355 research outputs found
Vacuum energy and cosmological evolution
An expanding universe is not expected to have a static vacuum energy density.
The so-called cosmological constant should be an approximation,
certainly a good one for a fraction of a Hubble time, but it is most likely a
temporary description of a true dynamical vacuum energy variable that is
evolving from the inflationary epoch to the present day. We can compare the
evolving vacuum energy with a Casimir device where the parallel plates slowly
move apart ("expand"). The total vacuum energy density cannot be measured, only
the effect associated to the presence of the plates, and then also their
increasing separation with time. In the universe there is a nonvanishing
spacetime curvature as compared to Minkowskian spacetime that is changing
with the expansion. The vacuum energy density must change accordingly, and we
naturally expect . A class of dynamical vacuum
models that trace such rate of change can be constructed. They are compatible
with the current cosmological data, and conveniently extended can account for
the complete cosmic evolution from the inflationary epoch till the present
days. These models are very close to the CDM model for the late
universe, but very different from it at the early times. Traces of the inherent
vacuum dynamics could be detectable in our recent past.Comment: Slightly extended discussion, typos corrected and references adde
The Top-Quark Width in the Light of -Boson Physics
We discuss possible non-standard contributions to the top-quark width,
particularly the virtual effects on the standard decay
within the context of the MSSM. We also place a renewed emphasis on the
unconventional mode in the light of recent analyses of
-boson observables. It turns out that in the region of parameter space
highlighted by -boson physics, the charged Higgs mode should exhibite an
appreciable branching fraction as compared to the standard decay of the top
quark. Remarkably enough, the corresponding quantum effects in this region are
also rather large, slowly decoupling, and most likely resolvable in the next
generation of experiments at Tevatron and at LHC.Comment: One new figure added, with supplementary comments. 17 pages, LaTeX, 2
figures included via psbox. A postcript version can be obtained from
anonymous ftp at ftp://ftp.ifae.es/preprint/ft/uabft372.ps Talk presented at
the Workshop on Physics of the Top Quark, Iowa State University, May 199
- …