4,285 research outputs found
O(a^2) cutoff effects in lattice Wilson fermion simulations
In this paper we propose to interpret the large discretization artifacts
affecting the neutral pion mass in maximally twisted lattice QCD simulations as
O(a^2) effects whose magnitude is roughly proportional to the modulus square of
the (continuum) matrix element of the pseudoscalar density operator between
vacuum and one-pion state. The numerical size of this quantity is determined by
the dynamical mechanism of spontaneous chiral symmetry breaking and turns out
to be substantially larger than its natural magnitude set by the value of
Lambda_QCD.Comment: 38 pages, 1 figure, 2 table
A-term inflation and the MSSM
The parameter space for A-term inflation is explored with . With p=6 and \lambda_p~1, the observed spectrum and
spectral tilt can be obtained with soft mass of order 10^2 GeV but not with a
much higher mass. The case p=3 requires \lambda_p~10^{-9} to 10^{-12}. The
ratio m/A requires fine-tuning, which may be justified on environmental
grounds. An extension of the MSSM to include non-renormalizable terms and/or
Dirac neutrino masses might support either A-term inflation or modular
inflation.Comment: 10 pages, 3 figures; Comments added, typos correcte
Phase Structure of the 5D Abelian Higgs Model with Anisotropic Couplings
We establish the phase diagram of the five-dimensional anisotropic Abelian
Higgs model by mean field techniques and Monte Carlo simulations. The
anisotropy is encoded in the gauge couplings as well as in the Higgs couplings.
In addition to the usual bulk phases (confining, Coulomb and Higgs) we find
four-dimensional ``layered'' phases (3-branes) at weak gauge coupling, where
the layers may be in either the Coulomb or the Higgs phase, while the
transverse directions are confining.Comment: LaTeX (amssymb.sty and psfig) 21 pages, 17 figure
Discovering New Physics in the Decays of Black Holes
If the scale of quantum gravity is near a TeV, the LHC will be producing one
black hole (BH) about every second, thus qualifying as a BH factory. With the
Hawking temperature of a few hundred GeV, these rapidly evaporating BHs may
produce new, undiscovered particles with masses ~100 GeV. The probability of
producing a heavy particle in the decay depends on its mass only weakly, in
contrast with the exponentially suppressed direct production. Furthemore, BH
decays with at least one prompt charged lepton or photon correspond to the
final states with low background. Using the Higgs boson as an example, we show
that it may be found at the LHC on the first day of its operation, even with
incomplete detectors.Comment: 4 pages, 3 figure
\Delta S=2 and \Delta C=2 bag parameters in the SM and beyond from Nf=2+1+1 twisted-mass LQCD
We present unquenched lattice QCD results for the matrix elements of
four-fermion operators relevant to the description of the neutral K and D
mixing in the Standard Model and its extensions. We have employed simulations
with Nf = 2 + 1 + 1 dynamical sea quarks at three values of the lattice
spacings in the interval 0.06 - 0.09 fm and pseudoscalar meson masses in the
range 210 - 450 MeV. Our results are extrapolated to the continuum limit and to
the physical pion mass. Renormalization constants have been determined
non-perturbatively in the RI-MOM scheme. In particular, for the Kaon
bag-parameter, which is relevant for the \overline{K}^0-K^0 mixing in the
Standard Model, we obtain B_K^{RGI} = 0.717(24).Comment: Added comments to error budget discussion; fig.19 corrected. Version
to appear in PR
Flavour symmetry restoration and kaon weak matrix elements in quenched twisted mass QCD
We simulate two variants of quenched twisted mass QCD (tmQCD), with
degenerate Wilson quarks of masses equal to or heavier than half the strange
quark mass. We use Ward identities in order to measure the twist angles of the
theory and thus check the quality of the tuning of mass parameters to a physics
condition which stays constant as the lattice spacing is varied. Flavour
symmetry breaking in tmQCD is studied in a framework of two fully twisted and
two standard Wilson quark flavours, tuned to be degenerate in the continuum.
Comparing pseudoscalar masses, obtained from connected quark diagrams made of
tmQCD and/or standard Wilson quark propagators, we confirm that flavour
symmetry breaking effects, which are at most 5%, decrease as we approach the
continuum limit. We also compute the pseudoscalar decay constant in the
continuum limit, with reduced systematics. As a consequence of improved tuning
of the mass parameters at , we reanalyse our previous
results. Our main phenomenological findings are and .Comment: 41 pages, figures included, one reference added. Final version as
accepted for publication on Nucl.Phys.
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