Publications

Introduction: Erectile dysfunction is a highly prevalent condition. Existing guidelines provide recommendations for diagnosis and treatment, but they are often disregarded in clinical practice in favor of a “patient-tailored” approach. Objectives: We planned a Delphi consensus method to bridge the gap between evidence-based medicine and the real-life approach in daily practice. Materials and Methods: The Advisory Board prepared 15 statements on debated topics in andrology, each including 4–6 items designed as a 5-point Likert scale. After a validation phase, the questionnaire was sent by e-mail to a panel of experts for a first round of voting; members of the panel were later invited to a second round of voting, preceded by discussion of the “hot topics” identified in the first round. Results: The first round of the Delphi consensus involved 101 experts; 71 (70%) also took part in the second round of voting. The Advisory Board deemed 22 items to be worthy of debate, and these underwent the second round of voting. “Real-life” results from the survey proved quite different from evidence-based recommendations. Conclusion: Although guidelines suggest the best approach for a “standard” patient, real-life settings require flexibility. Diagnostic and therapeutic approaches should be tailored to the patients’ needs. Phosphodiesterase type 5 inhibitors are recognized as the first-line therapy in both settings, including the newly introduced sildenafil orodispersible film. Indications from the panel might help close the gap between recommendations from guidelines and real-life practice in relation to the diagnosis and treatment of erectile dysfunction. Isidori AM, Giammusso B, Corona G, et al. Diagnostic and Therapeutic Workup of Erectile Dysfunction: Results From a Delphi Consensus of Andrology Experts. Sex Med 2019;7:292–302.

Confinement properties of the 1+1 Schwinger model can be studied by computing the string tension between two charges. It is finite (vanishing) if the fermions are massive (massless), corresponding to the occurrence of confinement (screening). Motivated by the possibility of experimentally simulating the Schwinger model, we investigate here the robustness of its screened and confined phases. First, we analyze the effect of nearest-neighbor density-density interaction terms, which - in the absence of the gauge fields - give rise to the Thirring model. The resulting Schwinger-Thirring model (very often also referred to as the gauged Thirring model) is studied, also in presence of a topological θ-term, showing that the massless (massive) model remains screened (confined) and that there is deconfinement only for θ=±π in the massive case. Estimates of the parameters of the Schwinger-Thirring model are provided with a discussion of a possible experimental setup for its realization with ultracold atoms. The possibility that the gauge fields live in higher dimensions while the fermions remain in 1+1 is also considered. One may refer to this model as the pseudo-Schwinger-Thirring model. It is shown that the screening of external charges occurs for 2+1 and 3+1 gauge fields, exactly as it occurs in 1+1 dimensions, with a radical change of the long distance interaction induced by the gauge fields. The massive (massless) model continues to exhibit confinement (screening), signaling that it is the dimensionality of the matter fields, and not of the gauge fields, to determine confinement properties. A computation for the string tension is presented in perturbation theory. Our conclusion is that 1+1 models exhibiting confinement or screening - massless or massive, in the presence of a topological term or not - retain their main properties when the Thirring interaction is added or the gauge fields live in a higher dimension.

We study the role of electronic spin and valley symmetry in the quantum interference (QI) patterns of the transmission function in graphene quantum junctions. In particular, we link it to the position of the destructive QI antiresonances. When the spin or valley symmetry is preserved, electrons with opposite spin or valley display the same interference pattern. On the other hand, when a symmetry is lifted, the antiresonances are split, with a consequent dramatic differentiation of the transport properties in the respective channel. We demonstrate rigorously this link in terms of the analytical structure of the electronic Green function, which follows from the symmetries of the microscopic model, and we confirm the result with numerical calculations for graphene nanoflakes. We argue that this is a generic and robust feature that can be exploited in different ways for the realization of nanoelectronic QI devices, generalizing the recent proposal of a QI-assisted spin-filtering effect [A. Valli et al., Nano Lett. 18, 2158 (2018)10.1021/acs.nanolett.8b00453].

