47,159 research outputs found
Face processing limitation to own species in primates: a comparative study in brown capuchins, Tonkean macaques and humans
Most primates live in social groups which survival and stability depend on
individuals' abilities to create strong social relationships with other group
members. The existence of those groups requires to identify individuals and to
assign to each of them a social status. Individual recognition can be achieved
through vocalizations but also through faces. In humans, an efficient system
for the processing of own species faces exists. This specialization is achieved
through experience with faces of conspecifics during development and leads to
the loss of ability to process faces from other primate species. We hypothesize
that a similar mechanism exists in social primates. We investigated face
processing in one Old World species (genus Macaca) and in one New World species
(genus Cebus). Our results show the same advantage for own species face
recognition for all tested subjects. This work suggests in all species tested
the existence of a common trait inherited from the primate ancestor: an
efficient system to identify individual faces of own species only
Empirical Processes of Multidimensional Systems with Multiple Mixing Properties
We establish a multivariate empirical process central limit theorem for
stationary -valued stochastic processes under very weak
conditions concerning the dependence structure of the process. As an
application we can prove the empirical process CLT for ergodic torus
automorphisms. Our results also apply to Markov chains and dynamical systems
having a spectral gap on some Banach space of functions. Our proof uses a
multivariate extension of the techniques introduced by Dehling, Durieu and
Voln\'y \cite{DehDurVol09} in the univariate case. As an important technical
ingredient, we prove a th moment bound for partial sums in multiple
mixing systems.Comment: to be published in Stochastic Processes and their Application
Harmonic spinors and local deformations of the metric
Let (M,g) be a compact Riemannian spin manifold. The Atiyah-Singer index
theorem yields a lower bound for the dimension of the kernel of the Dirac
operator. We prove that this bound can be attained by changing the Riemannian
metric g on an arbitrarily small open set.Comment: minor changes, to appear in Mathematical Research Letter
On higher dimensional black holes with abelian isometry group
We consider (n+1)--dimensional, stationary, asymptotically flat, or
Kaluza-Klein asymptotically flat black holes, with an abelian --dimensional
subgroup of the isometry group satisfying an orthogonal integrability
condition. Under suitable regularity conditions we prove that the area of the
group orbits is positive on the domain of outer communications, vanishing only
on its boundary and on the "symmetry axis". We further show that the orbits of
the connected component of the isometry group are timelike throughout the
domain of outer communications. Those results provide a starting point for the
classification of such black holes. Finally, we show non-existence of zeros of
static Killing vectors on degenerate Killing horizons, as needed for the
generalisation of the static no-hair theorem to higher dimensions
Spontaneous electromagnetic superconductivity and superfluidity of QCDxQED vacuum in strong magnetic field
It was recently shown that the vacuum in the background of a strong enough
magnetic field may become an electromagnetic superconductor due to interplay
between strong and electromagnetic forces. The superconducting ground state of
the QCDxQED sector of the vacuum is associated with magnetic-field-assisted
emergence of quark-antiquark condensates which carry quantum numbers of charged
rho mesons (i.e., of electrically charged vector particles made of lightest, u
and d, quarks and antiquarks). Here we demonstrate that this exotic
electromagnetic superconductivity of vacuum is also accompanied by even more
exotic superfluidity of the neutral rho mesons. The superfluid component --
despite being electrically neutral -- turns out to be sensitive to an external
electric field as the superfluid may ballistically be accelerated by a test
background electric field along the magnetic-field axis. In the ground state
both superconducting and superfluid components are inhomogeneous periodic
functions of the transversal (with respect to the axis of the magnetic field)
spatial coordinates. The superconducting part of the ground state resembles an
Abrikosov ground state in a type-II superconductor: the superconducting
condensate organizes itself in periodic structure which possesses the symmetry
of an equilateral triangular lattice. Each elementary lattice cell contains a
stringlike topological defect (superconductor vortex) in the charged rho
condensates as well as three superfluid vortices and three superfluid
