For a decade the fate of a one-dimensional gas of interacting bosons in an external trapping potential remained mysterious. We here show that whenever the underlying integrability of the gas is ...broken by the presence of the external potential, the inevitable diffusive rearrangements between the quasiparticles, quantified by the diffusion constants of the gas, eventually lead the system to thermalize at late times. We show that the full thermalizing dynamics can be described by the generalized hydrodynamics with diffusion and force terms, and we compare these predictions to numerical simulations. Finally, we provide an explanation for the slow thermalization rates observed in numerical and experimental settings: the hydrodynamics of integrable models is characterized by a continuity of modes, which can have arbitrarily small diffusion coefficients. As a consequence, the approach to thermalization can display prethermal plateau and relaxation dynamics with long polynomial finite-time corrections.
We consider the out-of-equilibrium dynamics of the Heisenberg anisotropic quantum spin-1/2 chain threaded by a time-dependent magnetic flux. In the spirit of the recently developed generalized ...hydrodynamics (GHD), we exploit the integrability of the model for any flux values to derive an exact description of the dynamics in the limit of slowly varying flux: the state of the system is described at any time by a time-dependent generalized Gibbs ensemble. Two dynamical regimes emerge according to the value of the anisotropy Δ. For |Δ|>1, reversibility is preserved: the initial state is always recovered whenever the flux is brought back to zero. On the contrary, for |Δ|<1, instabilities of quasiparticles produce irreversible dynamics as confirmed by the dramatic growth of entanglement entropy. In this regime, the standard GHD description becomes incomplete and we complement it via a maximum entropy production principle. We test our predictions against numerical simulations finding excellent agreement.
We solve a minimal model for an ergodic phase in a spatially extended quantum many-body system. The model consists of a chain of sites with nearest-neighbor coupling under Floquet time evolution. ...Quantum states at each site span aq-dimensional Hilbert space, and time evolution for a pair of sites is generated by aq2×q2random unitary matrix. The Floquet operator is specified by a quantum circuit of depth two, in which each site is coupled to its neighbor on one side during the first half of the evolution period and to its neighbor on the other side during the second half of the period. We show how dynamical behavior averaged over realizations of the random matrices can be evaluated using diagrammatic techniques and how this approach leads to exact expressions in the large-qlimit. We give results for the spectral form factor, relaxation of local observables, bipartite entanglement growth, and operator spreading.
Summary Background The effect of transmitted drug resistance (TDR) on first-line combination antiretroviral therapy (cART) for HIV-1 needs further study to inform choice of optimum drug regimens. We ...investigated the effect of TDR on outcome in the first year of cART within a large European collaboration. Methods HIV-infected patients of any age were included if they started cART (at least three antiretroviral drugs) for the first time after Jan 1, 1998, and were antiretroviral naive and had at least one sample for a genotypic test taken before the start of cART. We used the WHO drug resistance list and the Stanford algorithm to classify patients into three resistance categories: no TDR, at least one mutation and fully-active cART, or at least one mutation and resistant to at least one prescribed drug. Virological failure was defined as time to the first of two consecutive viral load measurements over 500 copies per mL after 6 months of therapy. Findings Of 10 056 patients from 25 cohorts, 9102 (90·5%) had HIV without TDR, 475 (4·7%) had at least one mutation but received fully-active cART, and 479 (4·8%) had at least one mutation and resistance to at least one drug. Cumulative Kaplan-Meier estimates for virological failure at 12 months were 4·2% (95% CI 3·8–4·7) for patients in the no TDR group, 4·7% (2·9–7·5) for those in the TDR and fully-active cART group, and 15·1% (11·9–19·0) for those in the TDR and resistant group (log-rank p<0·0001). The hazard ratio for the difference in virological failure between patients with TDR and resistance to at least one drug and those without TDR was 3·13 (95% CI 2·33–4·20, p<0·0001). The hazard ratio for the difference between patients with TDR receiving fully-active cART and patients without TDR was 1·47 (95% CI 0·19–2·38, p=0·12). In stratified analysis, the hazard ratio for the risk of virological failure in patients with TDR who received fully-active cART that included a non-nucleoside reverse transcriptase inhibitor (NNRTI) compared with those without TDR was 2·0 (95% CI 0·9–4·7, p=0·093). Interpretation These findings confirm present treatment guidelines for HIV, which state that the initial treatment choice should be based on resistance testing in treatment-naive patients. Funding European Community's Seventh Framework Programme FP7/2007-2013 and Gilead.
Our understanding of the background of the EPIC/pn camera on board XMM-Newton is incomplete. This affects the study of extended sources and can influence the predictions of the expected background of ...future X-ray missions, such as the Advanced Telescope for High Energy Astrophysics (ATHENA). Here we provide new results based on the analysis of the largest data set ever used. We focus on the unconcentrated component of the EPIC/pn background, supposedly related to cosmic rays interacting with detector and telescope structures. We show that the so-called out field-of-view region of the pn detector is actually exposed to the sky. After carefully cleaning from the sky contamination, the unconcentrated background measured in the out field-of-view region does not show significant spatial variations, and its time behavior is anticorrelated with the solar cycle. We find a very tight linear correlation between unconcentrated backgrounds detected in the EPIC/pn and EPIC/MOS2 cameras. This relationship permits the correct evaluation of the pn unconcentrated background of each exposure on the basis of MOS2 data, avoiding the use of the contaminated out field-of-view region of the pn, as done in standard techniques. We find a tight linear correlation between the pn unconcentrated background and the proton flux in the 630-970 MeV energy band, as measured by the EPHIN instrument on board SOHO. Through this relationship, we quantify the contribution of cosmic-ray interaction to the pn unconcentrated background. This reveals a second source that contributes to the pn unconcentrated background for a significant fraction (30%-70%). This agent does not depend on the solar cycle or vary with time and is roughly isotropic. After having ruled out several candidates, we find that the hard X-ray photons of the cosmic X-ray background satisfy all known properties of the constant component. Our findings provide an important observational confirmation of simulation results on ATHENA and suggest that a high-energy particle monitor could contribute decisively to the reproducibility of the background for both experiments on ATHENA.
