23,321 research outputs found
Is it possible to accommodate massive photons in the framework of a gauge-invariant electrodynamics?
The construction of an alternative electromagnetic theory that preserves
Lorentz and gauge symmetries, is considered. We start off by building up
Maxwell electrodynamics in (3+1)D from the assumption that the associated
Lagrangian is a gauge-invariant functional that depends on the electron and
photon fields and their first derivatives only. In this scenario, as
well-known, it is not possible to set up a Lorentz invariant gauge theory
containing a massive photon. We show nevertheless that there exist two
radically different electrodynamics, namely, the Chern-Simons and the Podolsky
formulations, in which this problem can be overcome. The former is only valid
in odd space-time dimensions, while the latter requires the presence of
higher-order derivatives of the gauge field in the Lagrangian. This theory,
usually known as Podolsky electrodynamics, is simultaneously gauge and Lorentz
invariant; in addition, it contains a massive photon. Therefore, a massive
photon, unlike the popular belief, can be adequately accommodated within the
context of a gauge-invariant electrodynamics.Comment: 10 page
Calcium Triplet Synthesis
We present theoretical equivalent widths for the sum of the two strongest
lines of the Calcium Triplet, CaT index, in the near-IR, using evolutionary
techniques and the most recent models and observational data for this feature
in individual stars. We compute the CaT index for Single Stellar Populations
(instantaneous burst, standard Salpeter-type IMF) at four metallicities,
Z=0.004, 0.008, 0.02 (solar) and 0.05, and ranging in age from very young
bursts of star formation (few Myr) to old stellar populations, up to 17 gyr,
representative of globular clusters, elliptical galaxies and bulges of spirals.
The interpretation of the observed equivalent widths of CaT in different
stellar systems is discussed. Composite-population models are also computed as
a tool to interpret the CaT detections in star-forming regions, in order to
disantangle between the component due to Red Supergiants stars, RSG, and the
underlying, older, population. CaT is found to be an excellent
metallicity-indicator for populations older than 1 Gyr, practically independent
of the age. We discuss its application to remove the age- metallicity
degeneracy, characteristic of all studies of galaxy evolution based on the
usual integrated indices (both broad band colors and narrow band indices). The
application of the models computed here to the analysis of a sample of
elliptical galaxies will be discussed in a forthcoming paper (Gorgas et al.
1998).Comment: 17 pages, 7 figures, to be published in A&
Topologically stable gapped state in a layered superconductor
We show that a layered superconductor, described by a two-component order
parameter, has a gapped state above the ground state, topologically protected
from decay, containing flow and counter flow in the absence of an applied
magnetic field. This state is made of skyrmions, breaks time reversal symmetry
and produces a weak local magnetic field below the present threshold of
detection by SR and NMR/NQR. We estimate the density of carriers that
condense into the pseudogap.Comment: 6 pages, 4 figure
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