arXiv subjects

Sasa Prelovsek

Publications and source records attributed to Sasa Prelovsek.

At least 73 records · Page 4Linked to original sources

arXiv2010

Lattice searches for tetraquarks and mesonic molecules: light scalar mesons and XYZ states

Searches for tetraquarks and mesonic molecules in lattice QCD are briefly reviewed. In the light quark sector the most serious candidates are the lightest scalar resonances sigma, kappa, a0 and f0. In the hidden-charm sector I discuss lattice simulations of X(3872), Y(4260), Y(4140) and Z^+(4430). The most serious challenge in all these lattice studies is the presence of scattering states in addition to possible tetraquark/molecular states. The available methods for distinguishing both are reviewed and the main conclusions of the simulations are presented.

hep-lat↗

arXiv2009

Pion wave function from lattice QCD vs. chiral quark models

We analyze the equal-time Bethe-Salpeter quark wave function of the pion obtained from a quenched lattice QCD calculation with delocalized quark interpolators. We find that the result agrees remarkably well with the predictions of the Nambu--Jona-Lasinio model in all channels. We choose the quenched lattice QCD, since it is closer to the large-Nc limit of the Nambu--Jona-Lasinio model. We also show how transversity information, relevant for the light-cone physics, can be obtained from our equal-time rest-frame lattice calculations.

hep-ph↗

arXiv2008

A lattice study of light scalar tetraquarks

The observed mass pattern of scalar resonances below 1 GeV gives preference to the tetraquark assignment over the conventional $\bar qq$ assignment for these states. We present a search for tetraquarks with isospins 0, 1/2, 1 in lattice QCD, where the isospin channels 1/2 and 1 have not been studied before. We determine three energy levels in each isospin channel using the variational method. The scattering states and possible tetraquark states are distinguished by considering the volume-dependence of spectral weights and by considering the time-dependence of correlators near t~T/2. We find no indication for light tetraquarks at our range of pion masses 344-576 MeV.

hep-lat↗

arXiv2008

A lattice study of light scalar tetraquarks with isopins 0, 1/2 and 1

The observed mass pattern of scalar resonances below 1 GeV gives preference to the tetraquark assignment over the conventional $\bar qq$ assignment for these states. We present a search for tetraquarks with isospins 0,1/2,1 in lattice QCD, where isospin channels 1/2 and 1 have not been studied before. Our simulation uses Chirally Improved fermions on quenched gauge configurations. We determine three energy levels for each isospin using the variational method. The ground state is consistent with the scattering state, while the two excited states have energy above 2 GeV. Therefore we find no indication for light tetraquarks at our range of pion masses 344-576 MeV.

hep-lat↗

arXiv2008

Derivative sources in lattice spectroscopy of excited light-quark mesons

We construct efficient interpolating fields for lattice spectroscopy of mesons by applying covariant derivatives on Jacobi smeared quark sources. These interpolators are tested in a quenched calculation of excited mesons based on the variational method. We present results for pseudoscalar, scalar, vector and pseudovector mesons.

hep-lat↗

arXiv2008

Simulations of light scalar mesons on the lattice and related difficulties

I review the lattice simulations of light scalar mesons with quark-antiquark and tetraquark interpolating fields. Several difficulties which complicate the extraction of scalar meson masses from the scalar correlators are pointed out. One of the major difficulties is the presence of the two-pseudoscalar scattering states, which often dominate the correlator at light quark masses. In the simulations with unphysical approximations such scattering contributions are even more disturbing since they are often large and sometimes negative. Techniques which allow extraction of scalar meson masses in presence of scattering states are listed. Preliminary results of various lattice collaborations are presented.

hep-lat↗

arXiv2007

Meson spectroscopy with derivative quark sources

We present results for masses of light mesons obtained with the variational method using an enhanced basis of interpolating field operators with different quark smearings. The interpolators are constructed from Jacobi-smeared quarks of a Gaussian type as well as from derivative quark sources obtained by a covariant derivative acting on the Gaussian sources. For our analysis we use quenched gauge configurations with Chirally Improved quarks and the Luescher-Weisz gauge action on a 16^3 x 32 lattice with a = 0.148 fm. We discuss the influence of derivative sources on the overlap with excited states.

