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R. Romano

Publications and source records attributed to R. Romano.

18 recordsLinked to original sources
arXiv2020

Extended Lipkin-Meshkov-Glick Hamiltonian

The Lipkin-Meshkov-Glick (LMG) model was devised to test the validity of different approximate formalisms to treat many-particle systems. The model was constructed to be exactly solvable and yet non-trivial, in order to capture some of the main features of real physical systems. In the present contribution, we explicitly review the fact that different many-body approximations commonly used in different fields in physics clearly fail to describe the exact LMG solution. With similar assumptions as those adopted for the LMG model, we propose a new Hamiltonian based on a general two-body interaction. The new model (Extended LMG) is not only more general than the original LMG model and, therefore, with a potentially larger spectrum of applicability, but also the physics behind its exact solution can be much better captured by common many-body approximations. At the basis of this improvement lies a new term in the Hamiltonian that depends on the number of constituents and polarizes the system; the associated symmetry breaking is discussed, together with some implications for the study of more realistic systems.

nucl-th↗
arXiv2014

Collapse Models and Perceptual Processes

Theories including a collapse mechanism have been presented various years ago. They are based on a modification of standard quantum mechanics in which nonlinear and stochastic terms are added to the evolution equation. Their principal merits derive from the fact that they are mathematically precise schemes accounting, on the basis of a unique universal dynamical principle, both for the quantum behavior of microscopic systems as well as for the reduction associated to measurement processes and for the classical behavior of macroscopic objects. Since such theories qualify themselves not as new interpretations but as modifications of the standard theory they can be, in principle, tested against quantum mechanics. Recently, various investigations identifying possible crucial test have been discussed. In spite of the extreme difficulty to perform such tests it seems that recent technological developments allow at least to put precise limits on the parameters characterizing the modifications of the evolution equation. Here we will simply mention some of the recent investigations in this direction, while we will mainly concentrate our attention to the way in which collapse theories account for definite perceptual process. The differences between the case of reductions induced by perceptions and those related to measurement procedures by means of standard macroscopic devices will be discussed. On this basis, we suggest a precise experimental test of collapse theories involving conscious observers. We make plausible, by discussing in detail a toy model, that the modified dynamics can give rise to quite small but systematic errors in the visual perceptual process.

quant-ph↗
arXiv2013

On a quite recent proposal of faster than light quantum communication

In a recent paper, Kalamidas has advanced a new proposal of faster than light communication which has not yet been proved invalid. In this paper we show that, as all previous proposals, it does not work. The mistake arises from an inappropriate use of some approximations.

quant-ph↗
arXiv2009

Age and Extinction of the Ultraviolet Emitting Regions in M82

The M82 galaxy has been the subject of several studies basically because it is relatively close to to the Milky Way and it displays a strong star formation activity. Using multi-band images of M82 we have determined the age and extinction of the stellar population located in regions with strong UV emission, these region are in the nucleus and the disk of M82. We also have employed the UV images of M82 and the physical properties of its stellar clusters to measure the contribution of the clusters to the detected UV flux. We found that clusters located in the nuclear regions are emitting all the observed UV flux, whereas clusters of the disk emit less than ~10%. Based on the results obtained from this work we can infer that the field stars located in the disk of M82 could have been part of a stellar cluster when they were born.

astro-ph.CO↗
arXiv2008

Stellar disks of Collisional Ring Galaxies I. New multiband images, Radial intensity and color profiles, and confrontation with N-body simulations

We present new multi-band imaging data in the optical (BVRI and Halpha) and near infrared bands (JHK) of 15 candidate ring galaxies from the sample of Appleton & Marston (1997). We use these data to obtain color composite images, global magnitudes and colors of both the ring galaxy and its companion(s), and radial profiles of intensity and colors. We find that only nine of the observed galaxies have multi-band morphologies expected for the classical collisional scenario of ring formation, indicating the high degree of contamination of the ring galaxy sample by galaxies without a clear ring morphology. The radial intensity profiles, obtained by masking the off-centered nucleus, peak at the position of the ring, with the profiles in the continuum bands broader than that in the Halpha line. The images as well as the radial intensity and color profiles clearly demonstrate the existence of the pre-collisional stellar disk outside the star-forming ring, which is in general bluer than the disk internal to the ring. The stellar disk seems to have retained its size, with the disk outside the ring having a shorter exponential scale length as compared to the values expected in normal spiral galaxies of comparable masses. The rings in our sample of galaxies are found to be located preferentially at around half-way through the stellar disk. The most likely reason for this preference is bias against detecting rings when they are close to the center (they would be confused with the resonant rings), and at the edge of the disk the gas surface density may be below the critical density required for star formation. Most of the observed characteristics point to relatively recent collisions (<80 Myr ago) according to the N-body simulations of Gerber et al. (1996).

