arXiv subjects

Andrea De Luca

Publications and source records attributed to Andrea De Luca.

At least 91 records · Page 5Linked to original sources

arXiv2017

Non Relativistic Limit of Integrable QFT and Lieb-Liniger Models

In this paper we study a suitable limit of integrable QFT with the aim to identify continuous non-relativistic integrable models with local interactions. This limit amounts to sending to infinity the speed of light c but simultaneously adjusting the coupling constant g of the quantum field theories in such a way to keep finite the energies of the various excitations. The QFT considered here are Toda Field Theories and the O(N) non-linear sigma model. In both cases the resulting non-relativistic integrable models consist only of Lieb-Liniger models, which are fully decoupled for the Toda theories while symmetrically coupled for the O(N) model. These examples provide explicit evidence of the universality and ubiquity of the Lieb-Liniger models and, at the same time, suggest that these models may exhaust the list of possible non-relativistic integrable theories of bosonic particles with local interactions.

cond-mat.stat-mech↗

arXiv2016

Magnetar-like activity from the central compact object in the SNR RCW103

The 6.67 hr periodicity and the variable X-ray flux of the central compact object (CCO) at the center of the SNR RCW 103, named 1E 161348-5055, have been always difficult to interpret within the standard scenarios of an isolated neutron star or a binary system. On 2016 June 22, the Burst Alert Telescope (BAT) onboard Swift detected a magnetar-like short X-ray burst from the direction of 1E 161348-5055, also coincident with a large long-term X-ray outburst. Here we report on Chandra, NuSTAR, and Swift (BAT and XRT) observations of this peculiar source during its 2016 outburst peak. In particular, we study the properties of this magnetar-like burst, we discover a hard X-ray tail in the CCO spectrum during outburst, and we study its long-term outburst history (from 1999 to July 2016). We find the emission properties of 1E 161348-5055 consistent with it being a magnetar. However in this scenario, the 6.67 hr periodicity can only be interpreted as the rotation period of this strongly magnetized neutron star, which therefore represents the slowest pulsar ever detected, by orders of magnitude. We briefly discuss the viable slow-down scenarios, favoring a picture involving a period of fall-back accretion after the supernova explosion, similarly to what is invoked (although in a different regime) to explain the "anti-magnetar" scenario for other CCOs.

astro-ph.HE↗

arXiv2016

Mutually avoiding paths in random media and largests eigenvalues of random matrices

Recently, it was shown that the probability distribution function (PDF) of the free energy of a single continuum directed polymer (DP) in a random potential, equivalently of the height of a growing interface described by the Kardar-Parisi-Zhang (KPZ) equation, converges at large scale to the Tracy-Widom distribution.The latter describes the fluctuations of the largest eigenvalue of a random matrice, drawn from the Gaussian Unitary Ensemble (GUE), and the result holds for a DP with fixed endpoints, i.e. for the KPZ equation with droplet initial conditions. A more general conjecture can be put forward, relating the free energies of $N>1$ non-crossing continuum DP in a random potential, to the $N$-th largest eigenvalues of the GUE. Here, using replica methods, we provide an important test of this conjecture by calculating exactly the right tails of both PDF's and showing that they coincide for arbitrary $N$.

cond-mat.stat-mech↗

arXiv2016

The crossing probability for directed polymers in random media

We study the probability that two directed polymers in the same random potential do not intersect. We use the replica method to map the problem onto the attractive Lieb-Liniger model with generalized statistics between particles. We obtain analytical expressions for the first few moments of this probability, and compare them to a numerical simulation of a discrete model at high-temperature. From these observations, several large time properties of the non-crossing probabilities are conjectured. Extensions of our formalism to more general observables are discussed.

