Publications (82)182.34 Total impact

Article: Nonperturbative renormalization and running of Delta F=2 fourfermion operators in the SF scheme
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ABSTRACT: We present preliminary results of a nonperturbative study of the scaledependent renormalization constants of a complete basis of Delta F=2 parityodd fourfermion operators that enter the computation of hadronic Bparameters within the Standard Model (SM) and beyond. We consider nonperturbatively O(a) improved Wilson fermions and our gauge configurations contain two flavors of massless sea quarks. The mixing pattern of these operators is the same as for a regularization that preserves chiral symmetry, in particular there is a "physical" mixing between some of the operators. The renormalization group running matrix is computed in the continuum limit for a family of Schrodinger Functional (SF) schemes through finite volume recursive techniques. We compute nonperturbatively the relation between the renormalization group invariant operators and their counterparts renormalized in the SF at a low energy scale, together with the nonperturbative matching matrix between the lattice regularized theory and the various SF schemes.  [Show abstract] [Hide abstract]
ABSTRACT: We describe a new set of gauge configurations generated within the CLS effort. These ensembles have N_f=2+1 flavors of nonperturbatively improved Wilson fermions in the sea with the LuescherWeisz action used for the gluons. Open boundary conditions in time are used to address the problem of topological freezing at small lattice spacings and twistedmass reweighting for improved stability of the simulations. We give the bare parameters at which the ensembles have been generated and how these parameters have been chosen. Details of the algorithmic setup and its performance are presented as well as measurements of the pion and kaon masses alongside the scale parameter t_0. 
Article: Flavored tetraquark spectroscopy
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ABSTRACT: The recent confirmation of the charged charmonium like resonance Z(4430) by the LHCb experiment strongly suggests the existence of QCD multi quarks bound states. Some preliminary results about hypothetical flavored tetraquark mesons are reported. Such states are particularly amenable to Lattice QCD studies as their interpolating operators do not overlap with those of ordinary hiddencharm mesons.  [Show abstract] [Hide abstract]
ABSTRACT: We attempt a description of the recently discovered Z_{c,b} states in terms of Feshbach resonances arising from the interaction between the `closed' subspace of hadrocharmonium levels and the `open' one of opencharm/beauty thresholds. We show how the neutrality of the X(3872) might be understood in this scheme and provide a preliminary explanation of the pattern of the measured total widths of X,Z_{c,b}. 
Article: Renormalization of HQET $\Delta B=2$ operators: O($a$) improvement and $1/m$ matching with QCDM
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ABSTRACT: We determine a basis of dimension7 operators which arise at O($a$) in the Symanzik expansion of the $\Delta B=2$ operators with static heavy quarks. We consider both Wilsonlike and GinspargWilson light quarks. Exact chiral symmetry reduces the number of these O($a$) counterterms by a factor of two. Only a subset of these operators has previously appeared in the literature. We then extend the analysis to the O($1/m$) operators contributing beyond the static approximation.  [Show abstract] [Hide abstract]
ABSTRACT: The phenomenology of the socalled X, Y and Z hadronic resonances is hard to reconcile with standard charmonium or bottomonium interpretations. It has been suggested that some of these new hadrons can possibly be described as tightly bound tetraquark states and/or as loosely bound twomeson molecules. In the present paper we focus on the hypothetical existence of flavored, doubly charmed tetraquarks. Such states might also carry double electric charge, and in this case, if discovered, they could univocally be interpreted in terms of compact tetraquarks. Flavored tetraquarks are also amenable to lattice studies, as their interpolating operators do not overlap with ordinary meson ones. We show that doubly charmed tetraquarks could significantly be produced at the LHC from B_{c} or Ξ_{bc} heavy baryons. 