astro-ph↗
arXiv2008

HST/ACS imaging of M82: A comparison of mass and size distribution functions of the younger nuclear and older disk clusters

We present the results obtained from an objective search for stellar clusters, both in the currently active nuclear starburst region, and in the post-starburst disk of M82. Images obtained with the HST/ACS in F435W(B), F555W(V), and F814W(I) filters were used in the search for the clusters. We detected 653 clusters of which 393 are located outside the central 450 pc in the post-starburst disk of M82. The luminosity function of the detected clusters show an apparent turnover at B=22 mag (M_B=-5.8), which we interpret from Monte Carlo simulations as due to incompleteness in the detection of faint clusters, rather than an intrinsic log-normal distribution. We derived a photometric mass of every detected cluster from models of simple stellar populations assuming a mean age of either an 8 (nuclear clusters) or 100 (disk clusters) million years old. The mass functions of the disk (older) and the nuclear (younger) clusters follow power-laws, the former being marginally flatter (alpha=1.5+/-0.1) than the latter (alpha=1.8+/-0.1). The distribution of sizes (Full Width at Half Maximum) of clusters brighter than the apparent turn-over magnitude (mass>2E+4 Mo) can be described by a log-normal function. This function peaks at 10 pc for clusters more massive than 1E+5 Mo, whereas for lower masses, the peak is marginally shifted to larger values for the younger, and smaller values for the older clusters. The observed trend towards flattening of the mass function with age, together with an over-abundance of older compact clusters, imply that cluster disruption in M82 is both dependent on the mass and size of the clusters.

astro-ph↗
arXiv2007

Are the compact star clusters in M82 evolving towards globular clusters?

Recent HST/ACS images of M82 covering the entire galaxy have been used to detect star clusters. The galaxy is known to contain a young population (age < 10 Myr) in its starburst nucleus, surrounded by a post-starburst disk of age < 1 Gyr. We detect more than 650 star clusters in this galaxy, nearly 400 of them in the post-starburst disk. These data have been used to derive the luminosity, mass and size functions separately for the young nuclear, and intermediate-age disk clusters. In this contribution, we discuss the evolutionary status of these clusters, especially, on the chances of some of these clusters surviving to become old globular clusters.

astro-ph↗
arXiv2007

How to Find More Supernovae with Less Work: Object Classification Techniques for Difference Imaging

We present the results of applying new object classification techniques to difference images in the context of the Nearby Supernova Factory supernova search. Most current supernova searches subtract reference images from new images, identify objects in these difference images, and apply simple threshold cuts on parameters such as statistical significance, shape, and motion to reject objects such as cosmic rays, asteroids, and subtraction artifacts. Although most static objects subtract cleanly, even a very low false positive detection rate can lead to hundreds of non-supernova candidates which must be vetted by human inspection before triggering additional followup. In comparison to simple threshold cuts, more sophisticated methods such as Boosted Decision Trees, Random Forests, and Support Vector Machines provide dramatically better object discrimination. At the Nearby Supernova Factory, we reduced the number of non-supernova candidates by a factor of 10 while increasing our supernova identification efficiency. Methods such as these will be crucial for maintaining a reasonable false positive rate in the automated transient alert pipelines of upcoming projects such as PanSTARRS and LSST.

astro-ph↗
arXiv2005

Incoherent control and entanglement for two-dimensional coupled systems

We investigate accessibility and controllability of a quantum system S coupled to a quantum probe P, both described by two-dimensional Hilbert spaces, under the hypothesis that the external control affects only P. In this context accessibility and controllability properties describe to what extent it is possible to drive the state of the system S by acting on P and using the interaction between the two systems. We give necessary and sufficient conditions for these properties and we discuss the relation with the entangling capability of the interaction between S and P. In particular, we show that controllability can be expressed in terms of the SWAP operator, acting on the composite system, and its square root.

quant-ph↗
arXiv2005

Further results on the observability of quantum systems under general measurement