cond-mat.dis-nn↗

arXiv2016

Energy transport between two integrable spin chains

We study the energy transport in a system of two half-infinite XXZ chains initially kept separated at different temperatures, and later connected and let free to evolve unitarily. By changing independently the parameters of the two halves, we highlight, through bosonisation and time-dependent matrix-product-state simulations, the different contributions of low-lying bosonic modes and of fermionic quasi-particles to the energy transport. In the simulations we also observe that the energy current reaches a finite value which only slowly decays to zero. The general pictures that emerges is the following. Since integrability is only locally broken in this model, a pre-equilibration behaviour may appear. In particular, when the sound velocities of the bosonic modes of the two halves match, the low-temperature energy current is almost stationary and described by a formula with a non-universal prefactor interpreted as a transmission coefficient. Thermalisation, characterized by the absence of any energy flow, occurs only on longer time-scales which are not accessible with our numerics.

cond-mat.stat-mech↗

arXiv2016

Equilibration Properties of Classical Integrable Field Theories

We study the equilibration properties of classical integrable field theories at a finite energy density, with a time evolution that starts from initial conditions far from equilibrium. These classical field theories may be regarded as quantum field theories in the regime of high occupation numbers. This observation permits to recover the classical quantities from the quantum ones by taking a proper $\hbar \rightarrow 0$ limit. In particular, the time averages of the classical theories can be expressed in terms of a suitable version of the LeClair-Mussardo formula relative to the Generalized Gibbs Ensemble. For the purposes of handling time averages, our approach provides a solution of the problem of the {\em infinite gap solutions} of the Inverse Scattering Method.

cond-mat.stat-mech↗

arXiv2016

The tale of the two tails of the oldish PSR J2055+2539

We analyzed a deep {\it XMM-Newton} observation of the radio-quiet $γ$-ray PSR J2055+2539. The spectrum of the X-ray counterpart is non-thermal, with a photon index of $Γ$=2.36$\pm$0.14 (1$σ$ confidence). We detected X-ray pulsations with a pulsed fraction of (25$\pm$3)\% and a sinusoidal shape. Taking into account considerations on the $γ$-ray efficiency of the pulsar and on its X-ray spectrum, we can infer a pulsar distance ranging from 450 pc to 750 pc. We found two different nebular features associated to PSR J2055+2539 and protruding from it. The angle between the two nebular main axes is $\sim$ (162.8$\pm$0.7)$^{\circ}$. The main, brighter feature is 12' long and $<$20" thick, characterized by an asymmetry with respect to the main axis that evolves with the distance from the pulsar, possibly forming a helical pattern. The secondary feature is 250" $\times$ 30". Both nebulae present an almost flat brightness profile with a sudden decrease at the end. The nebulae can be fitted either by a power-law model or a thermal bremsstrahlung model. A plausible interpretation of the brighter nebula is in terms of a collimated ballistic jet. The secondary nebula is most likely a classical synchrotron-emitting tail.

astro-ph.HE↗

arXiv2016

Thermalization and many-body localization in systems under dynamic nuclear polarization

We study the role of dipolar interactions in the standard protocol used to achieve dynamic nuclear polarization (DNP). In the so-called spin-temperature regime, where the interactions establish an effective thermodynamic behavior in the out-of-equilibrium stationary state, we provide numerical predictions for the level of hyperpolarization. We show that nuclear spins equilibrate to the effective spin-temperature established among the electron spins of radicals, as expected from the quantum theory of thermalization. Moreover, we present an analytical technique to estimate the spin temperature, and thus, the nuclear hyperpolarization in the steady state, as a function of interaction strength and quenched disorder. This reproduces both our numerical data and experimental results. Our central finding is that the nuclear hyperpolarization increases steadily upon reducing the interaction strength (by diluting the radical density). Interestingly, the highest polarization is reached at a point where the establishment of a spin temperature is just about to break down due to the incipient many-body localization transition in the electron spin system.

cond-mat.str-el↗

arXiv2015

Results from DROXO IV. EXTraS discovery of an X-ray flare from the Class I protostar candidate ISO-Oph 85

