International School for Advanced Studies

About: International School for Advanced Studies is a education organization based out in Trieste, Friuli-Venezia Giulia, Italy. It is known for research contribution in the topics: Galaxy & Dark matter. The organization has 3751 authors who have published 13433 publications receiving 588454 citations. The organization is also known as: SISSA & Scuola Internazionale Superiore di Studi Avanzati.

Leading isospin breaking effects on the lattice

Abstract: We present a method to evaluate on the lattice the leading isospin breaking effects due to both the small mass difference between the up and down quarks and the QED interaction. Our proposal is applicable in principle to any $\mathrm{QCD}+\mathrm{QED}$ gauge invariant hadronic observable that can be computed on the lattice. It is based on the expansion of the path integral in powers of the small parameters $({\stackrel{^}{m}}_{d}\ensuremath{-}{\stackrel{^}{m}}_{u})/{\ensuremath{\Lambda}}_{\mathrm{QCD}}$ and ${\stackrel{^}{\ensuremath{\alpha}}}_{\mathrm{em}}$, where ${\stackrel{^}{m}}_{f}$ is the renormalized quark mass and ${\stackrel{^}{\ensuremath{\alpha}}}_{\mathrm{em}}$ the renormalized fine structure constant. In this paper we discuss in detail the general strategy of the method and the conventional, although arbitrary, separation of QCD from QED isospin breaking corrections. We obtain results for the pion mass splitting, ${M}_{{\ensuremath{\pi}}^{+}}^{2}\ensuremath{-}{M}_{{\ensuremath{\pi}}^{0}}^{2}=1.44(13)(16)\ifmmode\times\else\texttimes\fi{}{10}^{3}\text{ }\text{ }{\mathrm{MeV}}^{2}$, for the Dashen's theorem breaking parameter ${\ensuremath{\epsilon}}_{\ensuremath{\gamma}}=0.79(18)(18)$, for the light quark masses, $[{\stackrel{^}{m}}_{d}\ensuremath{-}{\stackrel{^}{m}}_{u}](\overline{\mathrm{MS}},2\text{ }\text{ }\mathrm{GeV})=2.39(8)(17)\text{ }\text{ }\mathrm{MeV}$, $[{\stackrel{^}{m}}_{u}/{\stackrel{^}{m}}_{d}](\overline{\mathrm{MS}},2\text{ }\text{ }\mathrm{GeV})=0.50(2)(3)$, and for the flavor symmetry breaking parameters $R$ and $Q$. We also update our previous results for the QCD isospin breaking corrections to the ${K}_{\ensuremath{\ell}2}$ decay rate and for the QCD contribution to the neutron-proton mass splitting. The numerical results of this paper have been obtained by using the gluon field configurations produced by the ETMC Collaboration with ${n}_{f}=2$ dynamical quarks. We treated the dynamical quarks as electrically neutral particles (electroquenched approximation) and neglected a disconnected diagram in the charged and neutral pion mass splitting. We provide all the formulas necessary to remove these approximations and discuss in detail the estimate of the associated systematic uncertainties.

Cosmic stellar relics in the Galactic halo

Abstract: We study the stellar population history and chemical evolution of the Milky Way (MW) in a hierarchical Λ cold dark matter model for structure formation. Using a Monte Carlo method based on the semi-analytical extended Press & Schechter formalism, we develop a new code GAlaxy MErger Treeand Evolution (gamete) to reconstruct the merger tree of the Galaxy and follow the evolution of gas and stars along the hierarchical tree. Our approach allows us to compare the observational properties of the MW with model results, exploring different properties of primordial stars, such as their initial mass function and the critical metallicity for low-mass star formation, Zcr. In particular, by matching our predictions to the metallicity distribution function (MDF) of metal-poor stars in the Galactic halo we find that: (i) a strong supernova (SN) feedback is required to reproduce the observed properties of the MW; (ii) stars with [Fe/H] 0 or the masses of the first stars mPopIII > 0.9 M⊙; (v) the statistical impact of truly second-generation stars, that is, stars forming out of gas polluted only by metal-free stars, is negligible in current samples; and (vi) independent of Zcr, 60 per cent of metals in the GM are ejected through winds by haloes with masses M < 6 × 109 M⊙, thus showing that low-mass haloes are the dominant population contributing to cosmic metal enrichment. We discuss the limitations of our study and comparison with previous work.