In this paper, we present a collection of results on the observability of quantum mechanical systems, in the case the output is the result of a discrete nonselective measurement. By defining an effective observable we extend previous results, on the Lie algebraic characterization of observable systems, to general measurements. Further results include the characterization of a `best probe' (i.e. a minimally disturbing probe) in indirect measurement and a study of the relation between disturbance and observability in this case. We also discuss how the observability properties of a quantum system relate to the problem of state reconstruction. Extensions of the formalism to the case of selective measurements are also given.

quant-ph↗
arXiv2005

The detection of non-thermal radio continuum spokes and the study of star formation in the Cartwheel

New sensitive Very Large Array 20 cm continuum observations of the Cartwheel, the prototypical collisional ring galaxy, were carried out with the principal aim of tracing supernova remnants that are expected to lie in the wake of the expanding ring and in the ring itself. We detect predominantly non-thermal radio continuum emission from regions associated with 13 ring HII complexes. The emission interior to the ring is confined to structures that resemble spokes of the wheel. The spokes start near bright HII complexes, and extend to around 6 arcsec (4 kpc) inward in the direction of the geometrical center of the ring. There is no apparent positional coincidence between the radio continuum and optical spokes. Radial distribution of intensity along the spokes suggests that the past star formation rate (SFR) in the Cartwheel was much lower than the current SFR. New Halpha observations were used to revise the current SFR in the Cartwheel. The revised value is 18 Msun/yr, which is a factor of 4 lower than the value reported previously, but is in good agreement with the SFR estimated from far infrared luminosity. About 30% of the observed 20 cm continuum non-thermal emission seems to originate in processes that are not related to star formation. Revised SFR in the Cartwheel is comparable to that in the rest of the ring galaxies.

astro-ph↗
arXiv2003

Complete positivity and dissipative factorized dynamics: some comments

After reviewing the main properties of time-evolutions of open quantum systems, some considerations about the positivity of factorized Markovian dynamics for bipartite systems are made. In particular, it is shown that the positivity of the whole time-evolution in general does not ask for the complete positivity of the single system time-evolutions, if they are allowed to differ. However, they must be completely positive if one is a small perturbation of the other, which is the typical situation for open systems in a heat bath.

quant-ph↗
arXiv2003

Neutral kaons in random media

The generalized dynamics describing the propagation of neutral kaons in randomly fluctuating media is derived and analyzed. It takes into account possible matter-induced effects leading to loss of phase coherence and dissipation. The study of selected neutral kaon observables indicates that these non-standard effects are amenable to a direct experimental analysis.

hep-ph↗
arXiv2003

An open quantum system approach to the B-mesons system

In this talk we consider a non standard evolution for the neutral B-mesons system, namely, an evolution in the open quantum systems framework. Such approach is justified by the very high sensitivity of experiments studying CP-violating phenomena in the B-mesons sector, very near to the one required to test some possible scenarios induced by quantum gravity at the Planck scale, whose effects at low energy can be described by a heat bath. We adopt a phenomenological point of view, introducing six new parameters that fully describe this kind of evolution without referring to a specific model for the microscopic interaction. We outline the main differences between this approach and the usual one in the description of evolution and decay of single mesons or correlated pairs.

hep-ph↗
arXiv2002

Complete positivity and entangled degrees of freedom

We study how some recently proposed noncontextuality tests based on quantum interferometry are affected if the test particles propagate as open systems in presence of a gaussian stochastic background. We show that physical consistency requires the resulting markovian dissipative time-evolution to be completely positive.

quant-ph↗
arXiv2001

Irreversibility and dissipation in neutral B-meson decays

The propagation and decay of neutral B-mesons can be described in terms of quantum dynamical semigroups; they provide generalized time-evolutions that take into account possible non-standard effects leading to loss of phase coherence and dissipation. These effects can be fully parametrized in terms of six phenomenological constants. A detailed analysis of selected B-meson decays shows that present and future dedicated experiments, both at colliders and B-factories, will be able to put stringent bounds on these non-standard parameters.

hep-ph↗
arXiv1994

Nonclassical Light in Interferometric Measurements

It is shown that the even and odd coherent light and other nonclassical states of light like superposition of coherent states with different phases may replace the squeezed light in interferometric gravitational wave detector to increase its sensitivity. (Contribution to the Second Workshop on Harmonic Oscillator, Cocoyoc, Mexico, March 1994)

hep-th↗