X-ray emission from Young Stellar Objects (YSOs) is crucial to understand star formation. A very limited amount of X-ray results is available for the protostellar (ClassI) phase. A systematic search of transient X-ray phenomena combined with a careful evaluation of the evolutionary stage offer a widely unexplored window to our understanding of YSOs X-ray properties. Within the EXTraS project, a search for transients and variability in the whole XMM-Newton archive, we discover transient X-ray emission consistent with ISO-Oph 85, a strongly embedded YSO in the rho Ophiuchi region, not detected in previous time-averaged X-ray studies. We extract an X-ray light curve for the flare and determine its spectral parameters from XMM-Newton/EPIC (European Photon Imaging Camera) data using quantile analysis. The X-ray flare ($2500\,s$), the only one detected in the XMM-Newton archive for ISO-Oph 85, has a luminosity of $LogL_X[erg/s]=31.1$ and a spectrum consistent with a highly-absorbed one-component thermal model ($N_H=1.0^{+1.2}_{-0.5}10^{23}\,cm^{-2}$, $kT=1.15^{+2.35}_{-0.65}\,keV)$. We set an upper limit of $LogL_X[erg/s]<29.5$ to the quiescent X-ray luminosity. We build a SED with IR to mm photometry drawn from literature and mid-IR Spitzer and sub-mm Herschel photometry analysed by us, and compare it with pre-computed models. The sub-mm emission peak in the Herschel data suggests that the object is a ClassI protostar. However, the Herschel/IR position offset is larger than for other YSOs in the region, leaving some doubt on the association. This is the first X-ray flare from a YSO recognised as a candidate ClassI YSO via the analysis of its complete SED. This work shows how the analysis of the whole SED is fundamental for the classification of YSOs, and how the X-ray source detection techniques we developed can open a new era in time-resolved analysis of the X-ray emission from stars.

astro-ph.SR↗

arXiv2015

Crossing probability for directed polymers in random media: exact tail of the distribution

We study the probability $p \equiv p_η(t)$ that two directed polymers in a given random potential $η$ and with fixed and nearby endpoints, do not cross until time $t$. This probability is itself a random variable (over samples $η$) which, as we show, acquires a very broad probability distribution at large time. In particular the moments of $p$ are found to be dominated by atypical samples where $p$ is of order unity. Building on a formula established by us in a previous work using nested Bethe Ansatz and Macdonald process methods, we obtain analytically the leading large time behavior of {\it all moments} $\overline{p^m}\simeq γ_m/t$. From this, we extract the exact tail $\sim ρ(p)/t$ of the probability distribution of the non-crossing probability at large time. The exact formula is compared to numerical simulations, with excellent agreement.

cond-mat.stat-mech↗

arXiv2015

Dynamic nuclear polarization and the paradox of Quantum Thermalization

Dynamic Nuclear Polarization (DNP) is to date the most effective technique to increase the nuclear polarization up to a factor $100,000$ opening disruptive perspectives for medical applications. In DNP, the nuclear spins are driven to an - out of equilibrium - hyperpolarized state by microwave saturation of the electron spins in interaction with them. Here we show that the electron dipolar interactions compete with the local magnetic fields resulting in two distinct dynamical phases: for strong interactions the electron spins equilibrate to an extremely low effective temperature that boosts DNP efficiency. For weak interaction this spin temperature is not defined and the polarization profile has an 'hole burning' shape characteristic of the non interacting case. The study of the many-body eigenstates reveals that these two phases are intimately related to the problem of thermalization in closed quantum systems where breaking of ergodicity is expected varying the strength of the interactions.

cond-mat.str-el↗

arXiv2014

Stationary states in a free fermionic chain from the Quench Action Method

We employ the Quench Action Method (QAM) for a recently considered geometrical quantum quench: two free fermionic chains initially at different temperatures are joined together in the middle and let evolve unitarily with a translation invariant Hamiltonian. We show that two different stationary regimes are reached at long times, depending on the interplay between the observation time scale T and the total length L of the system. We show the emergence of a non-equilibrium steady state (NESS) supporting an energy current for observation time T much smaller than the system size L. We then identify a longer time-scale for which thermalization occurs in a Generalized Gibbs Ensemble (GGE).

cond-mat.stat-mech↗

arXiv2014

Quenching the magnetic flux in 1d fermionic ring: Loschmidt echo and edge singularity

We consider the non-equilibrium 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 non-trivial. 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 present 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.

