1,287 research outputs found
Instantons, diquarks and non-leptonic weak decays of hyperons
This work is devoted to the study of the non-perturbative contributions in
non-leptonic hyperon decays. We show that the instanton-induced 't Hooft
interaction can naturally explain the Delta I=1/2 rule, by generating
quark-diquark clustering inside octet baryons. We compute P-wave and S-wave
amplitudes in the Instanton Liquid Model (ILM), and find good agreement with
experiment. We propose a model-independent procedure to test on the lattice if
the leading quark-quark attraction in the 0^+ anti-triplet channel responsible
for diquark structures in hadrons is originated by the interaction generated by
quasi-classical fields or it is predominantly due to other perturbative and/or
confining forces.Comment: Final version to appear on PR
Thermodynamics of a three-flavor nonlocal Polyakov--Nambu--Jona-Lasinio model
The present work generalizes a nonlocal version of the Polyakov loop-extended
Nambu and Jona-Lasinio (PNJL) model to the case of three active quark flavors,
with inclusion of the axial U(1) anomaly. Gluon dynamics is incorporated
through a gluonic background field, expressed in terms of the Polyakov loop.
The thermodynamics of the nonlocal PNJL model accounts for both chiral and
deconfinement transitions. Our results obtained in mean-field approximation are
compared to lattice QCD results for quark flavors. Additional
pionic and kaonic contributions to the pressure are calculated in random phase
approximation. Finally, this nonlocal 3-flavor PNJL model is applied to the
finite density region of the QCD phase diagram. It is confirmed that the
existence and location of a critical point in this phase diagram depends
sensitively on the strength of the axial U(1) breaking interaction.Comment: 31 pages, 15 figures, minor changes compared to v
Thermodynamics and quark susceptibilities: a Monte-Carlo approach to the PNJL model
The Monte-Carlo method is applied to the Polyakov-loop extended
Nambu--Jona-Lasinio (PNJL) model. This leads beyond the saddle-point
approximation in a mean-field calculation and introduces fluctuations around
the mean fields. We study the impact of fluctuations on the thermodynamics of
the model, both in the case of pure gauge theory and including two quark
flavors. In the two-flavor case, we calculate the second-order Taylor expansion
coefficients of the thermodynamic grand canonical partition function with
respect to the quark chemical potential and present a comparison with
extrapolations from lattice QCD. We show that the introduction of fluctuations
produces only small changes in the behavior of the order parameters for chiral
symmetry restoration and the deconfinement transition. On the other hand, we
find that fluctuations are necessary in order to reproduce lattice data for the
flavor non-diagonal quark susceptibilities. Of particular importance are pion
fields, the contribution of which is strictly zero in the saddle point
approximation
Quantum field theories on the Lefschetz thimble
In these proceedings, we summarize the Lefschetz thimble approach to the sign
problem of Quantum Field Theories. In particular, we review its motivations,
and we summarize the results of the application of two different algorithms to
two test models.Comment: contributions to 31st International Symposium on Lattice Field Theory
- LATTICE 2013, July 29 - August 3, 2013, Mainz, Germany and QCD-TNT-III, 2-6
September, 2013, European Centre for Theoretical Studies in Nuclear Physics
and Related Areas (ECT*), Villazzano, Trento (Italy
Instantons, Chiral Dynamics and Hadronic Resonances
We use the Interacting Instanton Liquid Model (IILM) as a tool to study the
role played by the chiral interactions in the lowest-lying vector and axial
vector meson resonances. We find that narrow a1 and rho meson resonances can be
generated by instanton-induced chiral forces, even in the absence of
confinement. In the IILM, these hadrons are found to have masses only about 30%
larger than the experimental value and small width <10-50 MeV. This result
suggests that chiral interactions are very important in these systems and
provide most of their mass. We explore the decaying patterns of the rho meson,
in the absence of confinement. We argue that, in our model where only chiral
forces are switched on, this meson decays dissociating into its quark
anti-quark constituents
An efficient method to compute the residual phase on a Lefschetz thimble
We propose an efficient method to compute the so-called residual phase that
appears when performing Monte Carlo calculations on a Lefschetz thimble. The
method is stochastic and its cost scales linearly with the physical volume,
linearly with the number of stochastic estimators and quadratically with the
length of the extra dimension along the gradient flow. This is a drastic
improvement over previous estimates of the cost of computing the residual
phase. We also report on basic tests of correctness and scaling of the code.Comment: New simulations, new plot, new appendix added. To appear in PRD. 9
pages, 3 figure
Are There Diquarks in the Nucleon?
This work is devoted to the study of diquark correlations inside the nucleon.
We analyze some matrix elements which encode information about the
non-perturbative forces, in different color anti-triplet diquark channels. We
suggest a lattice calculation to check the quark-diquark picture and clarify
the role of instanton-mediated interactions. We study in detail the physical
properties of the 0+ diquark, using the Random Instanton Liquid Model. We find
that instanton forces are sufficiently strong to form a diquark bound-state,
with a mass of ~500 MeV, which is compatible with earlier estimates. We also
compute its electro-magnetic form factor and find that the diquark is a broad
object, with a size comparable with that of the proton.Comment: Final version, accepted for publication on Phys. Rev.
Light Hadron Spectrum in the Instanton Liquid Model
We review our recent study of the role played by the chiral interactions
induced by instantons, in the lowest-lying sector of the light hadron spectrum.
We discuss how the ordering of the lowest meson and baryon excitations is
explained by the structure of the instanton-induced quark-quark and gluon-gluon
interaction. We focus on the pion, nucleon, vector- and axial-vector mesons,
and on the scalar glueball. We find that all these hadrons are bound in this
model and have realistic masses.Comment: 8 pages, talk given at "Hadron 07", XII International Conference on
Hadron Spectroscopy, Frascati, October 8-13, 200
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