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Ciudad Universitaria, Argentina

Freitas N.,FCEyN | Paz J.P.,CONICET
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics

We present an analytic expression for the heat current through a general harmonic network coupled with Ohmic reservoirs. We use a method that enables us to express the stationary state of the network in terms of the eigenvectors and eigenvalues of a generalized cubic eigenvalue problem. In this way, we obtain exact formulas for the heat current and the local temperature inside the network. Our method does not rely on the usual assumptions of weak coupling to the environments or on the existence of an infinite cutoff in the environmental spectral densities. We use this method to study nonequilibrium processes without the weak coupling and Markovian approximations. As a first application of our method, we revisit the problem of heat conduction in two- and three-dimensional crystals with binary mass disorder. We complement previous results showing that for small systems the scaling of the heat current with the system size greatly depends on the strength of the interaction between system and reservoirs. This somewhat counterintuitive result seems not to have been noticed before. © 2014 American Physical Society. Source

Freitas J.N.,FCEyN | Paz J.P.,FCEyN | Paz J.P.,Institute Fisica Of Buenos Aires
Physical Review A - Atomic, Molecular, and Optical Physics

We analyze the evolution of the Gaussian discord between two resonant harmonic oscillators coupled to a common environment. For this, we use the same tools we applied before to fully characterize the evolution of the entanglement in this system. The asymptotic value of Gaussian discord is obtained as a function of parameters characterizing the environment (temperature, couplings, etc.) and the initial state of the system (initial squeezing, initial purity, etc.) The type of Gaussian measurement optimizing the extraction of information between the oscillators is fully characterized by means of a phase diagram. Such a diagram (with phases corresponding to homodyne or heterodyne measurements) has similar topology to the one describing dynamical phases for the entanglement. We present evidence pointing to the fact that Gaussian discord is not always a good approximation of true discord as the asymptotic value of the former is shown to be a nondecreasing function of temperature (in the high-temperature regime), reaching an asymptotic value of ln(2) for a pure initial state (and lower values for mixed initial states). © 2012 American Physical Society. Source

Alvarez E.,National University of San Luis | Leskow E.C.,FCEyN | Zurita J.,University of Zurich
Physical Review D - Particles, Fields, Gravitation and Cosmology

We study the constraints on the Lee-Wick Higgs sector arising from direct collider searches. We work in an effective-field theory framework, where all of the Lee-Wick partners are integrated out, with the sole exception of the Lee-Wick Higgs bosons. The resulting theory is a two-Higgs doublet model where the second doublet has wrong-sign kinetic and mass terms. We include the bounds coming from direct Higgs searches at both LEP and Tevatron using the code HiggsBounds, and show the currently excluded parameter space. We also analyze the prospects of LHC Run-I, finding that with a total integrated luminosity of 5fb-1 and a center-of-mass energy of 7 TeV, most of the parameter space for the standard model-like CP-even Higgs will be probed. © 2011 American Physical Society. Source

Peralta-Ramos J.,FCEyN | Calzetta E.,FCEyN
Physical Review C - Nuclear Physics

We apply divergence-type theory (DTT) dissipative hydrodynamics to study the 2+1 space-time evolution of the fireball created in Au+Au relativistic heavy-ion collisions at √sNN=200 GeV. DTTs are exact hydrodynamic theories that do not rely on velocity gradient expansions and therefore go beyond second-order theories. We numerically solve the equations of motion of the DTT for Glauber initial conditions and compare the results with those of second-order theory based on conformal invariance (Baier-Romatschke- Son-Starinets model) and with data. We find that the charged-hadron minimum-bias elliptic flow reaches its maximum value at lower pT in the DTT, and that the DTT allows for a value of η/s slightly larger than that of the BRSS. Our results show that the differences between viscous hydrodynamic formalisms are a significant source of uncertainty in the precise extraction of η/s from experiments. © 2010 The American Physical Society. Source

Wisniacki D.A.,FCEyN | Roncaglia A.J.,FCEyN
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics

The local density of states or its Fourier transform, usually called fidelity amplitude, are important measures of quantum irreversibility due to imperfect evolution. In this Rapid Communication we study both quantities in a paradigmatic many body system, the Dicke Hamiltonian, where a single-mode bosonic field interacts with an ensemble of N two-level atoms. This model exhibits a quantum phase transition in the thermodynamic limit, while for finite instances the system undergoes a transition from quasi-integrability to quantum chaotic. We show that the width of the local density of states clearly points out the imprints of the transition from integrability to chaos but no trace remains of the quantum phase transition. The connection with the decay of the fidelity amplitude is also established. © 2013 American Physical Society. Source

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