antivortices made of the neutral rho condensate. The superposition of the
superconductor and superfluid vortex lattices has a complicated "kaleidoscopic"
pattern.Comment: 6 pages, 2 figures. Talk given at Sixth International Conference on
Quarks and Nuclear Physics QNP2012, April 16-20, 2012, Ecole Polytechnique,
Palaiseau, Franc
Collisions of Shock Waves in General Relativity
We show that the Nariai-Bertotti Petrov type D, homogeneous solution of
Einstein's vacuum field equations with a cosmological constant describes the
space-time in the interaction region following the head-on collision of two
homogeneous, plane gravitational shock waves each initially traveling in a
vacuum containing no cosmological constant. A shock wave in this context has a
step function profile in contrast to an impulsive wave which has a delta
function profile. Following the collision two light-like signals, each composed
of a plane, homogeneous light-like shell of matter and a plane, homogeneous
impulsive gravitational wave, travel away from each other and a cosmological
constant is generated in the interaction region. Furthermore a plane,
light-like signal consisting of an electromagnetic shock wave accompanying a
gravitational shock wave is described with the help of two real parameters, one
for each wave. The head-on collision of two such light-like signals is examined
and we show that if a simple algebraic relation is satisfied between the two
pairs of parameters associated with each incoming light-like signal then the
space-time in the interaction region following the collision is a Bertotti
space-time which is a homogeneous solution of the vacuum Einstein-Maxwell field
equations with a cosmological constant.Comment: Latex file, 10 page
Eigenvalues estimate for the Neumann problem on bounded domains
In this note, we investigate upper bounds of the Neumann eigenvalue problem
for the Laplacian of a bounded domain (with smooth boundary) in a given
complete (not compact a priori) Riemannian manifold with Ricci bounded below .
For this, we use test functions for the Rayleigh quotient subordinated to a
family of open sets constructed in a general metric way, interesting for
itself. As application, we get upper bounds for the Neumann spectrum which is
clearly in agreement with the Weyl law and which is analogous to Buser's upper
bounds of the spectrum of a closed Riemannian manifold with lower bound on the
Ricci curvature.Comment: 9 pages, submitted december 200
Domain deformations and eigenvalues of the Dirichlet Laplacian in a Riemannian manifold
For any bounded regular domain of a real analytic Riemannian
manifold , we denote by the -th eigenvalue of the
Dirichlet Laplacian of . In this paper, we consider and as
a functional upon the set of domains of fixed volume in . We introduce and
investigate a natural notion of critical domain for this functional. In
particular, we obtain necessary and sufficient conditions for a domain to be
critical, locally minimizing or locally maximizing for . These
results rely on Hadamard type variational formulae that we establish in this
general setting.Comment: To appear in Illinois J. Mat
Einstein-Maxwell-Dilaton theories with a Liouville potential
We find and analyse solutions of Einstein's equations in arbitrary d
dimensions and in the presence of a scalar field with a Liouville potential
coupled to a Maxwell field. We consider spacetimes of cylindrical symmetry or
again subspaces of dimension d-2 with constant curvature and analyse in detail
the field equations and manifest their symmetries. The field equations of the
full system are shown to reduce to a single or couple of ODE's which can be
used to solve analytically or numerically the theory for the symmetry at hand.
Further solutions can also be generated by a solution generating technique akin
to the EM duality in the absence of a cosmological constant. We then find and
analyse explicit solutions including black holes and gravitating solitons for
the case of four dimensional relativity and the higher-dimensional oxydised
5-dimensional spacetime. The general solution is obtained for a certain
relation between couplings in the case of cylindrical symmetry.Comment: v3, Some typos corrected with respect to the published versio
Quantum metric fluctuations and Hawking radiation
In this Letter we study the gravitational interactions between outgoing
configurations giving rise to Hawking radiation and in-falling configurations.
When the latter are in their ground state, the near horizon interactions lead
to collective effects which express themselves as metric fluctuations and which
induce dissipation, as in Brownian motion. This dissipation prevents the
appearance of trans-Planckian frequencies and leads to a description of Hawking
radiation which is very similar to that obtained from sound propagation in
condensed matter models.Comment: 4 pages, revte
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