The High Density Region of QCD from an Effective Model

We study the high density region of QCD within an effective model obtained in the frame of the hopping parameter expansion and choosing Polyakov-type loops as the main dynamical variables representing the fermionic matter. This model still shows the so-called sign problem, a difficulty peculiar to non-zero chemical potential, but it permits the development of algorithms which ensure a good overlap of the simulated Monte Carlo ensemble with the true one. We review the main features of the model and present results concerning the dependence of various observables on the chemical potential and on the temperature, in particular of the charge density and the Polykov loop susceptibility, which may be used to characterize the various phases expected at high baryonic density. In this way, we obtain information about the phase structure of the model and the corresponding phase transitions and cross over regions, which can be considered as hints about the behaviour of non-zero density QCD.Comment: 7 pages, 5 figures, talk presented at the XXVth International Symposium on Lattice Field Theory, July 30 - August 4 2007, Regensburg, German

Neutron Star instabilities in full General Relativity using a Γ=2.75\Gamma=2.75 ideal fluid

We present results about the effect of the use of a stiffer equation of state, namely the ideal-fluid $\Gamma=2.75$ ones, on the dynamical bar-mode instability in rapidly rotating polytropic models of neutron stars in full General Relativity. We determine the change on the critical value of the instability parameter $\beta$ for the emergence of the instability when the adiabatic index $\Gamma$ is changed from 2 to 2.75 in order to mimic the behavior of a realistic equation of state. In particular, we show that the threshold for the onset of the bar-mode instability is reduced by this change in the stiffness and give a precise quantification of the change in value of the critical parameter $\beta_c$. We also extend the analysis to lower values of $\beta$ and show that low-beta shear instabilities are present also in the case of matter described by a simple polytropic equation of state.Comment: 16 pages, 16 figure

Modeling Mergers of Known Galactic Systems of Binary Neutron Stars

We present a study of the merger of six different known galactic systems of binary neutron stars (BNS) of unequal mass with a mass ratio between $0.75$ and $0.99$. Specifically, these systems are J1756-2251, J0737-3039A, J1906+0746, B1534+12, J0453+1559 and B1913+16. We follow the dynamics of the merger from the late stage of the inspiral process up to $\sim$ 20 ms after the system has merged, either to form a hyper-massive neutron star (NS) or a rotating black hole (BH), using a semi-realistic equation of state (EOS), namely the seven-segment piece-wise polytropic SLy with a thermal component. For the most extreme of these systems ($q=0.75$, J0453+1559), we also investigate the effects of different EOSs: APR4, H4, and MS1. Our numerical simulations are performed using only publicly available open source code such as, the Einstein Toolkit code deployed for the dynamical evolution and the LORENE code for the generation of the initial models. We show results on the gravitational wave signals, spectrogram and frequencies of the BNS after the merger and the BH properties in the two cases in which the system collapse within the simulated time.Comment: 13 pages, 10 figure

Spectral analysis of gravitational waves from binary neutron star merger remnants

In this work we analyze the gravitational wave signal from hypermassive neutron stars formed after the merger of binary neutron star systems, focusing on its spectral features. The gravitational wave signals are extracted from numerical relativity simulations of models already considered by De Pietri et al. [Phys. Rev. D 93, 064047 (2016)], Maione et al. [Classical Quantum Gravity 33, 175009 (2016)], and Feo et al. [Classical Quantum Gravity 34, 034001 (2017)], and allow us to study the effect of the total baryonic mass of such systems (from $2.4 M_{\odot}$ to $3 M_{\odot}$), the mass ratio (up to $q = 0.77$), and the neutron star equation of state, both in equal and highly unequal mass binaries. We use the peaks we find in the gravitational spectrum as an independent test of already published hypotheses of their physical origin and empirical relations linking them with the characteristics of the merging neutron stars. In particular, we highlight the effects of the mass ratio, which in the past was often neglected. We also analyze the temporal evolution of the emission frequencies. Finally, we introduce a modern variant of Prony's method to analyze the gravitational wave postmerger emission as a sum of complex exponentials, trying to overcome some drawbacks of both Fourier spectra and least-squares fitting. Overall, the spectral properties of the postmerger signal observed in our simulation are in agreement with those proposed by other groups. More specifically, we find that the analysis of Bauswein and Stergioulas [Phys. Rev. D 91, 124056 (2015)] is particularly effective for binaries with very low masses or with a small mass ratio and that the mechanical toy model of Takami et al. [Phys. Rev. D 91, 064001 (2015)] provides a comprehensive and accurate description of the early stages of the postmerger.Comment: 19 pages, 6 figure

Study of dynamical supersymmetry breaking for the two dimensional lattice Wess-Zumino model

A new approach to the study of the transition point in a class of two dimensional Wess-Zumino models is presented. The method is based on the calculation of rigorous lower bounds on the ground state energy density in the infinite lattice limit. Such bounds are useful in the discussion of supersymmetry phase transition. The transition point is then determined and compared with recent results based on large-scale Green Function Monte Carlo simulations with good agreement.Comment: 4 pages, 1 figure, Talk presented at Quark Confinement and the Hadron Spectrum VI, Villasimius, Sardinia, Italy, September 21-25, 200

Dynamical supersymmetry breaking and phase diagram of the lattice Wess-Zumino model

