179 research outputs found
Constraints on dark energy and cosmic topology
A non-trivial spatial topology of the Universe is a potentially observable
attribute, which can be probed through the circles-in-the-sky for all locally
homogeneous and isotropic universes with no assumptions on the cosmological
parameters. We show how one can use a possible circles-in-the-sky detection of
the spatial topology of globally homogeneous universes to set constraints on
the dark energy equation of state parameters.Comment: 6 pages, 1 figure. To appear in Int. J. Mod. Phys. A (2009). From a
talk presented at the Seventh Alexander Friedmann International Seminar on
Gravitation and Cosmolog
DRA method: Powerful tool for the calculation of the loop integrals
We review the method of the calculation of multiloop integrals suggested in
Ref.\cite{Lee2010}.Comment: 6 pages, contribution to ACAT2011 proceedings, Uxbridge, London,
September 5-9, 2011, typos are correcte
Observational constraints on modified gravity models and the Poincar\'e dodecahedral topology
We study the constraints that spatial topology may place on the parameters of
models that account for the accelerated expansion of the universe via infrared
modifications to general relativity, namely the Dvali-Gabadadze-Porrati
braneworld model as well as the Dvali-Turner and Cardassian models. By
considering the Poincar\'e dodecahedral space as the circles-in-the-sky
observable spatial topology, we examine the constraints that can be placed on
the parameters of each model using type Ia supernovae data together with the
baryon acoustic peak in the large scale correlation function of the Sloan
Digital Sky Survey of luminous red galaxies and the Cosmic Microwave Background
Radiation shift parameter data. We show that knowledge of spatial topology does
provide relevant constraints, particularly on the curvature parameter, for all
models.Comment: Revtex4, 10 pages, 1 table, 12 figures; version to match the one to
be published in Physical Review
Ground states of supersymmetric Yang-Mills-Chern-Simons theory
We consider minimally supersymmetric Yang-Mills theory with a Chern-Simons
term on a flat spatial two-torus. The Witten index may be computed in the weak
coupling limit, where the ground state wave-functions localize on the moduli
space of flat gauge connections. We perform such computations by considering
this moduli space as an orbifold of a certain flat complex torus. Our results
agree with those obtained previously by instead considering the moduli space as
a complex projective space. An advantage of the present method is that it
allows for a more straightforward determination of the discrete electric 't
Hooft fluxes of the ground states in theories with non-simply connected gauge
groups. A consistency check is provided by the invariance of the results under
the mapping class group of a (Euclidean) three-torus.Comment: 18 page
Constraints on the cosmological density parameters and cosmic topology
A nontrivial topology of the spatial section of the universe is an
observable, which can be probed for all locally homogeneous and isotropic
universes, without any assumption on the cosmological density parameters. We
discuss how one can use this observable to set constraints on the density
parameters of the Universe by using a specific spatial topology along with type
Ia supenovae and X-ray gas mass fraction data sets.Comment: 11 pages, 4 figures. To appear in Int. J. Mod. Phys. D (2006).
Invited talk delivered at the 2nd International Workshop on Astronomy and
Relativistic Astrophysic
Is there a need and another way to measure the Cosmic Microwave Background temperature more accurately?
The recombination history of the Universe depends exponentially on the
temperature, T_0, of the cosmic microwave background. Therefore tiny changes of
T_0 are expected to lead to significant changes in the free electron fraction.
Here we show that even the current 1sigma-uncertainty in the value of T_0
results in more than half a percent ambiguity in the ionization history, and
more than 0.1% uncertainty in the TT and EE power spectra at small angular
scales. We discuss how the value of T_0 affects the highly redshifted
cosmological hydrogen recombination spectrum and demonstrate that T_0 could, in
principle, be measured by looking at the low frequency distortions of the
cosmic microwave background spectrum. For this no absolute measurements are
necessary, but sensitivities on the level of ~30nK are required to extract the
quasi-periodic frequency-dependent signal with typical Delta nu/nu~0.1 coming
from cosmological recombination. We also briefly mention the possibility of
obtaining additional information on the specific entropy of the Universe, and
other cosmological parameters.Comment: 4+epsilon pages, 4 Figures, accepted versio
Topology Change in Canonical Quantum Cosmology
We develop the canonical quantization of a midisuperspace model which
contains, as a subspace, a minisuperspace constituted of a
Friedman-Lema\^{\i}tre-Robertson-Walker Universe filled with homogeneous scalar
and dust fields, where the sign of the intrinsic curvature of the spacelike
hypersurfaces of homogeneity is not specified, allowing the study of topology
change in these hypersurfaces. We solve the Wheeler-DeWitt equation of the
midisuperspace model restricted to this minisuperspace subspace in the
semi-classical approximation. Adopting the conditional probability
interpretation, we find that some of the solutions present change of topology
of the homogeneous hypersurfaces. However, this result depends crucially on the
interpretation we adopt: using the usual probabilistic interpretation, we find
selection rules which forbid some of these topology changes.Comment: 23 pages, LaTex file. We added in the conclusion some comments about
path integral formalism and corrected litle misprinting
The Poisson sigma model on closed surfaces
Using methods of formal geometry, the Poisson sigma model on a closed surface
is studied in perturbation theory. The effective action, as a function on
vacua, is shown to have no quantum corrections if the surface is a torus or if
the Poisson structure is regular and unimodular (e.g., symplectic). In the case
of a Kahler structure or of a trivial Poisson structure, the partition function
on the torus is shown to be the Euler characteristic of the target; some
evidence is given for this to happen more generally. The methods of formal
geometry introduced in this paper might be applicable to other sigma models, at
least of the AKSZ type.Comment: 32 pages; references adde
Property (T) and rigidity for actions on Banach spaces
We study property (T) and the fixed point property for actions on and
other Banach spaces. We show that property (T) holds when is replaced by
(and even a subspace/quotient of ), and that in fact it is
independent of . We show that the fixed point property for
follows from property (T) when 1
. For simple Lie groups and their lattices, we prove that the fixed point property for holds for any if and only if the rank is at least two. Finally, we obtain a superrigidity result for actions of irreducible lattices in products of general groups on superreflexive Banach spaces.Comment: Many minor improvement
Human Hantavirus Infections, Sweden
The prevalent human hantavirus disease in Sweden is nephropathia epidemica, which is caused by Puumala virus and shed by infected bank voles (Clethrionomys glareolus). To evaluate temporal and spatial patterns of this disease, we studied 2,468 reported cases from a highly disease-endemic region in northern Sweden. We found that, in particular, middle-aged men living in rural dwellings near coastal areas were overrepresented. The case-patients were most often infected in late autumn, when engaged in activities near or within manmade rodent refuges. Of 862 case-patients confident about the site of virus exposure, 50% were concentrated within 5% of the study area. The incidence of nephropathia epidemica was significantly correlated with bank vole numbers within monitored rodent populations in part of the region. Understanding this relationship may help forestall future human hantavirus outbreaks
- …