Quasiparticle entanglement: redefinition of the vacuum and reduced density matrix approach

A scattering approach to entanglement in mesoscopic conductors with independent fermionic quasiparticles is discussed. We focus on conductors in the tunneling limit, where a redefinition of the quasiparticle vacuum transforms the wavefunction from a manybody product state of noninteracting particles to a state describing entangled two-particle excitations out of the new vacuum. The approach is illustrated with two examples (i) a normal-superconducting system, where the transformation is made between Bogoliubov-de Gennes quasiparticles and Cooper pairs, and (ii) a normal system, where the transformation is made between electron quasiparticles and electron-hole pairs. This is compared to a scheme where an effective two-particle state is derived from the manybody scattering state by a reduced density matrix approach.Comment: Submitted to New Journal of Physics, Focused Issue on "Solid State Quantum Information". 19 pages, 7 figure

Elliptic flow of charged particles in Pb-Pb collisions at 2.76 TeV

We report the first measurement of charged particle elliptic flow in Pb-Pb collisions at 2.76 TeV with the ALICE detector at the CERN Large Hadron Collider. The measurement is performed in the central pseudorapidity region (|$\eta$|<0.8) and transverse momentum range 0.2< $p_{\rm T}$< 5.0 GeV/$c$. The elliptic flow signal v$_2$, measured using the 4-particle correlation method, averaged over transverse momentum and pseudorapidity is 0.087 $\pm$ 0.002 (stat) $\pm$ 0.004 (syst) in the 40-50% centrality class. The differential elliptic flow v$_2(p_{\rm T})$ reaches a maximum of 0.2 near $p_{\rm T}$ = 3 GeV/$c$. Compared to RHIC Au-Au collisions at 200 GeV, the elliptic flow increases by about 30%. Some hydrodynamic model predictions which include viscous corrections are in agreement with the observed increase.Comment: 10 pages, 4 captioned figures, published version, figures at http://aliceinfo.cern.ch/ArtSubmission/node/389

Blazar spectral variability as explained by a twisted inhomogeneous jet

Blazars are active galactic nuclei, which are powerful sources of radiation whose central engine is located in the core of the host galaxy. Blazar emission is dominated by non-thermal radiation from a jet that moves relativistically towards us, and therefore undergoes Doppler beaming1. This beaming causes flux enhancement and contraction of the variability timescales, so that most blazars appear as luminous sources characterized by noticeable and fast changes in brightness at all frequencies. The mechanism that produces this unpredictable variability is under debate, but proposed mechanisms include injection, acceleration and cooling of particles2, with possible intervention of shock waves3,4 or turbulence5. Changes in the viewing angle of the observed emitting knots or jet regions have also been suggested as an explanation of flaring events6,7,8,9,10 and can also explain specific properties of blazar emission, such as intra-day variability11, quasi-periodicity12,13 and the delay of radio flux variations relative to optical changes14. Such a geometric interpretation, however, is not universally accepted because alternative explanations based on changes in physical conditions—such as the size and speed of the emitting zone, the magnetic field, the number of emitting particles and their energy distribution—can explain snapshots of the spectral behaviour of blazars in many cases15,16. Here we report the results of optical-to-radio-wavelength monitoring of the blazar CTA 102 and show that the observed long-term trends of the flux and spectral variability are best explained by an inhomogeneous, curved jet that undergoes changes in orientation over time. We propose that magnetohydrodynamic instabilities17 or rotation of the twisted jet6 cause different jet regions to change their orientation and hence their relative Doppler factors. In particular, the extreme optical outburst of 2016–2017 (brightness increase of six magnitudes) occurred when the corresponding emitting region had a small viewing angle. The agreement between observations and theoretical predictions can be seen as further validation of the relativistic beaming theory

Investigating the multiwavelength behaviour of the flat spectrum radio quasar CTA 102 during 2013-2017