cond-mat.stat-mech↗

arXiv2014

Energy transport in Heisenberg chains beyond the Luttinger liquid paradigm

We study the energy transport between two interacting spin chains which are initially separated, held at different temperatures and subsequently put in contact. We consider the spin-1/2 XXZ model in the gapless regime and exploit its integrability properties to formulate an analytical Ansatz for the non-equilibrium steady state even at temperatures where the low-energy Luttinger liquid description is not accurate. We apply our method to compute the steady energy current and benchmark it both with the known low-energy limit and at higher temperatures with numerical simulations. We find an excellent agreement even at high temperatures, where the Luttinger liquid prediction is shown to fail.

cond-mat.stat-mech↗

arXiv2013

Support set of random wave-functions on the Bethe lattice

We introduce a new measure of ergodicity, the support set $S_\varepsilon$, for random wave functions on disordered lattices. It is more sensitive than the traditional inverse participation ratios and their moments in the cases where the extended state is very sparse. We express the typical support set $S_{\varepsilon}$ in terms of the distribution function of the wave function amplitudes and illustrate the scaling of $S_{\varepsilon}\propto N^α$ with $N$ (the lattice size) for the most general case of the multi-fractal distribution. A number of relationships between the new exponent $α$ and the conventional spectrum of multi-fractal dimensions is established. These relationships are tested by numerical study of statistics of wave functions on disordered Bethe lattices. We also obtain numerically the finite-size spectrum of fractal dimensions on the Bethe lattice which shows two apparent fixed points as $N$ increases. The results allow us to conjecture that extended states on the Bethe lattice at all strengths of disorder below the localization transition are non-ergodic with a clear multifractal structure that evolves towards almost ergodic behavior in the clean limit.

cond-mat.stat-mech↗

arXiv2013

Non-equilibrium thermal transport in the quantum Ising chain

We consider two quantum Ising chains initially prepared at thermal equilibrium but with different temperatures and coupled at a given time through one of their end points. In the long-time limit the system reaches a non-equilibrium steady state. We discuss properties of this non-equilibrium steady state, and characterize the convergence to the steady regime. We compute the mean energy flux through the chain and the large deviation function for the quantum and thermal fluctuations of this energy transfer.

cond-mat.str-el↗

arXiv2013

Optical Polarimetry of the Inner Crab Nebula and Pulsar

Time-resolved polarisation measurements of pulsars offer an unique insight into the geometry of their emission regions. Such measure\ ments provide observational constraints on the different models proposed for the pulsar emission mechanisms. Optical polarisation data of the Crab Nebula was obtained from the HST archive. The data set consists of a series of observations of the nebula taken with the HST/ACS. We produced polarisation vector maps of the inner nebula and measured, for the first time, the degree of linear polarisation (P.D.) and the position angle (P.A.) of the pulsar's integrated pulse beam, and of its nearby synchrotron knot. This yielded $\rm P.D.=5.2\pm0.3%$ and $\rm P.A.=105.1\pm1.6\degr$ for the pulsar, and $\rm P.D.=59.0\pm1.9%$ and $\rm P.A.=124.7\pm1.0\degr$ for the synchrotron knot. This is the first high-spatial resolution multi-epoch study of the polarisation of the inner nebula and pulsar. None of the main features in the nebula show evidence of significant polarisation evolution in the period covered by these observations. The results for the pulsar are consistent with those obtained by Słowikowska et al (2009) using the high-time resolution photo-polarimeter OPTIMA, once the DC component has been subtracted. Our results clearly prove that the knot is the main source of the DC component.

astro-ph.HE↗

arXiv2013

Ergodicity breaking in a model showing many-body localization

We study the breaking of ergodicity measured in terms of return probability in the evolution of a quantum state of a spin chain. In the non ergodic phase a quantum state evolves in a much smaller fraction of the Hilbert space than would be allowed by the conservation of extensive observables. By the anomalous scaling of the participation ratios with system size we are led to consider the distribution of the wave function coefficients, a standard observable in modern studies of Anderson localization. We finally present a criterion for the identification of the ergodicity breaking (many-body localization) transition based on these distributions which is quite robust and well suited for numerical investigations of a broad class of problems.

cond-mat.str-el↗