1,206 research outputs found
Unquenched Numerical Stochastic Perturbation Theory
The inclusion of fermionic loops contribution in Numerical Stochastic
Perturbation Theory (NSPT) has a nice feature: it does not cost so much
(provided only that an FFT can be implemented in a fairly efficient way).
Focusing on Lattice SU(3), we report on the performance of the current
implementation of the algorithm and the status of first computations
undertaken.Comment: 3 pages, 3 figures, Lattice2002(algor
Two and three loops computations of renormalization constants for lattice QCD
Renormalization constants can be computed by means of Numerical Stochastic
Perturbation Theory to two/three loops in lattice perturbation theory, both in
the quenched approximation and in the full (unquenched) theory. As a case of
study we report on the computation of renormalization constants of the
propagator for Wilson fermions. We present our unquenched (N_f=2) computations
and compare the results with non perturbative determinations.Comment: Lattice2004(improv), 3 pages, 4 figure
3-d lattice SU(3) free energy to four loops
We report on the perturbative computation of the 3d lattice Yang-Mills free
energy to four loops by means of Numerical Stochastic Perturbation Theory. The
known first and second orders have been correctly reproduced; the third and
fourth order coefficients are new results and the known logarithmic IR
divergence in the fourth order has been correctly identified. Progress is being
made in switching to the gluon mass IR regularization and the related inclusion
of the Faddeev-Popov determinant.Comment: Lattice2004(non-zero), 3 pages, 2 figure
Robust probabilistic-constrained optimization for IRS-aided MISO communication systems
Taking into account imperfect channel state information, this letter formulates and solves a joint active/passive beamforming optimization problem in multiple-input single-output systems with the support of an intelligent reflecting surface. In particular, we introduce an optimization problem to minimize the total transmit power subject to maintaining the users' signal-to-interference-plus-noise-ratio coverage probability above a predefined target. Due to the presence of probabilistic constraints, the proposed optimization problem is non-convex. To circumvent this issue, we first recast the proposed problem in a convex form by adopting the Bernstein-type inequality, and we then introduce a converging alternating optimization approach to iteratively find the active/passive beamforming vectors. In particular, the transformed robust optimization problem can be effectively solved by using standard interior-point methods. Numerical results demonstrate the effectiveness of jointly optimizing the active/passive beamforming vectors
B Physics on the Lattice: , , , , mixing, \fb and all that
We present a short review of our most recent high statistics lattice
determinations in the HQET of the following important parameters in B physics:
the B--meson binding energy, and the kinetic energy of the
b quark in the B meson, , which due to the presence of power
divergences require a non--perturbative renormalization to be defined; the
running mass of the b quark,
; the -- mass splitting, whose
value in the HQET is determined by the matrix element of the chromo--magnetic
operator between B meson states, ; the B parameter of the
-- mixing, , and the decay constant of the B meson,
. All these quantities have been computed using a sample of gauge
field configurations on a lattice at . For
and , we obtain our
estimates by combining results from three independent lattice simulations at
, and on the same volume.Comment: 3 latex pages, uses espcrc2.sty (included). Talk presented at
LATTICE96(heavy quarks
Renormalization of infrared contributions to the QCD pressure
Thanks to dimensional reduction, the infrared contributions to the QCD
pressure can be obtained from two different three-dimensional effective field
theories, called the Electrostatic QCD (Yang-Mills plus adjoint Higgs) and the
Magnetostatic QCD (pure Yang-Mills theory). Lattice measurements have been
carried out within these theories, but a proper interpretation of the results
requires renormalization, and in some cases also improvement, i.e. the removal
of terms of O(a) or O(a^2). We discuss how these computations can be
implemented and carried out up to 4-loop level with the help of Numerical
Stochastic Perturbation Theory.Comment: 7 pages, 4 figures, talk presented at Lattice 2006 (High temperature
and density
The leading non-perturbative coefficient in the weak-coupling expansion of hot QCD pressure
Using Numerical Stochastic Perturbation Theory within three-dimensional pure
SU(3) gauge theory, we estimate the last unknown renormalization constant that
is needed for converting the vacuum energy density of this model from lattice
regularization to the MSbar scheme. Making use of a previous non-perturbative
lattice measurement of the plaquette expectation value in three dimensions,
this allows us to approximate the first non-perturbative coefficient that
appears in the weak-coupling expansion of hot QCD pressure.Comment: 16 pages. v2: published versio
3-d Lattice QCD Free Energy to Four Loops
We compute the expansion of the 3-d Lattice QCD free energy to four loop
order by means of Numerical Stochastic Perturbation Theory. The first and
second order are already known and are correctly reproduced. The third and
fourth order coefficients are new results. The known logarithmic divergence in
the fourth order is correctly identified. We comment on the relevance of our
computation in the context of dimensionally reduced finite temperature QCD.Comment: 8 pages, 3 figures, latex typeset with JHEP3.cl
Four loop stochastic perturbation theory in 3d SU(3)
Dimensional reduction is a key issue in finite temperature field theory. For
example, when following the QCD Free Energy from low to high scales across the
critical temperature, ultrasoft degrees of freedom can be captured by a 3d
SU(3) pure gauge theory. For such a theory a complete perturbative matching
requires four loop computations, which we undertook by means of Numerical
Stochastic Perturbation Theory. We report on the computation of the pure gauge
plaquette in 3d, and in particular on the extraction of the logarithmic
divergence at order g^8, which had already been computed in the continuum.Comment: 3 pages, 2 figure, Lattice2003(nonzero
Towards 4-loop NSPT result for a 3-dimensional condensate-contribution to hot QCD pressure
Thanks to dimensional reduction, the contributions to the hot QCD pressure
coming from so-called soft modes can be studied via an effective
three-dimensional theory named Electrostatic QCD (spatial Yang-Mills fields
plus an adjoint Higgs scalar). The poor convergence of the perturbative series
within EQCD suggests to perform lattice measurements of some of the associated
gluon condensates. These turn out, however, to be plagued by large
discretization artifacts. We discuss how Numerical Stochastic Perturbation
Theory can be exploited to determine the full lattice spacing dependence of one
of these condensates up to 4-loop order, and sharpen our tools on a concrete
2-loop example.Comment: Presented at 25th International Symposium on Lattice Field Theory,
Regensburg, Germany, 30 Jul - 4 Aug 2007, 7 page
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