197,559 research outputs found
Teresita Román de Zurek e hijos
No full textTeresita Román de Zurek e hijos Catalina, Teresa, Margarita su esposo Sergio Londoño y cuñado Enrique. Doctor Guillermo Rueda M. Presidente Cruz Roja Nacional
Monojet versus the rest of the world I: t-channel models
No full textMonojet searches using Effective Field Theory (EFT) operators are usually interpreted as a robust and model independent constraint on direct detection (DD) scattering cross-sections. At the same time, a mediator particle must be present to produce the dark matter (DM) at the LHC. This mediator particle may be produced on shell, so that direct searches for the mediating particle can constrain the effective operator being applied to monojet constraints. In this first paper, we do a case study on t-channel models in monojet searches, where the (Standard Model singlet) DM is pair produced via a t-channel mediating particle, whose supersymmetric analogue is the squark. We compare monojet constraints to direct constraints on single or pair production of the mediator from multi-jets plus missing energy searches and we identify the regions where the latter dominate over the former. We show that computing bounds using supersymmetric simplified models and in the narrow width approximation, as done in previous work in the literature, misses important quantitative effects. We perform a full event simulation and statistical analysis, and we compute the effects of both on- and off-shell production of the mediating particle, showing that for both the monojet and multi-jets plus missing energy searches, previously derived bounds provided more conservative bounds than what can be extracted by including all relevant processes in the simulation. Monojets and searches for super-symmetry (SUSY) provide comparable bounds on a wide range of the parameter space, with SUSY searches usually providing stronger bounds, except in the regions where the DM particle and the mediator are very mass degenerate. The EFT approximation rarely is able to reproduce the actual limits. In a second paper to follow, we consider the case of s-channel mediators
Complex Dark Sectors and Large Bound States of Dark Matter
No full textWe discuss models of hidden sector dark matter, and a recent generic proposal for large bound states of asymmetric dark matter
When Casimir meets Kibble-Zurek
No full textVerification of the dynamical Casimir effect (DCE) in optical systems is still elusive due to the very demanding requirements for its experimental implementation. This typically requires very fast changes in the boundary conditions of the problem. We show that an ensemble of two-level atoms collectively coupled to the electromagnetic field of a cavity, driven at low frequencies and close to a quantum phase transition, stimulates the production of photons from the vacuum. This paves the way for an effective simulation of the DCE through a mechanism that has recently found experimental demonstration. The spectral properties of the emitted radiation reflect the critical nature of the system and allow us to link the detection of DCE to the Kibble-Zurek mechanism for the production of defects when crossing a continuous phase transition.</p
Wootters-Zurek quantum-copying machine: The higher-dimensional case
No full textWe examine Wootters-Zurek quantum-copying machine on a higher-dimensional state space and evaluate the index Da of copying quality and three indexes Dab(1), Dab(2) and Dab(3) of entanglement of the output modes. © 2002 Elsevier Science B.V. All rights reserved
Mono-X versus direct searches: simplified models for dark matter at the LHC
No full textWe consider simplified models for dark matter (DM) at the LHC, focused on mono-Higgs, -Z or -b produced in the final state. Our primary purpose is to study the LHC reach of a relatively complete set of simplified models for these final states, while comparing the reach of the mono-X DM search against direct searches for the mediating particle. We find that direct searches for the mediating particle, whether in di-jets, jets+[InlineMediaObject not available: see fulltext.], multi-b+[InlineMediaObject not available: see fulltext.], or di-boson+[InlineMediaObject not available: see fulltext.], are usually stronger. We draw attention to the cases that the mono-X search is strongest, which include regions of parameter space in inelastic DM, two Higgs doublet, and squark mediated production models with a compressed spectrum
Illuminating Dark Matter : Proceedings of a Simons Symposium
No full textBased on a Simons Symposium held in 2018, the proceedings in this volume focus on the theoretical, numerical, and observational quest for dark matter in the universe. Present ground-based and satellite searches have so far severely constrained the long-proposed theoretical models for dark matter. Nevertheless, there is continuously growing astrophysical and cosmological evidence for its existence. To address present and future developments in the field, novel ideas, theories, and approaches are called for. The symposium gathered together a new generation of experts pursuing innovative, more complex theories of dark matter than previously considered.This is being done hand in hand with experts in numerical astrophysical simulations and observational techniques—all paramount for deciphering the nature of dark matter. The proceedings volume provides coverage of the most advanced stage of understanding dark matter in various new frameworks. The collection will be useful for graduate students, postdocs, and investigators interested in cutting-edge research on one of the biggest mysteries of our universe
The 'Grenoble' cosmological experiment - The Kibble-Zurek scenario in superfluid He-3.
No full textWe describe in this lecture neutron irradiation experiments performed on superluid He-3-B at ultralow temperatures. The measurement of the thermal energy released by the neutron-He-3 nuclear reaction reveals the existence of an energy deficit. We propose that this deficit can be ascribed to the formation energy of vortices, these topological defects being created by the Kibble-Zurek mechanism as the region heated to the normal state by the neutron irradiation recrosses the superfluid transition. A quantitative agreement is found with Zurek's predictions for the density of topological defects created during a rapid quench through a symmetry-breaking phase transition
Defect Formation beyond Kibble-Zurek Mechanism and Holography
No full textWe study the dynamic after a smooth quench across a continuous transition from the disordered phase to the ordered phase. Based on scaling ideas, linear response, and the spectrum of unstable modes, we develop a theoretical framework, valid for any second-order phase transition, for the early-time evolution of the condensate in the broken phase. Our analysis unveils a novel period of nonadiabatic evolution after the system passes through the phase transition, where a parametrically large amount of coarsening occurs before a well-defined condensate forms. Our formalism predicts a rate of defect formation parametrically smaller than the Kibble-Zurek prediction and yields a criterion for the breakdown of Kibble-Zurek scaling for sufficiently fast quenches. We numerically test our formalism for a thermal quench in a (2+1)-dimensional holographic superfluid. These findings, of direct relevance in a broad range of fields including cold atom, condensed matter, statistical mechanics, and cosmology, are an important step toward a more quantitative understanding of dynamical phase transitions
Influence of exertional oscillatory ventilation on exercise performance in heart failure
No full textBACKGROUND: Exertional oscillatory ventilation (EOV) in heart failure may potentiate the negative effects of low cardiac output and high ventilation on exercise performance. We hypothesized that the presence of EOV might, per se, influence exercise capacity as evaluated by maximal cardiopulmonary exercise test. METHODS AND RESULTS: We identified 78 severe chronic heart failure patient pairs with and without EOV. Patients were matched for sex, age and peak oxygen consumption (VO2). Patients with EOV showed, for the same peak VO2, a lower workload (WL) at peak (DeltaWatts=5.8+/-23.0, P=0.027), a less efficient ventilation (higher VE/VCO2 slope: 38.0+/-8.3 vs. 32.8+/-6.3, P<0.001), lower peak exercise tidal volume (1.49+/-0.36 L vs. 1.61+/-0.46 L, P=0.015) and higher peak respiratory rate (34+/-7/min vs. 31+/-6/min, P=0.002). In 33 patients, EOV disappeared during exercise, whereas in 45 patients EOV persisted. Fifty percent of EOV disappearing patients had an increase in the VO2/WL relationship after EOV regression, consistent with a more efficient oxygen delivery to muscles. No cardiopulmonary exercise test parameter was associated with the different behaviour of VO2/WL. CONCLUSION: The presence of EOV negatively influences exercise performance of chronic heart failure patients likely because of an increased cost of breathing. EOV disappearance during exercise is associated with a more efficient oxygen delivery in several cases
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