We present a multiwavelength study of the flat-spectrum radio quasar CTA 102 during 2013-2017. We use radio-to-optical data obtained by the Whole Earth Blazar Telescope, 15 GHz data from the Owens Valley Radio Observatory, 91 and 103 GHz data from the Atacama Large Millimeter Array, near-infrared data from the Rapid Eye Monitor telescope, as well as data from the Swift (optical-UV and X-rays) and Fermi (gamma-rays) satellites to study flux and spectral variability and the correlation between flux changes at different wavelengths. Unprecedented gamma-ray flaring activity was observed during 2016 November-2017 February, with four major outbursts. A peak flux of (2158 +/- 63) x 10(-8) ph cm(-2) s(-1), corresponding to a luminosity of (2.2 +/- 0.1) x10(50) erg s(-1), was reached on 2016 December 28. These four gamma-ray outbursts have corresponding events in the near-infrared, optical, and UV bands, with the peaks observed at the same time. A general agreement between X-ray and gamma-ray activity is found. The gamma-ray flux variations show a general, strong correlation with the optical ones with no time lag between the two bands and a comparable variability amplitude. This gamma-ray/optical relationship is in agreement with the geometrical model that has successfully explained the low-energy flux and spectral behaviour, suggesting that the long-term flux variations are mainly due to changes in the Doppler factor produced by variations of the viewing angle of the emitting regions. The difference in behaviour between radio and higher energy emission would be ascribed to different viewing angles of the jet regions producing their emission

Transverse momentum spectra of charged particles in proton-proton collisions at s=900\sqrt{s} = 900 GeV with ALICE at the LHC

The inclusive charged particle transverse momentum distribution is measured in proton-proton collisions at $\sqrt{s} = 900$ GeV at the LHC using the ALICE detector. The measurement is performed in the central pseudorapidity region $(|\eta|<0.8)$ over the transverse momentum range $0.15<p_{\rm T}<10$ GeV/$c$. The correlation between transverse momentum and particle multiplicity is also studied. Results are presented for inelastic (INEL) and non-single-diffractive (NSD) events. The average transverse momentum for $|\eta|<0.8$ is $\left<p_{\rm T}\right>_{\rm INEL}=0.483\pm0.001$ (stat.) $\pm0.007$ (syst.) GeV/$c$ and \left_{\rm NSD}=0.489\pm0.001 (stat.) $\pm0.007$ (syst.) GeV/$c$, respectively. The data exhibit a slightly larger $\left<p_{\rm T}\right>$ than measurements in wider pseudorapidity intervals. The results are compared to simulations with the Monte Carlo event generators PYTHIA and PHOJET.Comment: 20 pages, 8 figures, 2 tables, published version, figures at http://aliceinfo.cern.ch/ArtSubmission/node/390

Investigating the multiwavelength behaviour of the flat spectrum radio quasar CTA 102 during 2013–2017

