115 research outputs found
Isotropy theorem for cosmological Yang-Mills theories
We consider homogeneous non-abelian vector fields with general potential
terms in an expanding universe. We find a mechanical analogy with a system of N
interacting particles (with N the dimension of the gauge group) moving in three
dimensions under the action of a central potential. In the case of bounded and
rapid evolution compared to the rate of expansion, we show by making use of a
generalization of the virial theorem that for arbitrary potential and
polarization pattern, the average energy-momentum tensor is always diagonal and
isotropic despite the intrinsic anisotropic evolution of the vector field. We
consider also the case in which a gauge-fixing term is introduced in the action
and show that the average equation of state does not depend on such a term.
Finally, we extend the results to arbitrary background geometries and show that
the average energy-momentum tensor of a rapidly evolving Yang-Mills fields is
always isotropic and has the perfect fluid form for any locally inertial
observer.Comment: 8 pages, 3 figure
Isotropy theorem for arbitrary-spin cosmological fields
We show that the energy-momentum tensor of homogeneous fields of arbitrary
spin in an expanding universe is always isotropic in average provided the
fields remain bounded and evolve rapidly compared to the rate of expansion. An
analytic expression for the average equation of state is obtained for
Lagrangians with generic power-law kinetic and potential terms. As an example
we consider the behavior of a spin-two field in the standard Fierz-Pauli theory
of massive gravity. The results can be extended to general space-time
geometries for locally inertial observers.Comment: 4 pages, 0 figures. Published on JCA
Cosmological perturbations in coherent oscillating scalar field models
The fact that fast oscillating homogeneous scalar fields behave as perfect
fluids in average and their intrinsic isotropy have made these models very
fruitful in cosmology. In this work we will analyse the perturbations dynamics
in these theories assuming general power law potentials . At leading order in the wavenumber expansion, a simple
expression for the effective sound speed of perturbations is obtained
with the effective equation of
state. We also obtain the first order correction in
, when the wavenumber of the perturbations is
much smaller than the background oscillation frequency, .
For the standard massive case we have also analysed general anharmonic
contributions to the effective sound speed. These results are reached through a
perturbed version of the generalized virial theorem and also studying the exact
system both in the super-Hubble limit, deriving the natural ansatz for
; and for sub-Hubble modes, exploiting Floquet's theorem.Comment: 13 pages, 6 figures. Published on JHE
Altered electrochemistry of poly(3,4-ethylenedioxythiophene) after activation of the inserted cobalt ions
Cobalt ions were inserted into poly(3,4-ethylenedioxythiophene) by cyclic voltammetry in a 0.1M Co(NO3)2 aqueous solution (PEDOT(Co)). After activation of the inserted cobalt, the PEDOT(aCo) system was investigated by cyclic voltammetry, digital video electrochemistry, spectroelectrogravimetry, and coupled impedance techniques (ac-electrogravimetry) to elucidate the key role of inserted cobalt ions in the altered electrochemistry of PEDOT. The incorporation of Co2+ involves slow transfer of cations for charge compensation during 2+⇄3+ conversion inside the PEDOT. This fact explains the enhanced charge storage showed by PEDOT(aCo) compared with pristine PEDOT at similar potentials. Finally, the stability of PEDOT(aCo) was investigated by cyclic voltammetry measuring at the same time current, mass and motional resistance variation during 100 cycles offering high stability at all times.This work was supported by the Spanish E3TECH-PLUS Research Network RED2022-134552-T (MICINN/AEI, Spain). SEM was carried out in the Microscopy Section of Central Service for Experimental Research (SCSIE) of the University of Valencia. Esteban Guillén acknowledges the support from the Generalitat Valenciana (INVEST/2022/431)
Constraints on anharmonic corrections of Fuzzy Dark Matter
The cold dark matter (CDM) scenario has proved successful in cosmology.
However, we lack a fundamental understanding of its microscopic nature.
Moreover, the apparent disagreement between CDM predictions and
subgalactic-structure observations has prompted the debate about its behaviour
at small scales. These problems could be alleviated if the dark matter is
composed of ultralight fields , usually known as
fuzzy dark matter (FDM). Some specific models, with axion-like potentials, have
been thoroughly studied and are collectively referred to as ultralight axions
(ULAs) or axion-like particles (ALPs). In this work we consider anharmonic
corrections to the mass term coming from a repulsive quartic self-interaction.
Whenever this anharmonic term dominates, the field behaves as radiation instead
of cold matter, modifying the time of matter-radiation equality. Additionally,
even for high masses, i.e. masses that reproduce the cold matter behaviour, the
presence of anharmonic terms introduce a cut-off in the matter power spectrum
through its contribution to the sound speed. We analyze the model and derive
constraints using a modified version of CLASS and comparing with CMB and
large-scale structure data.Comment: 14 pages, 7 figure
Avian predators as a biological control system of common vole (Microtus arvalis) populations in NW Spain: experimental set-up and preliminary results
Jareño, D., Paz, A., Arroyo, L., Viñuela, J., Arroyo, B.E., Mougeot, F., Luque-Larena, J.J., Fargallo, J.A
Limits on Associated Production of Visibly and Invisibly Decaying Higgs Bosons from Z Decays
Many extensions of the standard electroweak model Higgs sector suggest that
the main Higgs decay channel is "invisible", for example, where
denotes the majoron, a weakly interacting pseudoscalar Goldstone boson
associated to the spontaneous violation of lepton number. In many of these
models the Higgs boson may also be produced in association to a massive
pseudoscalar boson (HA), in addition to the standard Bjorken mechanism (HZ). We
describe a general strategy to determine limits from LEP data on the masses and
couplings of such Higgs bosons, using the existing data on acoplanar dijet
events as well as data on four and six jet event topologies. For the sake
of illustration, we present constraints that can be obtained for the ALEPH
data.Comment: FTUV/94-36, IFIC/94-31 TIFR/TH/94--25, 12 pages + 4 figures (included
as ps files at the end
- …