We study dynamical supersymmetry breaking and the transition point by non-perturbative lattice techniques in a class of two-dimensional N=1 Wess-Zumino model. The method is based on the calculation of rigorous lower bounds on the ground state energy density in the infinite-lattice limit. Such bounds are useful in the discussion of supersymmetry phase transition. The transition point is determined with this method and then compared with recent results based on large-scale Green Function Monte Carlo simulations with good agreement.Comment: 6 pages, 4 figs. Lattice2005 (theory), uses Po

The high density region of QCD in a large mass and chemical potential model

We study the high density region of QCD within an effective model obtained in the frame of the hopping parameter expansion. The model still acknowledges the sign problem peculiar to non-zero chemical potential, but it permits the development of refined algorithms which ensure a good overlap of the Monte Carlo ensemble with the true one. We review the main features of the model, including the most explicit form of the resumed expansion, and present calculations concerning the dependence of various observables on the chemical potential and on the temperature, in particular of the charge density and the diquark susceptibility, which may be used to characterize the various phases expected at high baryonic density.Comment: 6 pages, 5 figures, Lattice'05 proceedings, PoS styl

Stiffness effects on the dynamics of the bar-mode instability of Neutron Stars in full General Relativity

We present results on the effect of the stiffness of the equation of state on the dynamical bar-mode instability in rapidly rotating polytropic models of neutron stars in full General Relativity. We determine the change in the threshold for the emergence of the instability for a range of the adiabatic $\Gamma$ index from 2.0 to 3.0, including two values chosen to mimic more realistic equations of state at high densities.Comment: 12 pages, 5 figures. arXiv admin note: substantial text overlap with arXiv:1403.806

Exosome mediated communication in cancer: melanoma and sarcoma models

Exosomes (EXOs) are nanovesicles of diameter ranging between 50 to 140 nm, distinguished from other cell-derived vesicles by their origin, size, morphology and composition. Their stimulatory or inhibitory signaling activities are mediated by their content (mRNAs, microRNAs and proteins) that can be transferred from the cells of origin to recipient cells, influencing the surrounding microenvironment besides cell behavior. In this study we investigated EXO-mediated communications in two cancer models, melanoma and Ewing’s sarcoma. In view of our previous results demonstrating miR-221&222 as key factors for melanoma development and dissemination, we demonstrated that the EXO-mediated horizontal transfer of miR-222 was competent to deliver miR-222-associated properties increasing tumor malignancy. Melanoma-purified vesicles were characterized and investigated for the functionality of miR-222 in EXO-mediated tumorigenesis. Our data showed that EXOs secreted by miR-222-overexpressing cells induced a protumorigenic program in target cells, mainly through the upmodulation of the PI3K/AKT pathway. The reverse effects were obtained with EXOs recovered after inhibition of endogenous miR-221 and miR-222 by antagomir transfections. The possible differential significance of PI3K/AKT blockade in miR-222-transduced vs control cells was assessed by using BKM120, a pan inhibitor of PI3K. Results showed the capability of miR-222 overexpression to overcome BKM120-dependent effects. We then demonstrated the role of Ewing’s sarcoma-derived EXOs as mediators of signals involved in cancer growth, metastases and differentiation. Ewing’s sarcoma (EWS) is an aggressive childhood bone tumor characterized in the majority of cases by the presence of the fusion oncoprotein EWS-FLI1 and by high expression of the membrane glycoprotein CD99. These features, which are the necessary conditions for the pathogenesis of EWS, mediate tumor progression and maintain the cells in a dedifferentiated state. We evaluated the ability of EXOs, expressing or not CD99, to modulate the phenotype of EWS cells. We observed that the delivery of EXOs devoid of CD99 was sufficient to induce neural differentiation in EWS recipient cells through the inhibition of Notch-NF-kB signaling mediated by miR-34a overexpression. All together these observations would provide a significant step toward new biomarker discovery and innovative therapeutic options. These data on one side support miR-222 responsibility in the exosome-associated melanoma properties, on the other the role of CD99-shRNA/miR-34a-derived EXOs to induce differentiation in EWS, thus further indicating microRNAs as potential diagnostic, prognostic and eventually therapeutic biomarkers

Merger of compact stars in the two-families scenario

We analyse the phenomenological implications of the two-families scenario on the merger of compact stars. That scenario is based on the coexistence of both hadronic stars and strange quark stars. After discussing the classification of the possible mergers, we turn to detailed numerical simulations of the merger of two hadronic stars, i.e., "first family" stars in which delta resonances and hyperons are present, and we show results for the threshold mass of such binaries, for the mass dynamically ejected and the mass of the disk surrounding the post-merger object. We compare these results with those obtained within the one-family scenario and we conclude that relevant signatures of the two-families scenario can be suggested, in particular: the possibility of a rapid collapse to a black hole for masses even smaller than the ones associated to GW170817; during the first milliseconds, oscillations of the postmerger remnant at frequencies higher than the ones obtained in the one-family scenario; a large value of the mass dynamically ejected and a small mass of the disk, for binaries of low total mass. Finally, based on a population synthesis analysis, we present estimates of the number of mergers for: two hadronic stars; hadronic star - strange quark star; two strange quark stars. We show that for unequal mass systems and intermediate values of the total mass, the merger of a hadronic star and a strange quark star is very likely (GW170817 has a possible interpretation into this category of mergers). On the other hand, mergers of two strange quark stars are strongly suppressed.Comment: 18 pages, 16 figure