crucial ingredient for this construction is
the identification of the parts discarded during the pinching procedure with
well-defined contributions to the Slavnov-Taylor identity satisfied by the
off-shell one-loop gauge-boson vertices; the latter are nested inside the
conventional two-loop self-energies. It is shown by resorting to a set of
powerful identities that the two-loop effective Pinch Technique self-energies
coincide with the corresponding ones computed in the Background Feynman gauge.
The aforementioned identities are derived in the context of the
Batalin-Vilkovisky formalism, a fact which enables the individual treatment of
the self-energies of the photon and the -boson. Some possible
phenomenological applications are briefly discussed.Comment: 50 pages, uses axodra
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