596 research outputs found
Boundary Conditions for Topological Quantum Field Theories, Anomalies and Projective Modular Functors
We study boundary conditions for extended topological quantum field theories
(TQFTs) and their relation to topological anomalies. We introduce the notion of
TQFTs with moduli level , and describe extended anomalous theories as
natural transformations of invertible field theories of this type. We show how
in such a framework anomalous theories give rise naturally to homotopy fixed
points for -characters on -groups. By using dimensional reduction on
manifolds with boundaries, we show how boundary conditions for
-dimensional TQFTs produce -dimensional anomalous field theories.
Finally, we analyse the case of fully extended TQFTs, and show that any fully
extended anomalous theory produces a suitable boundary condition for the
anomaly field theory.Comment: 26 pages, 6 figures. Exposition improved, bibliography updated. Final
version, to appear in Comm. Math. Phy
Planck constraints on neutrino isocurvature density perturbations
The recent Cosmic Microwave Background data from the Planck satellite
experiment, when combined with HST determinations of the Hubble constant, are
compatible with a larger, non-standard, number of relativistic degrees of
freedom at recombination, parametrized by the neutrino effective number
. In the curvaton scenario, a larger value for could arise
from a non-zero neutrino chemical potential connected to residual neutrino
isocurvature density (NID) perturbations after the decay of the curvaton field,
parametrized by the amplitude . Here we present new constraints
on and from an analysis of recent cosmological data.
We found that the Planck+WP dataset does not show any indication for a neutrino
isocurvature component, severly constraining its amplitude, and that current
indications for a non-standard are further relaxed.Comment: 5 pages, 3 figure
First cosmological constraints combining Planck with the recent gravitational-wave standard siren measurement of the Hubble constant
The recent observations of gravitational-wave and electromagnetic emission
produced by the merger of the binary neutron-star system GW170817 have opened
the possibility of using standard sirens to constrain the value of the Hubble
constant. While the reported bound of at C.L. is
significantly weaker than those recently derived by observations of Cepheid
variables, it does not require any form of cosmic distance ladder and can be
considered as complementary and, in principle, more conservative. Here we
combine, for the first time, the new measurement with the Planck Cosmic
Microwave Background observations in a parameters extended CDM
scenario, where the Hubble constant is weakly constrained from CMB data alone
and bound to a low value km/s/Mpc at C.L. We point
out that the non-Gaussian shape of the GW170817 bound makes lower values of the
Hubble constant in worst agreement with observations than what expected from a
Gaussian form. The inclusion of the new GW170817 Hubble constant measurement
therefore significantly reduces the allowed parameter space, improving the
cosmological bounds on several parameters as the neutrino mass, curvature and
the dark energy equation of state.Comment: 5 pages, 4 Figures, few typos correcte
Frobenius algebras and homotopy fixed points of group actions on bicategories
We explicitly show that symmetric Frobenius structures on a
finite-dimensional, semi-simple algebra stand in bijection to homotopy fixed
points of the trivial SO(2)-action on the bicategory of finite-dimensional,
semi-simple algebras, bimodules and intertwiners. The results are motivated by
the 2-dimensional Cobordism Hypothesis for oriented manifolds, and can hence be
interpreted in the realm of Topological Quantum Field Theory.Comment: 19 pages, published in TA
Can interacting dark energy solve the tension?
The answer is Yes! We indeed find that interacting dark energy can alleviate
the current tension on the value of the Hubble constant between the
Cosmic Microwave Background anisotropies constraints obtained from the Planck
satellite and the recent direct measurements reported by Riess et al. 2016. The
combination of these two datasets points towards an evidence for a non-zero
dark matter-dark energy coupling at more than two standard deviations,
with at CL. However the tension is
better solved when the equation of state of the interacting dark energy
component is allowed to freely vary, with a phantom-like equation of state
(at CL), ruling out the pure cosmological constant
case, , again at more than two standard deviations. When Planck data are
combined with external datasets, as BAO, JLA Supernovae Ia luminosity
distances, cosmic shear or lensing data, we find good consistency with the
cosmological constant scenario and no compelling evidence for a dark
matter-dark energy coupling.Comment: 10 pages, 6 figure
Reconciling Planck with the local value of in extended parameter space
The recent determination of the local value of the Hubble constant by Riess
et al, 2016 (hereafter R16) is now 3.3 sigma higher than the value derived from
the most recent CMB anisotropy data provided by the Planck satellite in a LCDM
model. Here we perform a combined analysis of the Planck and R16 results in an
extended parameter space, varying simultaneously 12 cosmological parameters
instead of the usual 6. We find that a phantom-like dark energy component, with
effective equation of state at 68 % c.l. can solve
the current tension between the Planck dataset and the R16 prior in an extended
CDM scenario. On the other hand, the neutrino effective number is
fully compatible with standard expectations. This result is confirmed when
including cosmic shear data from the CFHTLenS survey and CMB lensing
constraints from Planck. However, when BAO measurements are included we find
that some of the tension with R16 remains, as also is the case when we include
the supernova type Ia luminosity distances from the JLA catalog.Comment: 6 pages, 1 figur
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