16,032 research outputs found
Inflationary dynamics of kinetically-coupled gauge fields
We investigate the inflationary dynamics of two kinetically-coupled massless
gauge fields with time-varying kinetic-term coefficients. Ensuring that
the system does not have strongly coupled regimes shrinks the parameter space.
Also, we further restrict ourselves to systems that can be quantized using the
standard creation, annihilation operator algebra. This second constraint limits
us to scenarios where the system can be diagonalized into the sum of two
decoupled, massless, vector fields with a varying kinetic-term coefficient.
Such a system might be interesting for magnetogenesis because of how the
strong coupling problem generalizes. We explore this idea by assuming that one
of the gauge fields is the Standard Model field and that the other dark
gauge field has no particles charged under its gauge group. We consider whether
it would be possible to transfer a magnetic field from the dark sector,
generated perhaps before the coupling was turned on, to the visible sector. We
also investigate whether the simple existence of the mixing provides more
opportunities to generate magnetic fields. We find that neither possibility
works efficiently, consistent with the well-known difficulties in inflationary
magnetogenesis.Comment: 17 pages, 0 figures. Matches JCAP versio
How to project onto extended second order cones
The extended second order cones were introduced by S. Z. N\'emeth and G.
Zhang in [S. Z. N\'emeth and G. Zhang. Extended Lorentz cones and variational
inequalities on cylinders. J. Optim. Theory Appl., 168(3):756-768, 2016] for
solving mixed complementarity problems and variational inequalities on
cylinders. R. Sznajder in [R. Sznajder. The Lyapunov rank of extended second
order cones. Journal of Global Optimization, 66(3):585-593, 2016] determined
the automorphism groups and the Lyapunov or bilinearity ranks of these cones.
S. Z. N\'emeth and G. Zhang in [S.Z. N\'emeth and G. Zhang. Positive operators
of Extended Lorentz cones. arXiv:1608.07455v2, 2016] found both necessary
conditions and sufficient conditions for a linear operator to be a positive
operator of an extended second order cone. This note will give formulas for
projecting onto the extended second order cones. In the most general case the
formula will depend on a piecewise linear equation for one real variable which
will be solved by using numerical methods
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
On the spherical convexity of quadratic functions
In this paper we study the spherical convexity of quadratic functions on
spherically convex sets. In particular, conditions characterizing the spherical
convexity of quadratic functions on spherical convex sets associated to the
positive orthants and Lorentz cones are given
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