Wed·Sep 21, 2005Wednesday·September 21, 2005

1. 01*

   Chiral extrapolation of hyperon vector form factors

   D. Guadagnoli🇮🇹 · V. Lubicz🇮🇹 · G. Martinelli🇮🇹 · M. Papinutto🇩🇪 · S. Simula🇮🇹 · G. Villadoro🇮🇹

   We present a new study of SU(3)-breaking corrections in hyperon vector form factors relevant for the extraction of Vus. A lattice quenched simulation has been performed, showing that it is possible to reach the required precision to extract SU(3)-breaking corrections in the regime of simulated masses. In order to perform the chiral extrapolation we calculated the chiral corrections to the vector form factor in HBChPT. Besides the one-loop O(p^2) contribution, we included also the subleading O(p^3) and O(1/M_B) corrections that, due to the Ademollo-Gatto theorem, are free from the contamination of unknown low energy constants. The results complete and correct previous calculations, and show that subleading corrections cannot be neglected. We also studied decuplet contributions within HBChPT and show that, in this case, the chiral expansion breaks down, rising doubts on the consistency of the theory.

   hep-lathep-phPoS(2006)·9 citations
2. 02*

   On meson spectral functions at high temperature and nonzero momentum

   Gert Aarts🇬🇧 · Simon Hands🇬🇧 · Seyong Kim🇰🇷 · Jose M. Martinez Resco🇨🇦

   In the high-temperature phase of QCD meson spectral functions at nonzero momentum are expected to have a nontrivial and interesting structure. In order to provide a reference point for lattice studies employing e.g. the Maximal Entropy Method, we discuss several characteristics of meson spectral functions in the infinite-temperature limit. We report on ongoing work in quenched QCD with staggered fermions.

   hep-lathep-phPoS(2006)·5 citations
3. 03*

   Large-N_f behavior of the Yukawa model: analytic results

   Sergio Caracciolo🇮🇹 · Bortolo Matteo Mognetti🇮🇹 · Andrea Pelissetto🇮🇹

   We investigate the Yukawa model in which $N_f$ fermions are coupled with a scalar field $\varphi$ through a Yukawa interaction. The phase diagram is rather well understood. If the fermions are massless, there is a chiral transition at $T_c$: for $T<T_c$ chiral symmetry is spontaneously broken. At $N_f=\infty$ the transition is mean-field like, while, for any finite $N_f$, standard arguments predict Ising behavior. This apparent contradiction has been explained by Kogut et al., who showed by scaling arguments and Monte Carlo simulations that in the large-$N_f$ limit the width of the Ising critical region scales as a power of $1/N_f$, so that only mean-field behavior is observed for $N_f$ strictly equal to infinity. We will show how the results of Kogut et al. can be recovered analytically in the framework of a generalized $1/N_f$ expansion. The method we use is a simple generalization of the method we have recently applied to a two-dimensional generalized Heisenberg model.

   hep-latPoS(2006)·5 citations
4. 04*

   Lowest Order Hadronic Contribution to the Muon g-2

   Christopher Aubin🇺🇸 · Tom Blum🇺🇸

   We present the most recent lattice results for the lowest-order hadronic contribution to the muon anomalous magnetic moment using 2+1 flavor improved staggered fermions. A precise fit to the low-q^2 region of the vacuum polarization is necessary to accurately extract the muon g-2. To obtain this fit, we use staggered chiral perturbation theory with the inclusion of the vector particles as resonances, to evaluate the vacuum polarization. We discuss the preliminary fit results and attendant systematic uncertainties, paying particular attention to the relative contributions of the pions and vector mesons.

   hep-latPoS(2006)·15 citations
5. 05*

   Critical behavior of two-dimensional fully frustrated XY systems

   Martin Hasenbusch🇮🇹 · Andrea Pelissetto🇮🇹 · Ettore Vicari🇮🇹

   We study the phase diagram of the two-dimensional fully frustrated XY model (FFXY) and of two related models, a lattice discretization of the Landau-Ginzburg-Wilson Hamiltonian for the critical modes of the FFXY model, and a coupled Ising-XY model. We present Monte Carlo simulations on square lattices $L\times L$, $L\lesssim 10^3$. We show that the low-temperature phase of these models is controlled by the same line of Gaussian fixed points as in the standard XY model. We find that, if a model undergoes a unique transition by varying temperature, then the transition is of first order. In the opposite case we observe two very close transitions: a transition associated with the spin degrees of freedom and, as temperature increases, a transition where chiral modes become critical. If they are continuous, they belong to the Kosterlitz-Thouless and to the Ising universality class, respectively. Ising and Kosterlitz-Thouless behavior is observed only after a preasymptotic regime, which is universal to some extent. In the chiral case, the approach is nonmonotonic for most observables, and there is a wide region in which finite-size scaling is controlled by an effective exponent ${\nu }_{\mathrm{eff}}\approx 0.8$. This explains the result $\nu \approx 0.8$ of many previous studies using smaller lattices.

   ↳ cond-mat.stat-mechcond-mat.supr-conhep-latJ.Phys.Conf.Ser.(2006)·2 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.