6,900 research outputs found
Gravity with extra dimensions and dark matter interpretation: A straightforward approach
Any connection between dark matter and extra dimensions can be cognizably
evinced from the associated effective energy-momentum tensor. In order to
investigate and test such relationship, a higher dimensional spacetime endowed
with a factorizable general metric is regarded to derive a general expression
for the stress tensor -- from the Einstein-Hilbert action -- and to elicit the
effective gravitational potential. A particular construction for the case of
six dimensions is provided, and it is forthwith revealed that the missing mass
phenomenon may be explained, irrespective of the dark matter existence.
Moreover, the existence of extra dimensions in the universe accrues the
possibility of a straightforward mechanism for such explanation. A
configuration which density profile coincides with the Newtonian potential for
spiral galaxies is constructed, from a 4-dimensional isotropic metric plus
extra-dimensional components. A Miyamoto-Nagai \emph{ansatz} is used to solve
Einstein equations. The stable rotation curves associated to such system are
computed, in full compliance to the observational data, without fitting
techniques. The density profiles are reconstructed and compared to that ones
obtained from the Newtonian potential.Comment: 13 pages, 6 figure
Questing for Algebraic Mass Dimension One Spinor Fields
This work deals with new classes of spinors of mass dimension one in
Minkowski spacetime. In order to accomplish it, the Lounesto classification
scheme and the inversion theorem are going to be used. The algebraic framework
shall be revisited by explicating the central point performed by the Fierz
aggregate. Then the spinor classification is generalized in order to encompass
the new mass dimension one spinors. The spinor operator is shown to play a
prominent role to engender the new mass dimension one spinors, accordingly.Comment: 7 pages, final version to appear in Eur. Phys. J.
Homogeneous abundance analysis of dwarf, subgiant and giant FGK stars with and without giant planets
We have analyzed high-resolution and high signal-to-noise ratio optical
spectra of nearby FGK stars with and without detected giant planets in order to
homogeneously measure their photospheric parameters, mass, age, and the
abundances of volatile (C, N, and O) and refractory (Na, Mg, Si, Ca, Ti, V, Mn,
Fe, Ni, Cu, and Ba) elements. Our sample contains 309 stars from the solar
neighborhood (up to the distance of 100 pc), out of which 140 are dwarfs, 29
are subgiants, and 140 are giants. The photospheric parameters are derived from
the equivalent widths of Fe I and Fe II lines. Masses and ages come from the
interpolation in evolutionary tracks and isochrones on the HR diagram. The
abundance determination is based on the equivalent widths of selected atomic
lines of the refractory elements and on the spectral synthesis of C_2, CN, C I,
O I, and Na I features. We apply a set of statistical methods to analyze the
abundances derived for the three subsamples. Our results show that: i) giant
stars systematically exhibit underabundance in [C/Fe] and overabundance in
[N/Fe] and [Na/Fe] in comparison with dwarfs, a result that is normally
attributed to evolution-induced mixing processes in the envelope of evolved
stars; ii) for solar analogs only, the abundance trends with the condensation
temperature of the elements are correlated with age and anticorrelated with the
surface gravity, which is in agreement with recent studies; iii) as in the case
of [Fe/H], dwarf stars with giant planets are systematically enriched in [X/H]
for all the analyzed elements, except for O and Ba (the former due to
limitations of statistics), confirming previous findings in the literature that
not only iron has an important relation with the planetary formation; and iv)
giant planet hosts are also significantly overabundant for the same metallicity
when the elements from Mg to Cu are combined together.Comment: 20 pages, 16 figures, 8 table
On the Spinor Representation
A systematic study of the spinor representation by means of the fermionic
physical space is accomplished and implemented. The spinor representation space
is shown to be constrained by the Fierz-Pauli-Kofink identities among the
spinor bilinear covariants. A robust geometric and topological structure can be
manifested from the spinor space, wherein, for instance, the first and second
homotopy groups play prominent roles on the underlying physical properties,
associated to the fermionic fields.Comment: 16 page
False Vacuum Transitions - Analytical Solutions and Decay Rate Values
In this work we show a class of oscillating configurations for the evolution
of the domain walls in Euclidean space. The solutions are obtained
analytically. Phase transitions are achieved from the associated fluctuation
determinant, by the decay rates of the false vacuum.Comment: 6 pages, improved to match the final version to appear in EP
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