626 research outputs found
On the Hadronic Contribution to Light-by-light Scattering in
We comment on the theoretical uncertainties involved in estimating the
hadronic effects on the light-by-light scattering contribution to the anomalous
magnetic moment of the muon, especially based on the analysis and results of T.
Kinoshita, B. Ni\v zi\'c, and Y. Okamoto, Phys.\ Rev.\ D31, 2108 (1985). From
the point of view of an effective field theory and chiral perturbation theory,
we suggest that the charged pion contribution may be better determined than has
been appreciated. However, the neutral pion contribution needs greater
theoretical insight before its magnitude can be reliably estimated.Comment: 9 pages, no figures, U. Michigan UM-TH-93-18. (Input phyzzm to
compile.) Revised version has minor changes in text. To be published in Phys.
Rev. D, Comments sectio
Treatment of sleep apnea in chronic heart failure patients with auto-servo ventilation improves sleep fragmentation: a randomized controlled trial
Background: Impaired sleep efficiency is independently associated with worse prognosis in patients with chronic heart failure (CHF). Therefore, a test was conducted on whether auto-servo ventilation (ASV, biphasic positive airway pressure [BiPAP]-ASV, Philips Respironics) reduces sleep fragmentation and improves sleep efficiency in CHF patients with central sleep apnea (CSA) or obstructive sleep apnea (OSA). Methods: In this multicenter, randomized, parallel group trial, a study was conducted on 63 CHF patients (age 64 +/- 10 years; left ventricular ejection fraction 29 +/- 7%) with CSA or OSA (apnea-hypopnea Index, AHI 47 +/- 18/h; 46% CSA) referred to sleep laboratories of the four participating centers. Participants were randomized to either ASV (n = 32) or optimal medical treatment alone (control, n = 31). Results: Polysomnography (PSG) and actigraphy at home (home) with centralized blinded scoring were obtained at baseline and 12 weeks. ASV significantly reduced sleep fragmentation (total arousal indexpsc: -16.4 +/- 20.6 vs.-0.6 13.2/h, p = 0.001; sleep fragmentation index(home):-7.6 +/- 15.6 versus 4.3 +/- 13.9/h, p = 0.003, respectively) and significantly increased sleep efficiency assessed by actigraphy (SEhome) compared to controls (2.3 +/- 10.1 vs.-2.1 +/- 6.9%, p = 0.002). Effects of ASV on sleep fragmentation and efficiency were similar in patients suffering from OSA and CSA. Conclusions: At home, ASV treatment modestly improves sleep fragmentation as well as sleep efficiency in CHF patients having either CSA or OSA. (C) 2015 Elsevier B.V. All rights reserved
CP violation in gauge theories
We define the CP transformation properties of scalars, fermions and vectors
in a gauge theory and show that only three types of interactions can lead to CP
violation: scalar interactions, fermion-scalar interactions and
associated with the strong CP problem and which involve only the gauge fields.
For technicolor theories this implies the absence of CP violation within
perturbation theory.Comment: 5 pages, 1 figure, revtex and epsf require
Dimension-Six Terms in the Standard Model Lagrangian
When the Standard Model is considered as an effective low-energy theory,
higher dimensional interaction terms appear in the Lagrangian. Dimension-six
terms have been enumerated in the classical article by Buchmueller and Wyler
[3]. Although redundance of some of those operators has been already noted in
the literature, no updated complete list has been published to date. Here we
perform their classification once again from the outset. Assuming baryon number
conservation, we find 15 + 19 + 25 = 59 independent operators (barring flavour
structure and Hermitian conjugations), as compared to 16 + 35 + 29 = 80 in
Ref.[3]. The three summed numbers refer to operators containing 0, 2 and 4
fermion fields. If the assumption of baryon number conservation is relaxed, 4
new operators arise in the four-fermion sector.Comment: 16 pages, no figures, v3: Redundant B-violating operator remove
Four-Fermi Effective Operators in Top-Quark Production and Decay
Effects of four-Fermi-type new interactions are studied in top-quark pair
production and their subsequent decays at future e^+e^- colliders.