We present a multiwavelength study of the flat-spectrum radio quasar CTA 102 during 2013-2017. We use radio-to-optical data obtained by the Whole Earth Blazar Telescope, 15 GHz data from the Owens Valley Radio Observatory, 91 and 103 GHz data from the Atacama Large Millimeter Array, near-infrared data from the Rapid Eye Monitor telescope, as well as data from the Swift (optical-UV and X-rays) and Fermi (gamma-rays) satellites to study flux and spectral variability and the correlation between flux changes at different wavelengths. Unprecedented gamma-ray flaring activity was observed during 2016 November-2017 February, with four major outbursts. A peak flux of (2158 +/- 63) x 10(-8) ph cm(-2) s(-1), corresponding to a luminosity of (2.2 +/- 0.1) x10(50) erg s(-1), was reached on 2016 December 28. These four gamma-ray outbursts have corresponding events in the near-infrared, optical, and UV bands, with the peaks observed at the same time. A general agreement between X-ray and gamma-ray activity is found. The gamma-ray flux variations show a general, strong correlation with the optical ones with no time lag between the two bands and a comparable variability amplitude. This gamma-ray/optical relationship is in agreement with the geometrical model that has successfully explained the low-energy flux and spectral behaviour, suggesting that the long-term flux variations are mainly due to changes in the Doppler factor produced by variations of the viewing angle of the emitting regions. The difference in behaviour between radio and higher energy emission would be ascribed to different viewing angles of the jet regions producing their emission.Bulgarian National Science Fund of the Ministry of Education and Science [DN 08-1/2016, DN 18-13/2017, KP-06-H28/3 (2018)]; Foundation for Research and Technology -Hellas; Max-Planck-Institut fur Extraterrestrische Physik; Shota Rustaveli National Science Foundation [FR/217554/16]; Russian Science FoundationRussian Science Foundation (RSF) [17-12-01029]; Institute of Astronomy and Rozhen National Astronomical Observatory [176011, 176004, 176021]; Ministry of Education, Science and Technological Development of the Republic of Serbia; DGAPA (Universidad Nacional Autonoma de M'exico)Universidad Nacional Autonoma de Mexico; PAPIIT projectPrograma de Apoyo a Proyectos de Investigacion e Innovacion Tecnologica (PAPIIT) [IN114917]; Smithsonian InstitutionSmithsonian Institution; Academia SinicaAcademia Sinica - Taiwan; NASA/Fermi Guest Investigator [NNX12AO93G, NNX15AU81G]; Bulgarian National Science Programme 'Young Scientists and Postdoctoral Students 2019', Bulgarian National Science Fund [DN18-10/2017]; National RI Roadmap Projects [DO1-157/28.08.2018, DO1-153/28.08.2018]; Ministry of Education and Science of the Republic of Bulgaria; Regional Government of the Aosta Valley - 'Research and Education' grants from Fondazione CRT; CONICYT project Basal [AFB-170002]; Russian Government Program of Competitive Growth of Kazan Federal University; National Aeronautics and Space AdministrationNational Aeronautics & Space Administration (NASA); Department of Energy in the United StatesUnited States Department of Energy (DOE); Commissariat a l'Energie Atomique and the Centre National de la Recherche Scientifique/Institut National de Physique Nucleaire et de Physique des Particules in FranceCentre National de la Recherche Scientifique (CNRS); Agenzia Spaziale ItalianaItalian Space Agency; Istituto Nazionale di Fisica Nucleare in ItalyIstituto Nazionale di Fisica Nucleare; Ministry of Education, Culture, Sports, Science and Technology (MEXT)Ministry of Education, Culture, Sports, Science and Technology, Japan (MEXT); K. A. Wallenberg FoundationKnut & Alice Wallenberg Foundation; Swedish Research CouncilSwedish Research Council; Swedish National Space Board in Sweden; Istituto Nazionale di Astrofisica in ItalyIstituto Nazionale Astrofisica; Centre National d'Etudes Spatiales in FranceCentre National D'etudes Spatiales; United States Department of Energy (DOE) [DE-AC02-76SF00515]; National Aeronautics & Space Administration (NASA) [NNX08AW31G, NNX11A043G, NNX14AQ89G]; National Science Foundation (NSF) [AST-0808050, AST-1109911]; NASA's Goddard Space Flight CenterThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Centrality Dependence of the Charged-Particle Multiplicity Density at Midrapidity in Pb-Pb Collisions at root s(NN)=2.76 TeV

The centrality dependence of the charged-particle multiplicity density at midrapidity in Pb-Pb collisions at root s(NN) = 2: 76 TeV is presented. The charged-particle density normalized per participating nucleon pair increases by about a factor of 2 from peripheral (70%-80%) to central (0%-5%) collisions. The centrality dependence is found to be similar to that observed at lower collision energies. The data are compared with models based on different mechanisms for particle production in nuclear collisions

Charged-Particle Multiplicity Density at Midrapidity in Central Pb-Pb Collisions at root s(NN)=2.76 TeV

The first measurement of the charged-particle multiplicity density at midrapidity in Pb-Pb collisions at a center-of-mass energy per nucleon pair root s(NN) = 2.76 TeV is presented. For an event sample corresponding to the most central 5% of the hadronic cross section, the pseudorapidity density of primary charged particles at midrapidity is 1584 +/- 4(stat) +/- 76(syst), which corresponds to 8.3 +/- 0.4(syst) per participating nucleon pair. This represents an increase of about a factor 1.9 relative to pp collisions at similar collision energies, and about a factor 2.2 to central Au-Au collisions at root s(NN) = 0.2 TeV. This measurement provides the first experimental constraint for models of nucleus-nucleus collisions at LHC energies