419 research outputs found
Constrained Dynamics of Tachyon Field in FRWL Spacetime
In this paper we continue study of tachyon scalar field described by a
Dirac-Born-Infeld (DBI) type action with constraints in the cosmological
context. The proposed extension of the system introducing an auxiliary field in
the minisuperspace framework is discussed. A new equivalent set of constraints
is constructed, satisfying the usual regularity conditions.Comment: 10 pages, to be published in the Special Issue of the Facta
Universitatis Series: Physics, Chemistry and Technology devoted to the
SEENET-MTP Balkan Workshop BSW2019 (3-14 June 2018, Nis, Serbia
A symmetry invariant integral on kappa-deformed spacetime
In this note we present an approach using both constructive and Hopf
algebraic methods to contribute to the not yet fully satisfactory definition of
an integral on kappa-deformed spacetime. The integral presented here is based
on the inner product of differential forms and it is shown that this integral
is explicitly invariant under the deformed symmetry structure.Comment: 16 page
CONSTRAINED DYNAMICS OF TACHYON FIELD IN FRWL SPACETIME
In this paper, we continue the study of tachyon scalar field described by a Dirac-Born-Infeld (DBI) type action with constraints in the cosmological context. The proposed extension of the system introducing an auxiliary field in the minisuperspace framework is discussed. A new equivalent set of constraints is constructed, satisfying the usual regularity conditions
AdS-inspired noncommutative gravity on the Moyal plane
We consider noncommutative gravity on a space with canonical noncommutativity
that is based on the commutative MacDowell-Mansouri action. Gravity is treated
as gauge theory of the noncommutative group and the
Seiberg-Witten (SW) map is used to express noncommutative fields in terms of
the corresponding commutative fields. In the commutative limit the
noncommutative action reduces to the Einstein-Hilbert action plus the
cosmological term and the topological Gauss-Bonnet term. After the SW expansion
in the noncommutative parameter the first order correction to the action, as
expected, vanishes. We calculate the second order correction and write it in a
manifestly gauge covariant way.Comment: 22 pages, no figures, final versio
A new model for the structure of the DACs and SACs regions in the Oe and Be stellar atmospheres
In this paper we present a new mathematical model for the density regions
where a specific spectral line and its SACs/DACs are created in the Oe and Be
stellar atmospheres. In the calculations of final spectral line function we
consider that the main reasons of the line broadening are the rotation of the
density regions creating the spectral line and its DACs/SACs, as well as the
random motions of the ions. This line function is able to reproduce the
spectral feature and it enables us to calculate some important physical
parameters, such as the rotational, the radial and the random velocities, the
Full Width at Half Maximum, the Gaussian deviation, the optical depth, the
column density and the absorbed or emitted energy. Additionally, we can
calculate the percentage of the contribution of the rotational velocity and the
ions' random motions of the DACs/SACs regions to the line broadening. Finally,
we present two tests and three short applications of the proposed model.Comment: 9 pages, 5 figures, accepted for publication in PAS
Differential algebras on kappa-Minkowski space and action of the Lorentz algebra
We propose two families of differential algebras of classical dimension on
kappa-Minkowski space. The algebras are constructed using realizations of the
generators as formal power series in a Weyl super-algebra. We also propose a
novel realization of the Lorentz algebra so(1,n-1) in terms of Grassmann-type
variables. Using this realization we construct an action of so(1,n-1) on the
two families of algebras. Restriction of the action to kappa-Minkowski space is
covariant. In contrast to the standard approach the action is not Lorentz
covariant except on constant one-forms, but it does not require an extra
cotangent direction.Comment: 16 page
Differential structure on kappa-Minkowski space, and kappa-Poincare algebra
We construct realizations of the generators of the -Minkowski space
and -Poincar\'{e} algebra as formal power series in the -adic
extension of the Weyl algebra. The Hopf algebra structure of the
-Poincar\'{e} algebra related to different realizations is given. We
construct realizations of the exterior derivative and one-forms, and define a
differential calculus on -Minkowski space which is compatible with the
action of the Lorentz algebra. In contrast to the conventional bicovariant
calculus, the space of one-forms has the same dimension as the
-Minkowski space.Comment: 20 pages. Accepted for publication in International Journal of Modern
Physics
Non-LTE calculations for neutral Na in late-type stars using improved atomic data
Neutral sodium is a minority species in the atmospheres of late-type stars,
and line formation in local thermodynamic equilibrium (LTE) is often a poor
assumption, in particular for strong lines. We present an extensive grid of
non-LTE calculations for several NaI lines in cool stellar atmospheres,
including metal-rich and metal-poor dwarfs and giants. For the first time, we
constructed a Na model atom that incorporates accurate quantum mechanical
calculations for collisional excitation and ionisation by electrons as well as
collisional excitation and charge exchange reactions with neutral hydrogen.
Similar to LiI, the new rates for hydrogen impact excitation do not affect the
statistical equilibrium calculations, while charge exchange reactions have a
small but non-negligible influence. The presented LTE and non-LTE
curves-of-growth can be interpolated to obtain non-LTE abundances and abundance
corrections for arbitrary stellar parameter combinations and line strengths.
The typical corrections for weak lines are -0.1...-0.2dex, whereas saturated
lines may overestimate the abundance in LTE by more than 0.5dex. The non-LTE Na
abundances appear very robust with respect to uncertainties in the input
collisional data.Comment: 9 pages, 8 figures, accepted for publication in A&
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