Secondary-lepton-energy distributions are calculated for arbitrary longitudinal
beam polarizations. An optimal-observables procedure is applied for the
determination of new parameters.Comment: Polarized e^- plus unpolarized e^+ collisions were include
Muon Anomalous Magnetic Moment and Lepton Flavor Violation
A non-universal interaction, which involves only the third family leptons
induces lepton flavor violating couplings and contributes to the anomalous
magnetic moment of muon. In this paper, we study the effects of non-universal
interaction on muon (g-2) and rare decay by using an
effective lagrangian technique, and a phenomenological model where
couples only to the third family lepton. We find that the deviation
from the theory can be explained and the induced rate
could be very close to the current experimental limit. In the model,
has to be lighter than 2.6 TeV.Comment: references added, the version to appear in PR
A Perturbative Calculation of the Electromagnetic Form Factors of the Deuteron
Making use of the effective field theory expansion recently developed by the
authors, we compute the electromagnetic form factors of the deuteron
analytically to next-to-leading order (NLO). The computation is rather simple,
and involves calculating several Feynman diagrams, using dimensional
regularization. The results agree well with data and indicate that the
expansion is converging. They do not suffer from any ambiguities arising from
off-shell versus on-shell amplitudes.Comment: 22 pages, 8 figures. Discussion of effective range theory added,
typos correcte
Sensitivity to anomalous quartic gauge couplings in photon-photon interactions at the LHC
The exclusive two-photon production at the LHC of pairs of W and Z bosons
provides a novel and unique test-ground for the electroweak gauge boson sector.
In particular it offers, thanks to high gamma-gamma center-of-mass energies,
large and direct sensitivity to the anomalous quartic gauge couplings otherwise
very difficult to investigate at the LHC. An initial analysis has been
performed assuming leptonic decays and generic acceptance cuts. Simulation of a
simple counting experiment has shown for the integrated luminosity of 10 fb-1
at least four thousand times larger sensitivity to the genuine quartic
couplings, a_0^W, a_0^Z, a_C^W and a_C^Z, than those obtained at LEP. The
impact of the unitarity constraints on the estimated limits has been studied
using the dipole form-factors. Finally, differential distributions of the decay
leptons have been provided to illustrate the potential for further improvements
of the sensitivities.Comment: 8 pages and 11 figures, Contribution to the CERN workshop on "High
energy photon collisions at the LHC", 22-25 April 200
Effective Theory of a Dynamically Broken Electroweak Standard Model at NLO
We consider the Standard Model as an effective theory at the weak scale
of a generic new strong interaction that dynamically breaks electroweak
symmetry at the energy scale (few) TeV. Assuming only the
minimal field content with the Standard Model fermions and gauge bosons, but
without a light Higgs particle, we construct the complete Lagrangian through
next-to-leading order, that is, including terms of order . The
systematics behind this expansion is clarified. Although similar to chiral
perturbation theory, it is not governed by the dimension of operators alone,
but depends in an essential way on the loop expansion. Power-counting formulas
are derived that indicate the classes of operators required at the
next-to-leading order. The complete set of operators at leading and
next-to-leading order is then listed, based on the restrictions implied by the
Standard-Model gauge symmetries. We recover the well-known operators discussed
in the literature in connection with the electroweak chiral Lagrangian and in
similar contexts, but we collect a complete and systematic list of all terms
through order . This includes some operators not discussed in
explicit terms before. We also show that a few of the previously considered
operators can be eliminated via the equations of motion. As another important
result we confirm the known list of dimension-6 operators in the Standard Model
with an elementary Higgs doublet, essentially as a special case of our
scenario.Comment: 35 pages, 1 figure; references adde
Testing new physics/couplings at the NLC (Talk prsented in The 5th Topical Seminar on ``The irresistible rise of the Standard Model'', San Miniato al Todesco, Italy, April 21-25 1997)
I present a brief overview of the advantages of using a consistent effective
Lagrangian approach in parameterizing virtual new physics effects. I then apply
the formalism to certain top-quark processes.Comment: 7 pages, 5 figures. Requires epsf.st
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