2,251 research outputs found
Friedmann model with viscous cosmology in modified gravity theory
In this paper, we introduce bulk viscosity in the formalism of modified
gravity theory in which the gravitational action contains a general function
, where and denote the curvature scalar and the trace of the
energy-momentum tensor, respectively within the framework of a flat
Friedmann-Robertson-Walker model. As an equation of state for prefect fluid, we
take , where and viscous term as a
bulk viscosity due to isotropic model, of the form , where and are constants, and
is the Hubble parameter. The exact non-singular solutions to the
corresponding field equations are obtained with non- viscous and viscous
fluids, respectively by assuming a simplest particular model of the form of
, where ( is a constant). A big-rip
singularity is also observed for at a finite value of cosmic time
under certain constraints. We study all possible scenarios with the possible
positive and negative ranges of to analyze the expansion history of
the universe. It is observed that the universe accelerates or exhibits
transition from decelerated phase to accelerated phase under certain
constraints of and . We compare the viscous models with the
non-viscous one through the graph plotted between scale factor and cosmic time
and find that bulk viscosity plays the major role in the expansion of the
universe. A similar graph is plotted for deceleration parameter with
non-viscous and viscous fluids and find a transition from decelerated to
accelerated phase with some form of bulk viscosity.Comment: 19 pages, 3 figures, the whole paper has been revised to improve the
quality of paper. Some references added. arXiv admin note: text overlap with
arXiv:1307.4262 by other author
Radiative and Seesaw Threshold Corrections to the Symmetric Neutrino Mass Matrix
We systematically analyze the radiative corrections to the symmetric
neutrino mass matrix at high energy scale, say the GUT scale, in the charged
lepton basis. There are significant corrections to the neutrino parameters both
in the Standard Model (SM) and Minimal Supersymmetric Standard Model (MSSM)
with large tan, when the renormalization group evolution (RGE) and
seesaw threshold effects are taken into consideration. We find that in the SM
all three mixing angles and atmospheric mass squared difference are
simultaneously obtained in their current 3 ranges at the electroweak
scale. However, the solar mass squared difference is found to be larger than
its allowed 3 range at the low scale in this case. There are
significant contributions to neutrino masses and mixing angles in the MSSM with
large tan from the RGEs even in the absence of seesaw threshold
corrections. However, we find that the mass squared differences and the mixing
angles are obtained in their current 3 ranges at low energy when the
seesaw threshold effects are also taken into account in the MSSM with large
tan.Comment: 20 Pages, 2 Figures and 2 Table
Labour productivity in state-owned enterprises
In the aftermath of the Global and Financial Crisis (GFC), between 2013 and 2015, the Portuguese government revoked four holidays for both public sector and private employees. We test whether the revocation had an effect on labour productivity in State-Owned Enterprises (SOEs) in Portugal. Moreover, we also study whether such effects are different taking into account the SOEs managed by the Central Government or the Local and Regional Governments. Our results show that revocation of holidays did not impact labour productivity for either central or local and regional government managed SOEs. Though revocation of holidays espoused to improve productivity, the policy seems to have served a ceremonial purpose, but not an economic oneinfo:eu-repo/semantics/publishedVersio
Multi-wavelength Temporal Variability of the Blazar 3C 454.3 during 2014 Activity Phase
We present a multi-wavelength temporal analysis of the blazar 3C 454.3 during
the high -ray active period from May-December, 2014. Except for X-rays,
the period is well sampled at near-infrared (NIR)-optical by the \emph{SMARTS}
facility and the source is detected continuously on daily timescale in the
\emph{Fermi}-LAT -ray band. The source exhibits diverse levels of
variability with many flaring/active states in the continuously sampled
-ray light curve which are also reflected in the NIR-optical light
curves and the sparsely sampled X-ray light curve by the \emph{Swift}-XRT.
Multi-band correlation analysis of this continuous segment during different
activity periods shows a change of state from no lags between IR and
-ray, optical and -ray, and IR and optical to a state where
-ray lags the IR/optical by 3 days. The results are consistent
with the previous studies of the same during various -ray flaring and
active episodes of the source. This consistency, in turn, suggests an extended
localized emission region with almost similar conditions during various
-ray activity states. On the other hand, the delay of -ray with
respect to IR/optical and a trend similar to IR/optical in X-rays along with
strong broadband correlations favor magnetic field related origin with X-ray
and -ray being inverse Comptonized of IR/optical photons and external
radiation field, respectively.Comment: 15 pages, 5 figures, 1 table, MNRAS accepte
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