737 research outputs found
Emergent electrodynamics from the Nambu model for spontaneous Lorentz symmetry breaking
After imposing the Gauss law constraint as an initial condition upon the
Hilbert space of the Nambu model, in all its generic realizations, we recover
QED in the corresponding non-linear gauge A_{\mu}A^{\mu}=n^{2}M^{2}. Our result
is non-perturbative in the parameter M for n^{2}\neq 0 and can be extended to
the n^{2}=0 case. This shows that in the Nambu model, spontaneous Lorentz
symmetry breaking dynamically generates gauge invariance, provided the Gauss
law is imposed as an initial condition. In this way electrodynamics is
recovered, with the photon being realized as the Nambu-Goldstone modes of the
spontaneously broken symmetry, which finally turns out to be non-observableComment: 17 page
Highly charged ions: optical clocks and applications in fundamental physics
Recent developments in frequency metrology and optical clocks have been based
on electronic transitions in atoms and singly charged ions as references. These
systems have enabled relative frequency uncertainties at a level of a few parts
in . This accomplishment not only allows for extremely accurate time
and frequency measurements, but also to probe our understanding of fundamental
physics, such as variation of fundamental constants, violation of the local
Lorentz invariance, and forces beyond the Standard Model of Physics. In
addition, novel clocks are driving the development of sophisticated technical
applications. Crucial for applications of clocks in fundamental physics are a
high sensitivity to effects beyond the Standard Model and Einstein's Theory of
Relativity and a small frequency uncertainty of the clock. Highly charged ions
offer both. They have been proposed as highly accurate clocks, since they
possess optical transitions which can be extremely narrow and less sensitive to
external perturbations compared to current atomic clock species. The selection
of highly charged ions in different charge states offers narrow transitions
that are among the most sensitive ones for a change in the fine-structure
constant and the electron-to-proton mass ratio, as well as other new physics
effects. Recent advances in trapping and sympathetic cooling of highly charged
ions will in the future enable high accuracy optical spectroscopy. Progress in
calculating the properties of selected highly charged ions has allowed the
evaluation of systematic shifts and the prediction of the sensitivity to the
"new physics" effects. This article reviews the current status of theory and
experiment in the field.Comment: 53 pages, 16 figures, submitted to RM
Radiation from a dipole perpendicular to the interface between two planar semi-infinite magnetoelectric media
We consider two semi-infinite magnetoelectric media with constant dielectric
permittivity separated by a planar interface, whose electromagnetic response is
described by non-dynamical axion electrodynamics and investigate the radiation
of a point-like electric dipole located perpendicularly to the interface. We
start from the exact Green's function for the electromagnetic potential, whose
far-field approximation is obtained using a modified steepest descent
approximation. This procedure yields the standard spherical waves as well as
axially symmetric cylindrical superficial waves, which nevertheless are
restricted to a region very close to the interface. We compute the angular
distribution of the radiation and the total radiated power finding different
interference patterns, depending on the relative position dipole-observer, and
polarization mixing effects which are all absent in the standard dipole
radiation. They are a manifestation of the magnetoelectric effect induced by
axion electrodynamics. We illustrate our findings with some numerical
estimations employing realistic media as well as some hypothetical choices in
order to illuminate the effects of the magnetoelectric coupling which is
usually very small.Comment: 29 pages, 18 figures, new references added, results unchanged,
improved explanations, matches accepted version in Rev. Mex. Fi
The stellar, molecular gas and dust content of the host galaxies of two z~2.8 dust obscured quasars
We present optical through radio observations of the host galaxies of two
dust obscured, luminous quasars selected in the mid-infrared, at z=2.62 and
z=2.99, including a search for CO emission. Our limits on the CO luminosities
are consistent with these objects having masses of molecular gas <~10^10 solar
masses, several times less than those of luminous submillimeter-detected
galaxies (SMGs) at comparable redshifts. Their near-infrared spectral energy
distributions, however, imply that these galaxies have high stellar masses
(~10^11-12 solar masses). The relatively small reservoirs of molecular gas and
low dust masses are consistent with them being relatively mature systems at
high-z.Comment: AJ, in pres
The Spitzer mid-infrared AGN survey. II-the demographics and cosmic evolution of the AGN population
We present luminosity functions derived from a spectroscopic survey of AGN
selected from Spitzer Space Telescope imaging surveys. Selection in the
mid-infrared is significantly less affected by dust obscuration. We can thus
compare the luminosity functions of the obscured and unobscured AGN in a more
reliable fashion than by using optical or X-ray data alone. We find that the
AGN luminosity function can be well described by a broken power-law model in
which the break luminosity decreases with redshift. At high redshifts
(), we find significantly more AGN at a given bolometric luminosity than
found by either optical quasar surveys or hard X-ray surveys. The fraction of
obscured AGN decreases rapidly with increasing AGN luminosity, but, at least at
high redshifts, appears to remain at \% even at bolometric
luminosities . The data support a picture in which the
obscured and unobscured populations evolve differently, with some evidence that
high luminosity obscured quasars peak in space density at a higher redshift
than their unobscured counterparts. The amount of accretion energy in the
Universe estimated from this work suggests that AGN contribute about 12\% to
the total radiation intensity of the Universe, and a high radiative accretion
efficiency is required to match current
estimates of the local mass density in black holes.Comment: 14 pages, accepted by Ap
Spectral energy distributions of quasars selected in the mid-infrared
We present preliminary results on fitting of SEDs to 142 z>1 quasars selected
in the mid-infrared. Our quasar selection finds objects ranging in extinction
from highly obscured, type-2 quasars, through more lightly reddened type-1
quasars and normal type-1s. We find a weak tendency for the objects with the
highest far-infrared emission to be obscured quasars, but no bulk systematic
offset between the far-infrared properties of dusty and normal quasars as might
be expected in the most naive evolutionary schemes. The hosts of the type-2
quasars have stellar masses comparable to those of radio galaxies at similar
redshifts. Many of the type-1s, and possibly one of the type-2s require a very
hot dust component in addition to the normal torus emission.Comment: 4 pages, 2 figures, to appear in the proceedings of The Spectral
Energy Distribution of Galaxies, Preston, September 2011, eds R.J. Tuffs &
C.C. Popesc
Decay rate measurement of the first vibrationally excited state of MgH in a cryogenic Paul trap
We present a method to measure the decay rate of the first excited
vibrational state of simple polar molecular ions being part of a Coulomb
crystal in a cryogenic linear Paul trap. Specifically, we have monitored the
decay of the == towards the ==
level in MgH by saturated laser excitation of the ==-== transition followed by state selective
resonance enhanced two-photon dissociation out of the == level. The technique enables the determination of decay rates, and
thus absorption strengths, with an accuracy at the few percent level.Comment: 5 pages, 4 figure
Explicit spacetime symmetry breaking in matter: the reversed Vavilov-\v{C}erenkov radiation
We show that reversed Vavilov-\v{C}erenkov radiation occurs simultaneously
with the forward output in naturally existing materials when an electric charge
moves with a constant velocity perpendicular to the planar interface between
two magnetoelectric media. Using the Green's function in the far-field
approximation we calculate the angular distribution of the radiated energy per
unit frequency obtaining a non-zero contribution in the backward direction.Comment: Four pages, 1 figure, tex, ws-procs9x6-cpt19.cls, Presented at the
Eighth Meeting on CPT and Lorentz Symmetry, Bloomington, Indiana, May 12-16,
2019, typos correcte
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