37,238 research outputs found
Bouncing Eddington-inspired Born-Infeld cosmologies: an alternative to Inflation ?
We study the dynamics of a homogeneous and isotropic
Friedmann-Robertson-Walker universe in the context of the Eddington-inspired
Born-Infeld theory of gravity. We generalize earlier results, obtained in the
context of a radiation dominated universe, to account for the evolution of a
universe permeated by a perfect fluid with an arbitrary equation of state
parameter . We show that a bounce may occur for , if is
time-dependent, and we demonstrate that it is free from tensor singularities.
We argue that Eddington-inspired Born-Infeld cosmologies may be a viable
alternative to the inflationary paradigm as a solution to fundamental problems
of the standard cosmological model.Comment: 4 pages, 1 figur
Impact of FCNC top quark interactions on BR(t -> b W)
We study the effect that FCNC interactions of the top quark will have on the
branching ratio of charged decays of the top quark. We have performed an
integrated analysis using Tevatron and B-factories data and with just the
further assumption that the CKM matrix is unitary we can obtain very
restrictive bounds on the strong and electroweak FCNC branching ratios Br(t ->
q X) < 4.0 10^{-4}, where X is any vector boson and a sum in q = u,c is
implied.Comment: 10 pages, 5 figure
Contributions from dimension six strong flavor changing operators to top anti-top, top plus gauge boson, and top plus Higgs boson production at the LHC
We study the effects of a set of dimension six flavor changing effective
operators on several processes of production of top quarks at the LHC. Namely,
top anti-top production and associated production of a top and a gauge or Higgs
boson. Analytical expressions for the cross sections of these processes are
derived and presented.Comment: 14 pages, 10 figures, refs. adde
Tensor Microwave Anisotropies from a Stochastic Magnetic Field
We derive an expression for the angular power spectrum of cosmic microwave
background anisotropies due to gravity waves generated by a stochastic magnetic
field and compare the result with current observations; we take into account
the non-linear nature of the stress energy tensor of the magnetic field.
For almost scale invariant spectra, the amplitude of the magnetic field at
galactic scales is constrained to be of order 10^{-9} Gauss. If we assume that
the magnetic field is damped below the Alfven damping scale, we find that its
amplitude at
0.1 h^{-1}Mpc, B_\lambda, is constrained to be B_\lambda<7.9 x10^{-6} e^{3n}
Gauss, for n-3/2, where
n is the spectral index of the magnetic field and H_0=100h km s^{-1}Mpc^{-1} is
the Hubble constant today.Comment: 6 pages, 1 figure, accepted for publication in Phys. Rev.
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