Unveiling the physics that governs the intertwining between the nanoscale self-organization and the dynamics of insulator-to-metal transitions (IMTs) is key for controlling on demand the ultrafast switching in strongly correlated materials and nanodevices. A paradigmatic case is the IMT in V2O3, for which the mechanism that leads to the nucleation and growth of metallic nanodroplets out of the supposedly homogeneous Mott insulating phase is still a mystery. Here, we combine x-ray photoemission electron microscopy and ultrafast nonequilibrium optical spectroscopy to investigate the early-stage dynamics of isolated metallic nanodroplets across the IMT in V2O3 thin films. Our experiments show that the low-temperature monoclinic antiferromagnetic insulating phase is characterized by the spontaneous formation of striped polydomains, with different lattice distortions. The insulating domain boundaries accommodate the birth of metallic nanodroplets, whose nonequilibrium expansion can be triggered by the photoinduced change of the 3d-orbital occupation. We address the relation between the spontaneous nanotexture of the Mott insulating phase in V2O3 and the timescale of the metallic seeds growth. We speculate that the photoinduced metallic growth can proceed along a nonthermal pathway in which the monoclinic lattice symmetry of the insulating phase is partially retained.

We introduce and study the properties of a periodic model interpolating between the sine-And the sinh-Gordon theories in 1 + 1 dimensions. This model shows the peculiarities, due to the preservation of the functional form of their potential across RG flows, of the two limiting cases: The sine-Gordon, not having conventional order/magnetization at finite temperature, but exhibiting Berezinskii-Kosterlitz-Thouless (BKT) transition; and the sinh-Gordon, not having a phase transition, but being integrable. The considered interpolation, which we term as sn-Gordon model, is performed with potentials written in terms of Jacobi functions. The critical properties of the sn-Gordon theory are discussed by a renormalization-group approach. The critical points, except the sinh-Gordon one, are found to be of BKT type. Explicit expressions for the critical coupling as a function of the elliptic modulus are given.

Inflationary cosmology represents a well-studied framework to describe the expansion of space in the early universe, as it explains the origin of the large-scale structure of the cosmos and the isotropy of the cosmic microwave background radiation. The recent detection of the Higgs boson renewed research activities based on the assumption that the inflaton could be identified with the Higgs field. At the same time, the question whether the inflationary potential can be extended to the electroweak scale and whether it should be necessarily chosen ad hoc in order to be physically acceptable are at the center of an intense debate. Here, we propose and perform the slow-roll analysis of the so-called Massive Natural Inflation (MNI) model which has three adjustable parameters, the explicit mass term, a Fourier amplitude u, and a frequency parameter β, in addition to a constant term of the potential. This theory has the advantage to present a structure of infinite non-degenerate minima and is amenable to an easy integration of high-energy modes. We show that, using PLANCK data, one can fix, in the large β-region, the parameters of the model in a unique way. We also demonstrate that the value for the parameters chosen at the cosmological scale does not influence the results at the electroweak scale. We argue that other models can have similar properties both at cosmological and electroweak scales, but with the MNI model one can complete the theory towards low energies and easily perform the integration of modes up to the electroweak scale, producing the correct order-of-magnitude for the Higgs mass.

In this paper we study an Ising spin chain with short-range competing interactions in the presence of long-range ferromagnetic interactions in the canonical ensemble. The simultaneous presence of the frustration induced by the short-range couplings together with their competition with the long-range term gives rise to a rich thermodynamic-phase diagram. We compare our results with the limit in which one of two local interactions is turned off, which was previously studied in the literature. Eight regions of parameters with qualitatively distinct properties are featured, with different first-and second-order phase transition lines and critical points.

