1,519 research outputs found
Chaos in Kundt type III Spacetimes
We consider geodesics motion in a particular Kundt type III spacetime in
which Einstein-Yang-Mills equations admit solutions. On a particular surface as
constraint we project the geodesics into the (x,y) plane and treat the problem
as a 2-dimensional one. Our numerical study shows that chaotic behavior emerges
under reasonable conditions.Comment: 4 Figure
Nematicity as a route to a magnetic field-induced spin density wave order; application to the high temperature cuprates
The electronic nematic order characterized by broken rotational symmetry has
been suggested to play an important role in the phase diagram of the high
temperature cuprates. We study the interplay between the electronic nematic
order and a spin density wave order in the presence of a magnetic field. We
show that a cooperation of the nematicity and the magnetic field induces a
finite coupling between the spin density wave and spin-triplet staggered flux
orders. As a consequence of such a coupling, the magnon gap decreases as the
magnetic field increases, and it eventually condenses beyond a critical
magnetic field leading to a field-induced spin density wave order. Both
commensurate and incommensurate orders are studied, and the experimental
implications of our findings are discussed.Comment: 5 pages, 3 figure
Equation of state and Beginning of Thermalization After Preheating
We study the out-of-equilibrium nonlinear dynamics of fields after
post-inflationary preheating. During preheating, the energy in the homogeneous
inflaton is exponentially rapidly transfered into highly occupied
out-of-equilibrium inhomogeneous modes, which subsequently evolve towards
equilibrium. The infrared modes excited during preheating evolve towards a
saturated distribution long before thermalization completes. We compute the
equation of state during and immediately after preheating. It rapidly evolves
towards radiation domination long before the actual thermal equilibrium is
established. The exact time of this transition is a non-monotonic function of
the coupling between the inflaton and the decay products, and it varies only
very weakly (around 10^(-35) s) as this coupling changes over several orders of
magnitude. This result is applied to refine the relation between the number of
efoldings N and the physical wavelength of perturbations generated during
inflation. We also discuss the implications for the theory of modulated
perturbations from preheating. We finally argue that many questions of the
thermal history of the universe should be addressed in terms of
pre-thermalization, illustrating this point with a calculation of perturbative
production of gravitinos immediately after chaotic inflation. We also highlight
the effects of three-legs inflaton interactions on the dynamics of preheating
and thermalization in an expanding universe.Comment: 15 pages, 13 figure
Suppression of left-handed properties in disordered metamaterials
We study the effect of disorder on the effective magnetic response of
composite left-handed metamaterials and their specific properties such as
negative refraction. We show that relatively weak disorder in the split-ring
resonators can reduce and even completely eliminate the frequency domain where
the composite material demonstrates the left-handed properties. We introduce
the concept of the order parameter to describe novel physics of this effect.Comment: 4 pages, 2 figure
Lorentzian manifolds and scalar curvature invariants
We discuss (arbitrary-dimensional) Lorentzian manifolds and the scalar
polynomial curvature invariants constructed from the Riemann tensor and its
covariant derivatives. Recently, we have shown that in four dimensions a
Lorentzian spacetime metric is either -non-degenerate, and hence
locally characterized by its scalar polynomial curvature invariants, or is a
degenerate Kundt spacetime. We present a number of results that generalize
these results to higher dimensions and discuss their consequences and potential
physical applications.Comment: submitted to CQ
Superconducting quantum phase transitions tuned by magnetic impurity and magnetic field in ultrathin a-Pb films
Superconducting quantum phase transitions tuned by disorder (d), paramagnetic
impurity (MI) and perpendicular magnetic field (B) have been studied in
homogeneously disordered ultrathin a-Pb films. The MI-tuned transition is
characterized by progressive suppression of the critical temperature to zero
and a continuous transition to a weakly insulating normal state with increasing
MI density. In all important aspects, the d-tuned transition closely resembles
the MI-tuned transition and both appear to be fermionic in nature. The B-tuned
transition is qualitatively different and probably bosonic. In the critical
region it exhibits transport behavior that suggests a B-induced mesoscale phase
separation and presence of Cooper pairing in the insulating state.Comment: 17 pages, 4 figure
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