Article: Neutral meson oscillations in the Standard Model and beyond from Nf=2 Twisted Mass Lattice QCD
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ABSTRACT: We present the ETMC results for the bag parameters describing the neutral kaon mixing in the Standard Model and beyond and preliminary results for the bag parameters controlling the short distance contributions in the D^0\bar{D}^0 oscillations. We also present preliminary results for the B_{Bd}, B_{Bs}, B_{Bs}/B_{Bd} and \xi parameter controlling B^0_\bar{B}^0 oscillations in the Standard Model employing the socalled ratio method. Using Nf=2 maximally twisted sea quarks and OsterwalderSeiler valence quarks we achieve both O(a)improvement and continuum like renormalization pattern. Simulations are performed at threevalues of the lattice spacing and several values of quark masses in the light, strange, charm region and above charm up to ~2.5m_c. Our results are extrapolated to the continuum limit and extrapolated/interpolated to the physical quark masses.  [Show abstract] [Hide abstract]
ABSTRACT: We present the first unquenched, continuum limit, lattice QCD results for the matrix elements of the operators describing neutral kaon oscillations in extensions of the Standard Model. Owing to the accuracy of our calculation on \Delta S=2 weak Hamiltonian matrix elements, we are able to provide a refined Unitarity Triangle analysis improving the bounds coming from model independent constraints on New Physics. In our nonperturbative computation we use a combination of Nf=2 maximally twisted sea quarks and OsterwalderSeiler valence quarks in order to achieve both O(a)improvement and continuumlike renormalization properties for the relevant fourfermion operators. The calculation of the renormalization constants has been performed nonperturbatively in the RIMOM scheme. Based on simulations at four values of the lattice spacing and a number of quark masses we have extrapolated/interpolated our results to the continuum limit and physical light/strange quark masses.  [Show abstract] [Hide abstract]
ABSTRACT: The masses of the lowlying strange and charm baryons are evaluated using two degenerate flavors of twisted mass sea quarks for pion masses in the range of about 260 MeV to 450 MeV. The strange and charm valence quark masses are tuned to reproduce the mass of the kaon and Dmeson at the physical point. The treelevel Symanzik improved gauge action is employed. We use three values of the lattice spacing, corresponding to $\beta=3.9$, $\beta=4.05$ and $\beta=4.2$ with $r_0/a=5.22(2)$, $r_0/a=6.61(3)$ and $r_0/a=8.31(5)$ respectively. %spacings $a=0.0855(5)$ and $a=0.0667(3)$ determined from the pion decay constant. We examine the dependence of the strange and charm baryons on the lattice spacing and strange and charm quark masses. The pion mass dependence is studied and physical results are obtained using heavy baryon chiral perturbation theory to extrapolate to the physical point.  [Show abstract] [Hide abstract]
ABSTRACT: We present results on the electroweak form factors and on the lower moments of parton distributions of the nucleon, within lattice QCD using two dynamical flavors of degenerate twisted mass fermions. Results are obtained on lattices with three different values of the lattice spacings, namely a=0.089 fm, a=0.070 fm and a=0.056 fm, allowing the investigation of cutoff effects. The volume dependence is examined by comparing results on two lattices of spatial length L=2.1 fm and L=2.8 fm. The simulations span pion masses in the range of 260470 MeV. Our results are renormalized nonperturbatively and the values are given in the MSscheme at a scale mu=2 GeV.  [Show abstract] [Hide abstract]
ABSTRACT: We present preliminary results at {\beta} = 1.95 (a = 0.077 fm) on the first unquenched N_f=2+1+1 lattice computation of the B_K parameter which controls the neutral kaon oscillations in the Standard Model. Using N_f=2+1+1 maximally twisted sea quarks and OsterwalderSeiler valence quarks we achieve O(a) improvement and a continuumlike renormalization pattern for the fourfermion operator. Our results are extrapolated/interpolated to the physical light/strange quark mass but not yet to the continuum limit. The computation of the relevant renormalization constants is performed non perturbatively in the RI'MOM scheme using dedicated simulations with N_f=4 degenerate sea quark flavours produced by the ETM collaboration. We get B_K^{RGI} (a = 0.077) = 0.747(18), which when compared to our previous unquenched N_f=2 determination and most of the existing results, suggests a rather weak B_K^{RGI} dependence on the number of dynamical flavours. We are at the moment analysing lattice data at two additional {\beta} values which will allow us to perform an extrapolation to the continuum limit.  [Show abstract] [Hide abstract]
ABSTRACT: We present results on the lower moments of the nucleon generalized parton distri butions within lattice QCD using two dynamical flavors of degenerate twisted mass fermions. Our simulations are performed on lattices with three different values of the lattice spacings, namely $a=0.089$ fm, $a=0.070$ fm and $a=0.056$ fm, allowing the investigation of cutoff effects. The volume dependence is examined using simulations on two lattices of spatial length $L=2.1$ fm and $L=2.8$ fm. The simulations span pion masses in the range of 260470 MeV. Our results are renormalized nonperturbatively and the values are given in the $\bar{\rm MS}$ scheme at a scale $ \mu=2$ GeV. They are chirally extrapolated to the physical point in order to compare with experiment. The consequences of these results on the spin carried by the quarks in the nucleon are investigated.  [Show abstract] [Hide abstract]
