11,464 research outputs found
Observable non-gaussianity from gauge field production in slow roll inflation, and a challenging connection with magnetogenesis
In any realistic particle physics model of inflation, the inflaton can be
expected to couple to other fields. We consider a model with a dilaton-like
coupling between a U(1) gauge field and a scalar inflaton. We show that this
coupling can result in observable non-gaussianity, even in the conventional
regime where inflation is supported by a single scalar slowly rolling on a
smooth potential: the time dependent inflaton condensate leads to amplification
of the large-scale gauge field fluctuations, which can feed-back into the
scalar/tensor cosmological perturbations. In the squeezed limit, the resulting
bispectrum is close to the local one, but it shows a sizable and characteristic
quadrupolar dependence on the angle between the shorter and the larger modes in
the correlation. Observable non-gaussianity is obtained in a regime where
perturbation theory is under control. If the gauge field is identified with the
electromagnetic field, the model that we study is a realization of the
magnetogenesis idea originally proposed by Ratra, and widely studied. This
identification (which is not necessary for the non-gaussianity production) is
however problematic in light of a strong coupling problem already noted in the
literature.Comment: 28 pages, no figures. Final versio
Breakdown of correspondence in chaotic systems: Ehrenfest versus localization times
Breakdown of quantum-classical correspondence is studied on an experimentally
realizable example of one-dimensional periodically driven system. Two relevant
time scales are identified in this system: the short Ehrenfest time t_h and the
typically much longer localization time scale T_L. It is shown that
surprisingly weak modification of the Hamiltonian may eliminate the more
dramatic symptoms of localization without effecting the more subtle but
ubiquitous and rapid loss of correspondence at t_h.Comment: 4 pages, 5 figures, replaced with a version submitted to PR
Topological Kondo effect with Majorana fermions
The Kondo effect is a striking consequence of the coupling of itinerant
electrons to a quantum spin with degenerate energy levels. While degeneracies
are commonly thought to arise from symmetries or fine-tuning of parameters, the
recent emergence of Majorana fermions has brought to the fore an entirely
different possibility: a "topological degeneracy" which arises from the
nonlocal character of Majorana fermions. Here we show that nonlocal quantum
spins formed from these degrees of freedom give rise to a novel "topological
Kondo effect". This leads to a robust non-Fermi liquid behavior, known to be
difficult to achieve in the conventional Kondo context. Focusing on mesoscopic
superconductor devices, we predict several unique transport signatures of this
Kondo effect, which would demonstrate the non-local quantum dynamics of
Majorana fermions, and validate their potential for topological quantum
computation
Deeply inelastic scattering off nuclei at RHIC
We discuss the physics case for an electron--nucleus collider at RHIC.Comment: 36 pages LaTex, 10 figures, Plenary talk at EPIC meeting, MIT,
September 14th-16th, 200
Large Dimensions and String Physics in Future Colliders
We review the status of low-scale string theories and large extra-dimensions.
After an overview on different string realizations, we discuss some of the main
important problems and we summarize present bounds on the size of possible
extra-dimensions from collider experiments.Comment: 58 pages, latex, 8 eps figure
Precision Unification and Proton Decay in F-Theory GUTs with High Scale Supersymmetry
F-theory GUTs provide a promising UV completion for models with approximate
gauge coupling unification, such as the (non-supersymmetric) Standard Model.
More specifically, if the superparters have masses well above the TeV scale,
the resulting imperfection in unification can be accounted for by the, in
principle calculable, classical F-theory correction at the high scale. In this
paper we argue for the correct form of the F-theory corrections to unification,
including KK mode loop effects. However, the price of compensating the
imprecise unification in such High Scale SUSY models with F-theory corrections
is that the GUT scale is lowered, potentially leading to a dangerously high
proton decay rate from dimension-6 operators. We analyse the possibility of
suppressing the decay rate by the localization of gauge bosons in higher
dimensions. While this effect can be very strong for the zero modes, we find
that in the simplest models of this type it is difficult to realize a
significant suppression for higher modes (Landau levels). Notably, in the
absence of substantial suppressions to the proton decay rate, the superpartners
must be lighter than 100 TeV to satisfy proton decay constraints. We highlight
that multiple correlated signals of proton decay could verify this scenario.Comment: 44 pages. v2: References adde
Squeezing of Atoms in a Pulsed Optical Lattice
We study the process of squeezing of an ensemble of cold atoms in a pulsed
optical lattice. The problem is treated both classically and
quantum-mechanically under various thermal conditions. We show that a dramatic
compression of the atomic density near the minima of the optical potential can
be achieved with a proper pulsing of the lattice. Several strategies leading to
the enhanced atomic squeezing are suggested, compared and optimized.Comment: Latex, 9 pages, 10 figures, submitted to PR
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