92 research outputs found
Perfect Scalars on the Lattice
We perform renormalization group transformations to construct optimally local
perfect lattice actions for free scalar fields of any mass. Their couplings
decay exponentially. The spectrum is identical to the continuum spectrum, while
thermodynamic quantities have tiny lattice artifacts. To make such actions
applicable in simulations, we truncate the couplings to a unit hypercube and
observe that spectrum and thermodynamics are still drastically improved
compared to the standard lattice action. We show how preconditioning techniques
can be applied successfully to this type of action. We also consider a number
of variants of the perfect lattice action, such as the use of an anisotropic or
triangular lattice, and modifications of the renormalization group
transformations motivated by wavelets. Along the way we illuminate the
consistent treatment of gauge fields, and we find a new fermionic fixed point
action with attractive properties.Comment: 26 pages, 11 figure
Unravelling quantum carpets: a travelling wave approach
Quantum carpets are generic spacetime patterns formed in the probability
distributions P(x,t) of one-dimensional quantum particles, first discovered in
1995. For the case of an infinite square well potential, these patterns are
shown to have a detailed quantitative explanation in terms of a travelling-wave
decomposition of P(x,t). Each wave directly yields the time-averaged structure
of P(x,t) along the (quantised)spacetime direction in which the wave
propagates. The decomposition leads to new predictions of locations, widths
depths and shapes of carpet structures, and results are also applicable to
light diffracted by a periodic grating and to the quantum rotator. A simple
connection between the waves and the Wigner function of the initial state of
the particle is demonstrated, and some results for more general potentials are
given.Comment: Latex, 26 pages + 6 figures, submitted to J. Phys. A (connections
with prior literature clarified
Constraints on Two-Higgs Doublet Models at Large tan{beta} from W and Z decays
We study constraints on type-II two Higgs doublet models at large tan{beta}
from LEP/SLD Z-pole data and from lepton universality violation in W decay. We
perform a global fit and find that, in the context of Z decay, the LEP/SLD
experimental values for lepton universality violation, R_b, and A_b all
somewhat disfavor the model. Contributions from the neutral Higgs sector can be
used to constrain the scalar-pseudoscalar Higgs mass splittings. Contributions
from the charged Higgs sector allow us to constrain the charged Higgs mass. For
tan{beta}=100 we obtain the 1 sigma classical (Bayesian) bounds of m_{H+} > 670
GeV (370 GeV) and 1 > m_{h0}/m_{A0} > 0.68 (0.64). The 2 sigma bounds are weak.
Currently, the Tevatron experimental limits on lepton universality violation in
W decay provide no significant constraint on the Higgs sector.Comment: 26 pages, 9 postscript figures, REVTe
Interpretations of the NuTeV
We summarize theoretical explanations of the three discrepancy
between measured by NuTeV and predicted by the Standard Model
global fit. Possible new physics explanations ({\it e.g.} an unmized ) are
not compelling. The discrepancy would be reduced by a positive momentum
asymmetry in the strange sea; present experimental estimates of are
unreliable or incomplete. Upgrading the NuTeV analysis to NLO would alleviate
concerns that the discrepancy is a QCD effect.Comment: (proceedings for the NuFact'02 Workshop); reference and footnote
added, following the NuTeV proceeding
Coherent states of P{\"o}schl-Teller potential and their revival dynamics
A recently developed algebraic approach for constructing coherent states for
solvable potentials is used to obtain the displacement operator coherent state
of the P\"{o}schl-Teller potential. We establish the connection between this
and the annihilation operator coherent state and compare their properties. We
study the details of the revival structure arising from different time scales
underlying the quadratic energy spectrum of this system.Comment: 13 pages, 6 figure
Recent Developments in Precision Electroweak Physics
Developments in precision electroweak physics in the two years since the
symposium are briefly summarized.Comment: Update on recent developments, prepared for the publication of the
Proceedings of Alberto Sirlin Symposium, New York University, October 2000.
10 pages, 1 figur
Higgs-Boson Mass Limits and Precise Measurements beyond the Standard Model
The triviality and vacuum stability bounds on the Higgs-boson mass (\mh)
were revisited in presence of weakly-coupled new interactions parameterized in
a model-independent way by effective operators of dimension 6. The constraints
from precision tests of the Standard Model were taken into account. It was
shown that for the scale of new physics in the region \Lambda \simeq 2 \div 50
\tev the Standard Model triviality upper bound remains unmodified whereas it
is natural to expect that the lower bound derived from the requirement of
vacuum stability is substantially modified depending on the scale \La and
strength of coefficients of effective operators. A natural generalization of
the standard triviality condition leads also to a substantial reduction of the
allowed region in the (\Lambda,\mh) space.Comment: 18 pages 3 eps figures. The discussion in the appendix was modified
slightly and some typographical errors were correcte
Critical dimensions of the diffusion equation
We study the evolution of a random initial field under pure diffusion in
various space dimensions. From numerical calculations we find that the
persistence properties of the system show sharp transitions at critical
dimensions d1 ~ 26 and d2 ~ 46. We also give refined measurements of the
persistence exponents for low dimensions.Comment: 4 pages, 5 figure
Bounds on the Higgs-Boson Mass in the Presence of Non-Standard Interactions
The triviality and vacuum stability bounds on the Higgs-boson mass are
revisited in the presence of new interactions parameterized in a
model-independent way by an effective lagrangian. When the scale of new physics
is below 50 TeV the triviality bound is unchanged but the stability lower bound
is increased by 40-60 GeV. Should the Higgs-boson mass be close to its current
lower experimental limit, this leads to the possibility of new physics at the
scale of a few TeV, even for modest values of the effective lagrangian
parameters.Comment: 5 pages, 2 figures, RevTex, submitted to PR
Coherent state of a nonlinear oscillator and its revival dynamics
The coherent state of a nonlinear oscillator having a nonlinear spectrum is
constructed using Gazeau Klauder formalism. The weighting distribution and the
Mandel parameter are studied. Details of the revival structure arising from
different time scales underlying the quadratic energy spectrum are investigated
by the phase analysis of the autocorrelation function
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