921 research outputs found
Thermodynamical aspects of running vacuum models
The thermal history of a large class of running vacuum models in which the
effective cosmological term is described by a truncated power series of the
Hubble rate, whose dominant term is , is discussed
in detail. Specifically, by assuming that the ultra-relativistic particles
produced by the vacuum decay emerge into space-time in such a way that its
energy density , the temperature evolution law and the
increasing entropy function are analytically calculated. For the whole class of
vacuum models explored here we findthat the primeval value of the comoving
radiation entropy density (associated to effectively massless particles) starts
from zero and evolves extremely fast until reaching a maximum near the end of
the vacuum decay phase, where it saturates. The late time conservation of the
radiation entropy during the adiabatic FRW phase also guarantees that the whole
class of running vacuum models predicts thesame correct value of the present
day entropy, (in natural units), independently of the
initial conditions. In addition, by assuming Gibbons-Hawking temperature as an
initial condition, we find that the ratio between the late time and primordial
vacuum energy densities is in agreement with naive estimates from quantum field
theory, namely, . Such results
are independent on the power and suggests that the observed Universe may
evolve smoothly between two extreme, unstable, nonsingular de Sitter phases.Comment: 15 pages in free style, 2 figures, to appear in European Phys.
Journal C.,(this work generalizes that of arXiv:1412.5196
Conflict resolution in Western Sahara
This paper examines the democratisation agenda laid out by Western governments for the North African region vis-Ă -vis their Realpolitik conflict containment approach towards the Western Sahara conflict. Western policymakers conceive the United Nations Mission for the Referendum in Western Sahara as a safety net that contains tension in the region and enables geo-strategic and economic partnerships with Algeria and Morocco. This paper underlines that the international community could play a greater role in promoting the long-term stability of the North African region by pursuing innovative policies geared towards addressing the root causes of the Western Sahara conflict
Relaxing a large cosmological constant in the astrophysical domain
We study the problem of relaxing a large cosmological constant in the
astrophysical domain through a dynamical mechanism based on a modified action
of gravity previously considered by us at the cosmological level. We solve the
model in the Schwarzschild-de Sitter metric for large and small astrophysical
scales, and address its physical interpretation by separately studying the
Jordan's frame and Einstein's frame formulations of it. In particular, we
determine the extremely weak strength of fifth forces in our model and show
that they are virtually unobservable. Finally, we estimate the influence that
the relaxation mechanism may have on pulling apart the values of the two
gravitational potentials Psi and Phi of the metric, as this implies a departure
of the model from General Relativity and could eventually provide an
observational test of the new framework at large astrophysical scales, e.g.
through gravitational lensing.Comment: 14 pages, 3 figures, accepted in Mod. Phys. Lett. A, extended
discussion, references adde
Supersymmetric effects on heavy charged Higgs boson production in hadron colliders
The production of a heavy supersymmetric charged Higgs boson (M_{H^{\pm}}> 200 GeV) at the Tevatron and at the LHC is studied. We include the leading one-loop quantum effects within the MSSM in the relevant high \tan\beta region. Whereas the chances for the Tevatron are limited, and critically depend on the size of the unknown NLO QCD effects, at the LHC the discovery range is more comfortable and may extend the reach above M_{H^{\pm}}= 1 TeV
Higgs triplet effects in purely leptonic processes
We consider the effect of complex Higgs triplets on purely leptonic processes
and survey the experimental constraints on the mass and couplings of their
single and double charge members. Present day experiments tolerate values of
the Yukawa couplings of these scalars at the level of the standard electroweak
gauge couplings. We show that the proposed measurement of the ratio
R_{LCD}=\sigma (\nu_{\mu}e)/ [\sigma (\bb\nu_{\mu}e) + \sigma (\nu_e e )]
would allow to explore a large region of the parameter space inaccessible to
the usual ratio R=\sigma (\nu_{\mu}e)/\sigma (\bb\nu_{\mu}e).Comment: 14 pages, LaTeX, Three figures included using uufiles. A postscript
version is available at ftp://ftp.ifae.es/preprint/ft/uabft378.p
Why 1,2âquinone derivatives are more stable than their 2,3âanalogues?
In this work, we have studied the relative stability
of 1,2- and 2,3-quinones. While 1,2-quinones have
a closed-shell singlet ground state, the ground state for
the studied 2,3-isomers is open-shell singlet, except for
2,3-naphthaquinone that has a closed-shell singlet ground
state. In all cases, 1,2-quinones are more stable than their
2,3-counterparts. We analyzed the reasons for the higher
stability of the 1,2-isomers through energy decomposition
analysis in the framework of KohnâSham molecular orbital
theory. The results showed that we have to trace the origin
of 1,2-quinonesâ enhanced stability to the more efficient
bonding in the Ï-electron system due to more favorable
overlap between the SOMOÏ of the ·C4nâ2H2nâCH·· and
··CHâCOâCO· fragments in the 1,2-arrangement. Furthermore,
whereas 1,2-quinones present a constant trend with their elongation for all analyzed properties (geometric,
energetic, and electronic), 2,3-quinone derivatives present a
substantial breaking in monotonicity.European
Union in the framework of European Social Fund through the Warsaw
University of Technology Development Programme. O.A. S., H.
S. and T.M. K
Cosmology with variable parameters and effective equation of state for Dark Energy
A cosmological constant, Lambda, is the most natural candidate to explain the
origin of the dark energy (DE) component in the Universe. However, due to
experimental evidence that the equation of state (EOS) of the DE could be
evolving with time/redshift (including the possibility that it might behave
phantom-like near our time) has led theorists to emphasize that there might be
a dynamical field (or some suitable combination of them) that could explain the
behavior of the DE. While this is of course one possibility, here we show that
there is no imperative need to invoke such dynamical fields and that a variable
cosmological constant (including perhaps a variable Newton's constant too) may
account in a natural way for all these features.Comment: LaTeX, 9 pages, 1 figure. Talk given at the 7th Intern. Workshop on
Quantum Field Theory Under the Influence of External Conditions (QFEXT 05
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