A realistic pattern of lepton mixing and masses from S_4 and CP

Abstract: We present a supersymmetric model with the flavour symmetry $$S_4 \times Z_3$$ and a CP symmetry which are broken to a $$Z_3$$ subgroup of the flavour symmetry in the charged lepton sector and to $$Z_2 \times $$ CP ( $$\times Z_3$$ ) in the neutrino one at leading order. This model implements an approach capable of predicting lepton mixing angles and Dirac as well as Majorana phases in terms of one free parameter. This parameter, directly related to the size of the reactor mixing angle $$\theta _{13}$$ , can be naturally of the correct order in our model. Atmospheric mixing is maximal, while $$\sin ^2 \theta _{12} \gtrsim 1/3$$ . All three phases are predicted: the Dirac phase is maximal, whereas the two Majorana phases are trivial. The neutrino mass matrix contains only three real parameters at leading order and neutrino masses effectively only depend on two of them. As a consequence, they have to be normally ordered and the absolute neutrino mass scale and the sum of the neutrino masses are predicted. The vacuum of the flavons can be correctly aligned. We study subleading corrections to the leading order results and show that they are small.

Delayed Upregulation of ATP P2X3 Receptors of Trigeminal Sensory Neurons by Calcitonin Gene-Related Peptide

Abstract: Recent evidence indicates a key role for the neuropeptide calcitonin gene-related peptide (CGRP) in migraine pain, as demonstrated by the strong analgesic action of CGRP receptor antagonists, although the mechanisms of this effect remain unclear. Most trigeminal nociceptive neurons releasing CGRP also express ATP-activated purinergic P2X3 receptors to transduce pain. To understand whether the CGRP action involves P2X3 receptor modulation, the model of trigeminal nociceptive neurons in culture was used to examine the long-term action of this peptide. Although 79% of CGRP-binding neurons expressed P2X3 receptors, acute application of CGRP did not change P2X3 receptor function. Nevertheless, after 1 h of CGRP treatment, strong enhancement of the amplitude of P2X3 receptor currents was observed together with accelerated recovery from desensitization. Receptor upregulation persisted up to 10 h (despite CGRP washout), was accompanied by increased P2X3 gene transcription, and was fully prevented by the CGRP antagonist CGRP8–37. Surface biotinylation showed CGRP augmented P2X3 receptor expression, consistent with confocal microscopy data indicating enhanced P2X3 immunoreactivity beneath the neuronal membrane. These results suggest that CGRP stimulated trafficking of P2X3 receptors to the cell-surface membrane. Using pharmacological tools, we demonstrated that this effect of CGRP was dependent on protein kinase A and PKC activation and was prevented by the trafficking inhibitor brefeldin A. Capsaicin-sensitive TRPV1 vanilloid receptors were not upregulated. The present data demonstrate a new form of selective, slow upregulation of nociceptive P2X3 receptors on trigeminal neurons by CGRP. This mechanism might contribute to pain sensitization and represents a model of neuronal plasticity in response to a migraine mediator.

Structural, bonding, dynamical, and electronic properties of liquid silicon: An ab initio molecular-dynamics study.

Abstract: We report an extensive first-principles molecular-dynamics study of metallic liquid silicon. Our description of the local order is in excellent agreement with x-ray- and neutron-diffraction experiments. The difference in internal energy between the simulated liquid phase and the crystal agrees well with the experimental enthalpy of melting. Analysis of the valence-electronic-charge density shows persistence of some covalent bonds in the melt. These bonds give rise in the power spectrum of the system dynamics to a well-identifiable feature associated with stretching vibrations. Unlike the case in the crystal, in the liquid the covalent bonds are continuously forming and breaking in response to atomic motion. The majority of bonds are broken on average, leading to fast diffusion and to metallic behavior of the melt. The calculated electronic conductivity shows good agreement with available experimental data.