ABSTRACT: We present results on the nucleon electromagnetic form factors within lattice QCD using two flavors of degenerate twisted mass fermions. Volume effects are examined using simulations at two volumes of spatial length L=2.1 fm and L=2.8 fm. Cutoff effects are investigated using three different values of the lattice spacings, namely a=0.089 fm, a=0.070 and a=0.056 fm. The nucleon magnetic moment, Dirac and Pauli radii are obtained in the continuum limit and chirally extrapolated to the physical pion mass allowing for a comparison with experiment.  [Show abstract] [Hide abstract]
ABSTRACT: We present first results on the octet and decuplet strange baryon spectrum with $N_f=2+1+1$ twisted mass quarks. We use an Osterwalder Seiler valence strange quark with a mass tuned to the kaon and compare the results with those obtained in the unitary setup. This comparison allows to perform a first study of the lattice artefacts introduced by the mixed action approach. We investigate the effect of the strange and charm quarks in the sea by using two lattice spacings and comparing with preceding $N_f = 2$ twisted mass fermion calculations. Comment: Contribution at the XXVIII International Symposium on Lattice Field Theory, Lattice2010, June 1419, 2010, Villasimius, Italy  [Show abstract] [Hide abstract]
ABSTRACT: We present preliminary results on the of neutral kaon oscillations in extensions of the Standard Model. Using Nf=2 maximally twisted sea quarks and OsterwalderSeiler valence quarks, we achieve both O(a)improvement and continuumlike renormalization pattern for the relevant fourfermion operators. We perform simulations at three values of the lattice spacing and extrapolate/interpolate our results to the continuum limit and physical light/strange quark mass. The calculation of the renormalization constants of the complete operator basis is performed non perturbatively in the RIMOM scheme. Comment: 7 pages, 2 figures; presented at the XXVIII International Symposium on Lattice Field Theory Villasimius, Sardinia, Italy  [Show abstract] [Hide abstract]
ABSTRACT: We compute the mass spectrum for strange/charmed baryons in the partially quenched approach using N_f=2 twisted mass QCD configurations. We investigate two main issues: the size of lattice artefacts using three values of the lattice spacing (the smallest of which is approximately 0.05 fm) and the dependence of baryon masses on meson (or quark) masses. We thus perform a global fit in order to extrapolate simultaneously to the continuum limit and to the physical point. We estimate the masses of Omega_{sss}, Xi_{dss}, Lambda_{uds}, Omega_{ccc}, Xi_{dcc}, Lambda_{udc}. Comment: Contribution at the XXVIII International Symposium on Lattice Field Theory, Lattice2010, June 1419, 2010, Villasimius, Italy  [Show abstract] [Hide abstract]
ABSTRACT: We present results on the nucleon form factors and moments of generalized parton distributions obtained within the twisted mass formulation of lattice QCD. We include a discussion of lattice artifacts by examining results at different volumes and lattice spacings. We compare our results with those obtained using different discretization schemes and to experiment. Comment: 4 pages, 3 Figures, Invited talk presented at the 35th International Conference of High Energy Physics  ICHEP 2010 July 2228, 2010, Paris, France 
Article: Geometrical Properties of TwoDimensional Interacting SelfAvoidingWalks at the ThetaPoint
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ABSTRACT: We perform a Monte Carlo simulation of twodimensional Nstep interacting selfavoiding walks at the theta point, with lengths up to N=3200. We compute the critical exponents, verifying the Coulombgas predictions, the thetapoint temperature T_theta = 1.4986(11), and several invariant size ratios. Then, we focus on the geometrical features of the walks, computing the instantaneous shape ratios, the average asphericity, and the endtoend distribution function. For the latter quantity, we verify in detail the theoretical predictions for its small and largedistance behavior.  [Show abstract] [Hide abstract]
ABSTRACT: We present results on the nucleon axial form factors within lattice QCD using two flavors of degenerate twisted mass fermions. Volume effects are examined using simulations at two volumes of spatial length $L=2.1$ fm and $L=2.8$ fm. Cutoff effects are investigated using three different values of the lattice spacings, namely $a=0.089$ fm, $a=0.070$ fm and $a=0.056$ fm. The nucleon axial charge is obtained in the continuum limit and chirally extrapolated to the physical pion mass enabling comparison with experiment.
Publication Stats
1k  Citations  
182.34  Total Impact Points  
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Institutions

20122014

Sapienza University of Rome
 Department of Physics
Roma, Latium, Italy 
Universidad Autónoma de Madrid
Madrid, Madrid, Spain


2011

University of Grenoble
Grenoble, RhôneAlpes, France


2010

University Joseph Fourier  Grenoble 1
 Laboratoire de Physique Subatomique et Cosmologie
Grenoble, RhôneAlpes, France


20072008

CERN
 Physics Department (PH)
Genève, Geneva, Switzerland


20062007

Università Degli Studi Roma Tre
 Department of Mathematics and Physics
Roma, Latium, Italy


2005

National Informatics Centre
New Dilli, NCT, India


19992002

Università di Pisa
 Department of Physics "E.Fermi"
Pisa, Tuscany, Italy


2000

Université ParisSud 11
 Laboratoire de Physique Théorique d'Orsay
Orsay, ÎledeFrance, France