hep-lat↗

arXiv2007

Scalar Meson Spectroscopy with Lattice Staggered Fermions

With sufficiently light up and down quarks the isovector ($a_0$) and isosinglet ($f_0$) scalar meson propagators are dominated at large distance by two-meson states. In the staggered fermion formulation of lattice quantum chromodynamics, taste-symmetry breaking causes a proliferation of two-meson states that further complicates the analysis of these channels. Many of them are unphysical artifacts of the lattice approximation. They are expected to disappear in the continuum limit. The staggered-fermion fourth-root procedure has its purported counterpart in rooted staggered chiral perturbation theory (rSXPT). Fortunately, the rooted theory provides a strict framework that permits the analysis of scalar meson correlators in terms of only a small number of low energy couplings. Thus the analysis of the point-to-point scalar meson correlators in this context gives a useful consistency check of the fourth-root procedure and its proposed chiral realization. Through numerical simulation we have measured correlators for both the $a_0$ and $f_0$ channels in the ``Asqtad'' improved staggered fermion formulation in a lattice ensemble with lattice spacing $a = 0.12$ fm. We analyze those correlators in the context of rSXPT and obtain values of the low energy chiral couplings that are reasonably consistent with previous determinations.

hep-lat↗

arXiv2007

Updated constraints on new physics in rare charm decays

Motivated by recent experimental results on charm physics we investigate implications of the updated constraints of new physics in rare charm meson decays. We first reconsider effects of the MSSM in $c\to u γ$ constrained by the recent experimental evidence on $Δm_D$ and find, that due to the dominance of long distance physics, $D \to V γ$ decay rates cannot be modified by MSSM contributions. Then we consider effects of the extra heavy up vector-like quark models on the decay spectrum of $D^+ \to π^+ l^+ l^-$ and $D_s^+ \to K^+ l^+ l^-$ decays. We find a possibility for the tiny increase of the differential decay rate in the region of large dilepton mass. The R-parity violating supersymmetric model can also modify short distance dynamics in $c \to u l^+ l^-$ decays. We constrain relevant parameters using current upper bound on the $D^+ \to π^+ l^+ l^-$ decay rate and investigate impact of that constraint on the $D_s^+ \to K^+ l^+ l^-$ differential decay dilepton distribution. Present bounds still allow small modification of the standard model differential decay rate distribution.

hep-ph↗

arXiv2007

D Physics

Recently a lot of new experimental results on open charm hadrons have appeared. In particular many D meson resonances have been discovered. We discuss strong decays of positive and negative parity charmed mesons within heavy meson chiral perturbation theory and study the impact of excited charm states on the determination of the effective meson couplings. Motivated by recent experimental results we also reconsider semileptonic D to P l nu and D to V l nu decays within a model which combines heavy quark symmetry and properties of the chiral Lagrangian. Using limits of soft collinear effective theory and heavy quark effective theory we parametrize the semileptonic form factors. We include excited charm meson states in our Lagrangians and determine their impact on the charm meson semileptonic form factors. In some scenarios of new physics an up-like heavy quark appears, which induces FCNC at tree level for the c to u Z transitions. We investigate FCNC effects in D rare decays in particular the c to u l+ l- transition which might occur in D+ to pi+ l+ l- and D0 to rho0 l+ l-.

hep-ph↗

arXiv2006

Search for New Physics in Rare D Decays

In many extensions of the standard model an additional up-like heavy quark appears. Its appearance induces flavour changing neutral current transition in the up-quark region at the tree level. We investigate possible effects of these models in the c->u l+ l- transitions. First we determine impact of new physics on the relevant Wilson coefficients and then we reevaluate the standard model long-distance contributions. We calculate differential branching ratio for the D+ -> pi+ l+ l- and D0 -> rho0 l+ l- decays. Among all D decay modes these two are the simplest ones for the experimental studies. We also determine the forward-backward asymmetry for the D0 -> rho0 l+ l- decay and we comment on the effects of the Littlest Higgs model in both decay modes.