We consider the nonequilibrium dynamics of a system of interacting massless fermions in a ring threaded by a magnetic flux. We focus on the quench where the flux is initially vanishing and is then ...turned on. We show that the definition of the limit of abrupt quench is problematic due to the presence of gauge invariance that has to be taken into account. We then propose a specific protocol where the dynamics is nontrivial. Employing techniques coming from the algebraic Bethe ansatz, we present an exact formula for the Loschmidt echo valid at all times as a Fredholm determinant at the free fermionic point. From the analysis of the asymptotic behavior of the Fredholm determinant, we show that the distribution of work done at small energies presents an edge singularity whose exponent can be explicitly computed. Using the correspondence between the edge singularity and the decay of the fidelity at finite size we propose a general formula for the exponent valid also in the interacting case.
A
bstract
We consider the Brownian SYK, i.e. a system of
N
Majorana (Dirac) fermions with a white-noise
q
-body interaction term. We focus on the dynamics of the Frame potentials, a measure of the ...scrambling and chaos, given by the moments of the overlap between two independent realisations of the model. By means of a Keldysh path-integral formalism, we compute its early and late-time value. We show that, for
q
> 2, the late time path integral saddle point correctly reproduces the saturation to the value of the Haar frame potential. On the contrary, for
q
= 2, the model is quadratic and consistently we observe saturation to the Haar value in the restricted space of Gaussian states (Gaussian Haar). The latter is characterised by larger system size corrections that we correctly capture by counting the Goldstone modes of the Keldysh saddle point. Finally, in the case of Dirac fermions, we highlight and resolve the role of the global U(1) symmetry.
ABSTRACT
The low luminosity, X-ray flaring activity, of the sub-class of high-mass X-ray binaries called Supergiant Fast X-ray Transients, has been investigated using XMM–Newton public observations, ...taking advantage of the products made publicly available by the EXTraS project. One of the goals of EXTraS was to extract from the XMM–Newton public archive information on the aperiodic variability of all sources observed in the soft X-ray range with EPIC (0.2–12 keV). Adopting a Bayesian block decomposition of the X-ray light curves of a sample of SFXTs, we picked out 144 X-ray flares, covering a large range of soft X-ray luminosities (1032–1036 erg s−1). We measured temporal quantities, like the rise time to and the decay time from the peak of the flares, their duration and the time interval between adjacent flares. We also estimated the peak luminosity, average accretion rate, and energy release in the flares. The observed soft X-ray properties of low-luminosity flaring activity from SFXTs is in qualitative agreement with what is expected by the application of the Rayleigh–Taylor instability model in accreting plasma near the neutron star magnetosphere. In the case of rapidly rotating neutron stars, sporadic accretion from temporary discs cannot be excluded.
Using archival as well as freshly acquired data, we assess the X-ray behavior of the Fermi/Large Area Telescope Delta *g-ray pulsars listed in the First Fermi source catalog. After revisiting the ...relationships between the pulsars' rotational energy losses and their X-ray and Delta *g-ray luminosities, we focus on the distance-independent Delta *g-to-X-ray flux ratios. When plotting our F Delta *g/F X values as a function of the pulsars' rotational energy losses, one immediately sees that pulsars with similar energetics have F Delta *g/F X spanning three decades. Such spread, most probably stemming from vastly different geometrical configurations of the X-ray and Delta *g-ray emitting regions, defies any straightforward interpretation of the plot. Indeed, while energetic pulsars do have low F Delta *g/F X values, little can be said for the bulk of the Fermi neutron stars. Dividing our pulsar sample into radio-loud and radio-quiet subsamples, we find that, on average, radio-quiet pulsars do have higher values of F Delta *g/F X , implying an intrinsic faintness of their X-ray emission and/or a different geometrical configuration. Moreover, despite the large spread mentioned above, statistical tests show a lower scatter in the radio-quiet data set with respect to the radio-loud one, pointing to a somewhat more constrained geometry for the radio-quiet objects with respect to the radio-loud ones.
During a search for X-ray transients in the XMM-Newton archive within the EXTraS project, we discovered a new X-ray source that is detected only during an ∼5 min interval of an ∼21 hr-long ...observation performed on 2011 June 21 (EXMM 023135.0-603743, probability of a random Poissonian fluctuation: ∼1.4 × 10−27). With dedicated follow-up observations, we found that its position is consistent with a star-forming galaxy (SFR = 1-2 M yr−1) at redshift z = 0.092 0.003 (d = 435 15 Mpc). At this redshift, the energy released during the transient event was 2.8 × 1046 erg in the 0.3-10 keV energy band (in the source rest frame). The luminosity of the transient, together with its spectral and timing properties, make EXMM 023135.0-603743 a gripping analog to the X-ray transient associated to SN 2008D, which was discovered during a Swift/XRT observation of the nearby (d = 27 Mpc) supernova-rich galaxy NGC 2770. We interpret the XMM-Newton event as a supernova shock break-out or an early cocoon, and show that our serendipitous discovery is broadly compatible with the rate of core-collapse supernovae derived from optical observations and much higher than that of tidal disruption events.
PDF