After the publication of paper [1], we realized that the coefficients of the nonlinear terms in the generalized fractional Boussinesq differential equations were affected by an error generated by an incorrect application of the Fourier transform to the nonlinear terms of the equations of motion. For those terms, one has to proceed by redoing the corresponding calculations as in the Appendices B, C and D of Chendjou et al. [1]. In the lattice, before taking the continuum limit, one gets sums of the type [Formula presented]. Doing the approximation that in these sums the fields [Formula presented]'s are slowly varying in space, one can bring such terms [Formula presented] outside the sums over n′. We then obtain the same structure for the generalized fractional Boussinesq differential equations, but with different coefficients of their nonlinear terms. More precisely: • In Eq. (17), the coefficient [Formula presented] should read[Formula presented]• In Eq. (24), the coefficient [Formula presented] should read[Formula presented]• In Eq. (31), the coefficient [Formula presented] should read[Formula presented]Apart from the numerical values of the coefficients [Formula presented] [Formula presented] and [Formula presented] the conclusions of the paper remain unaltered. As a future work, we think that it could be interesting to release the approximation mentioned above for the continuum limit of the nonlinear terms and get a more general fractional equation. Finally, Hamiltonian (18) should read[Formula presented]with a factor fn,m added in the last sum on the right hand side. The equations of motions (19) and the subsequent conclusions are unaltered.

The possibility to exploit quantum coherence to strongly enhance the efficiency of charge transport in solid state devices working at ambient conditions would pave the way to disruptive technological applications. In this work, we tackle the problem of the quantum transport of photogenerated electronic excitations subject to dephasing and on-site Coulomb interactions. We show that the transport to a continuum of states representing metallic collectors can be optimized by exploiting the "superradiance" phenomena. We demonstrate that this is a coherent effect which is robust against dephasing and electron-electron interactions in a parameters range that is compatible with actual implementation in few-monolayer transition-metal-oxide (TMO) heterostructures.

We study the ground state entanglement entropy of the quantum Dyson hierarchical spin chain in which the interaction decays algebraically with the distance as r?1?We exploit the real-space renormalisation group solution which gives the ground-state wave function in the form of a tree tensor network and provides a manageable recursive expression for the reduced density matrix of the renormalised ground state. Surprisingly, we find that at criticality the entanglement entropy obeys an area law, as opposite to the logarithmic scaling of short-range critical systems and of other non-hierarchical long-range models. We provide also some analytical results in the limit of large and small that are tested against the numerical solution of the recursive equations.

We consider the entanglement Hamiltonian for an interval in a chain of free fermions in its ground state and show that the lattice expression goes over into the conformal one if one includes the hopping to distant neighbours in the continuum limit. For an infinite chain, this can be done analytically for arbitrary fillings and is shown to be the consequence of the particular structure of the entanglement Hamiltonian, while for finite rings or temperatures the result is based on numerical calculations.

Abstract: Given a quantum heat engine that operates in a cycle that reaches maximal efficiency for a time-dependent Hamiltonian H(τ) of the working substance, with overall controllable driving H(τ) = g(τ) H, we study the deviation of the efficiency from the optimal value due to a generic time-independent perturbation in the Hamiltonian. We show that for a working substance consisting of two two-level systems, by suitably tuning the interaction, the deviation can be suppressed up to the third order in the perturbation parameter – and thus almost retaining the optimality of the engine. Graphical abstract: [Figure not available: see fulltext.].

The interaction between ultrashort light pulses and non-absorbing materials is dominated by impulsive stimulated Raman scattering (ISRS). The description of ISRS in the context of pump&probe experiments is based on effective classical models describing the interaction between the phonon and pulsed electromagnetic fields. Here we report a theoretical description of ISRS where we do not make any semi-classical approximation and we treat both photonic and phononic degrees of freedom at the quantum level. The results of the quantum model are compared with semiclassical results and validated by means of spectrally resolved pump&probe measurements on α-quartz.

We consider quantum quenches in the integrable SU(3)-invariant spin chain (Lai Sutherland model), and focus on the family of integrable initial states. By means of a quantum transfer matrix approach, these can be related to solitonnon-preserving boundary transfer matrices in an appropriate transverse direction. In this work, we provide a technical analysis of such integrable transfer matrices. In particular, we address the computation of their spectrum: This is achieved by deriving a set of functional relations between the eigenvalues of certain fused operators that are constructed starting from the soliton-non-preserving boundary transfer matrices (namely the T-and Y-systems). As a direct physical application of our analysis, we compute the Loschmidt echo for imaginary and real times after a quench from the integrable states. Our results are also relevant for the study of the spectrum of SU(3)-invariant Hamiltonians with open boundary conditions.