hep-ph↗

arXiv2006

Effects of Littlest Higgs model in rare D meson decays

A tree-level flavor changing neutral current in the up-like quark sector appears in one of the variations of the Littlest Higgs model. We investigate the effects of this coupling in the D+ -> pi+ l+ l- and D0 -> rho0 l+ l- decays, which are the most appropriate candidates for the experimental studies. However, the effects are found to be too small to be observed in the current and the foreseen experimental facilities. These decays are still dominated by the standard model long-distance contributions, which are reevaluated based on the new experimental input.

hep-ph↗

arXiv2005

Scalar mesons on the Lattice

The simulations of the light scalar mesons on the lattice are presented at the introductory level. The methods for determining the scalar meson masses are described. The problems related to some of these methods are presented and their solutions discussed.

hep-ph↗

arXiv2004

On the mass differences between the scalar and pseudoscalar heavy-light mesons

We discuss the recent experimental observation which suggested that the mass difference between the scalar and pseudoscalar heavy-light mesons is larger for the non-strange states than for the strange ones. After computing the chiral corrections in the heavy quark limit we show that, contrary to experiment, the mass difference in the non-strange case should be smaller.

hep-ph↗

arXiv2003

Chiral corrections and lattice QCD results for fBs/fBd and (Delta ms/Delta md)

It has been argued recently that the inclusion of the chiral logarithms in extrapolation of the lattice data can shift the value of the hadronic parameter xi = (fBs sqrt(B_{Bs}))/(fBd sqrt(B_{Bd})), from 1.16(6) to 1.32(10) and even higher. If true, that would considerably change the theoretical estimate for the ratio of oscillation frequencies in the neutral Bs- and Bd-systems, and would affect the standard CKM unitarity triangle analysis. In this letter we show that (fBs/fBd) \approx (fK/fpi), and thus the uncertainty due to the missing chiral logs is smaller than previously thought. By combining the NLO chiral expansion with the static heavy quark limit we obtain xi = 1.22(8).

hep-ph↗

arXiv2003

B --> pi and B --> K transitions in partially quenched chiral perturbation theory

We study the properties of the B-->pi and B-->K transition form factors in partially quenched QCD by using the approach of partially quenched chiral perturbation theory combined with the static heavy quark limit. We show that the form factors change almost linearly when varying the value of the sea quark mass, whereas the dependence on the valence quark mass contains both the standard and chirally divergent (quenched) logarithms. A simple strategy for the chiral extrapolations in the lattice studies with Nsea=2 is suggested. It consists of the linear extrapolations from the realistically accessible quark masses, first in the sea and then in the valence quark mass. From the present approach, we estimate the uncertainty induced by such extrapolations to be within 5%.

hep-lat↗

arXiv2003

B-->pi and B-->K transitions in standard and quenched chiral perturbation theory

We study the effects of chiral logs on the heavy-->light pseudoscalar meson transition form factors by using standard and quenched chiral perturbation theory combined with the static heavy quark limit. The resulting expressions are used to indicate the size of uncertainties due to the use of the quenched approximation in the current lattice studies. They may also be used to assess the size of systematic uncertainties induced by missing chiral log terms in extrapolating toward the physical pion mass. We also provide the coefficient multiplying the quenched chiral log, which may be useful if the quenched lattice studies are performed with very light mesons.

hep-lat↗

arXiv2001

Probing new physics in rare charm processes

We explore the sensitivity of the flavour changing neutral currents among c and u quarks in the context of the Minimal Supersymmetric Standard Model. The standard model rate for c->u gamma can be enhanced by up to two orders of magnitudes in general MSSM, while the c->ul^+l^- rate can be enhanced by at most a factor of three. The most suitable hadronic observable to probe the c->u gamma transition is the decay B_c->B_u^* gamma or the difference in decay rates of D^0->rho^0 gamma and D^0->omega gamma, since they are relatively free of the long distance contributions. The c ->ul^+l^- transition may be probed in D ->pi l^+l^- decays at high high di-lepton mass and we predict the long distance contributions for these modes.

hep-ph↗