51,660 research outputs found
Effective Geometry
We introduce the concept of effective geometry by studying several systems in
which it arises naturally. As an example of the power and conciseness of the
method, it is shown that a flowing dielectric medium with a linear response to
an external electric field can be used to generate an analog geometry that has
many of the formal properties of a \Sch black hole for light rays, in spite of
birefringence. The surface gravity of this analog black hole has a contribution
that depends only on the dielectric properties of the fluid (in addition to the
usual term dependent on the acceleration). This term may be give a hint to a
new mechanism to increase the temperature of Hawking radiation.Comment: 13 pages, RevTex4, Contribution to the Proceedings of the Xth
Brazilian School of Gravitation and Cosmology, to be published by AI
Coherent States of Accelerated Relativistic Quantum Particles, Vacuum Radiation and the Spontaneous Breakdown of the Conformal SU(2,2) Symmetry
We give a quantum mechanical description of accelerated relativistic
particles in the framework of Coherent States (CS) of the (3+1)-dimensional
conformal group SU(2,2), with the role of accelerations played by special
conformal transformations and with the role of (proper) time translations
played by dilations. The accelerated ground state of first
quantization is a CS of the conformal group. We compute the distribution
function giving the occupation number of each energy level in
and, with it, the partition function Z, mean energy E and entropy S, which
resemble that of an "Einstein Solid". An effective temperature T can be
assigned to this "accelerated ensemble" through the thermodynamic expression
dE/dS, which leads to a (non linear) relation between acceleration and
temperature different from Unruh's (linear) formula. Then we construct the
corresponding conformal-SU(2,2)-invariant second quantized theory and its
spontaneous breakdown when selecting Poincar\'e-invariant degenerated
\theta-vacua (namely, coherent states of conformal zero modes). Special
conformal transformations (accelerations) destabilize the Poincar\'e vacuum and
make it to radiate.Comment: 25 pages, LaTeX, 3 figures. Additional information (resulting in four
extra pages) and a slight change of focus has been introduced in order to
make the line of arguments more clear. Title changed accordingl
Physics at high Q^2 and p^2_t: Summary of DIS 2000
We summarize the experimental and theoretical results presented in the
"Physics at the Highest Q^2 and p^2_t" working group at the DIS 2000 Workshop.
High Q^2 and p^2_t processes measured at current and future colliders allow to
improve our knowledge of Standard Model (SM) physics, by providing precise
measurements of the SM parameters and, consequently, consistency checks of the
SM. Moreover, they give information on key quantities for the calculation of
the SM expectations in a yet unexplored domain, such as the parton densities of
the proton or the photon. In addition to these experimental inputs,
higher-order calculations are also needed to obtain precise expectations for SM
processes, which are a key ingredient for the searches for new phenomena in
high Q^2 and p^2_t processes at current and future experiments. The
experimental and theoretical status of SM physics at high Q^2 and p^2_t is
reviewed in the first part of this summary, with the remaining being dedicated
to physics beyond the Standard Model.Comment: 17 pages, 10 figures. Typos correcte
VLT and GTC observations of SDSS J0123+00: a type 2 quasar triggered in a galaxy encounter?
We present long-slit spectroscopy, continuum and [OIII]5007 imaging data
obtained with the Very Large Telescope and the Gran Telescopio Canarias of the
type 2 quasar SDSS J0123+00 at z=0.399. The quasar lies in a complex, gas-rich
environment. It appears to be physically connected by a tidal bridge to another
galaxy at a projected distance of ~100 kpc, which suggests this is an
interacting system. Ionized gas is detected to a distance of at least ~133 kpc
from the nucleus. The nebula has a total extension of ~180 kpc. This is one of
the largest ionized nebulae ever detected associated with an active galaxy.
Based on the environmental properties, we propose that the origin of the nebula
is tidal debris from a galactic encounter, which could as well be the
triggering mechanism of the nuclear activity. SDSS J0123+00 demonstrates that
giant, luminous ionized nebulae can exist associated with type 2 quasars of low
radio luminosities, contrary to expectations based on type 1 quasar studies.Comment: 6 pages, 5 figures. Accepted for publication in MNRAS Letter
- …