We consider quantum quenches in the integrable SU(3)-invariant spin chain (Lai Sutherland model) which admits a Bethe ansatz description in terms of two different quasiparticle species, providing a prototypical example of a model solvable by nested Bethe ansatz. We identify infinite families of integrable initial states for which analytic results can be obtained. We show that they include special families of two-site product states which can be related to integrable soliton non-preserving boundary conditions in an appropriate rotated channel. We present a complete analytical result for the quasiparticle rapidity distribution functions corresponding to the stationary state reached at large times after the quench from the integrable initial states. Our results are obtained within a quantum transfer matrix (QTM) approach, which does not rely on the knowledge of the quasilocal conservation laws or of the overlaps between the initial states and the eigenstates of the Hamiltonian. Furthermore, based on an analogy with previous works, we conjecture analytic expressions for such overlaps: This allows us to employ the quench action method to derive a set of integral equations characterizing the quasi-particle distribution functions of the post-quench steady state. We verify that the solution to the latter coincides with our analytic result found using the QTM approach. Finally, we present a direct physical application of our results by providing predictions for the propagation of entanglement after the quench from such integrable states.

We consider the interaction-driven Mott transition at zero temperature from the viewpoint of microscopic Fermi liquid theory. To this end, we derive an exact expression for the Landau parameters within the dynamical mean-field theory (DMFT) approximation to the single-band Hubbard model. At the Mott transition, the symmetric and the antisymmetric Landau parameters diverge. The vanishing compressibility at the Mott transition directly implies the divergence of the forward-scattering amplitude in the charge sector, which connects the proximity of the Mott phase to a tendency toward phase separation. We verify the expected behavior of the Landau parameters in a DMFT application to the Hubbard model on the triangular lattice at finite temperature. Exact conservation laws and the Ward identity are crucial to capture vertex divergences related to the Mott transition. We furthermore generalize Leggett's formula for the static susceptibility of the Fermi liquid to the static fermion-boson response function. In the charge sector, the limits of small transferred momentum and frequency of this response function commute at the Mott transition.

We employ martingale theory to describe fluctuations of entropy production for open quantum systems in nonequilbrium steady states. Using the formalism of quantum jump trajectories, we identify a decomposition of entropy production into an exponential martingale and a purely quantum term, both obeying integral fluctuation theorems. An important consequence of this approach is the derivation of a set of genuine universal results for stopping-time and infimum statistics of stochastic entropy production. Finally, we complement the general formalism with numerical simulations of a qubit system.

I will review the possibility to retrieve nonlinear responses in complex materials by measuring noise correlations of classical and quantum nature.

The dissociation of excitons into a liquid of holes and electrons in photoexcited semiconductors, despite being one of the first recognized examples of a Mott transition, still defies a complete understanding, especially regarding the nature of the transition, which is found to be continuous in some cases and discontinuous in others. Here we consider an idealized model of photoexcited semiconductors that can be mapped onto a spin-polarized half-filled Hubbard model, whose phase diagram reproduces most of the phenomenology of those systems and uncovers the key role of the exciton binding energy in determining the nature of the exciton Mott transition. We find indeed that the transition changes from discontinuous to continuous as the binding energy increases. Moreover, we uncover a rather anomalous electron-hole liquid phase next to the transition, which still sustains excitonic excitations despite being a degenerate Fermi liquid of heavy mass quasiparticles.

We further elaborate on the device proposed by Karimi et al. [15], in which coupled superconducting qubits can play the role of a quantum heat switch. In the present paper we analyze the performances of the switch if the number of qubits increases considering in details the cases of three and four qubits. To this aim we study the effect of the number of qubits on the transmitted power between baths. As the number of qubits increases, the transmitted power between baths increases as well.