128 research outputs found
Towards a determination of the tau lepton dipole moments
The tau anomalous magnetic moment (a_tau) and electric dipole moment (d_tau)
have not yet been observed. The present bounds on their values are of order
10^-2 and 10^-17 e*cm, respectively. We propose to measure a_tau with a
precision of O(10^-3) or better and improve the existing limits on d_tau using
precise tau- -> l- nu_tau \bar{nu}_l gamma (l=e or mu) data from
high-luminosity B factories. A detailed feasibility study of this method is
underway.Comment: 4 pages, presented at the 12th International Workshop on Tau Lepton
Physics, Nagoya, Japan, 17-21 September 201
Master integrals for the NNLO virtual corrections to scattering in QED: the planar graphs
We evaluate the master integrals for the two-loop, planar box-diagrams
contributing to the elastic scattering of muons and electrons at
next-to-next-to leading-order in QED. We adopt the method of differential
equations and the Magnus exponential series to determine a canonical set of
integrals, finally expressed as a Taylor series around four space-time
dimensions, with coefficients written as combination of generalised
polylogarithms. The electron is treated as massless, while we retain full
dependence on the muon mass. The considered integrals are also relevant for
crossing-related processes, such as di-muon production at -colliders,
as well as for the QCD corrections to -pair production at hadron
colliders.Comment: published version, 39 pages, 7 figures, 3 ancillary file
Remarks on higher-order hadronic corrections to the muon g-2
Recently, it was shown that insertions of hadronic vacuum polarization at
O(alpha^4) generate non-negligible effects in the calculation of the anomalous
magnetic moment of the muon. This result raises the question if other hadronic
diagrams at this order might become relevant for the next round of g-2
measurements as well. In this note we show that a potentially enhanced such
contribution, hadronic light-by-light scattering in combination with electron
vacuum polarization, is already sufficiently suppressed.Comment: 2 pages, 1 figure; journal versio
Limiting two-Higgs-doublet models
We update the constraints on two-Higgs-doublet models (2HDMs) focusing on the
parameter space relevant to explain the present muon anomaly, , in four different types of models, type I, II, "lepton specific" (or
X) and "flipped" (or Y). We show that the strong constraints provided by the
electroweak precision data on the mass of the pseudoscalar Higgs, whose
contribution may account for , are evaded in regions where the
charged scalar is degenerate with the heavy neutral one and the mixing angles
and satisfy the Standard Model limit . We combine theoretical constraints from vacuum stability and
perturbativity with direct and indirect bounds arising from collider and
~physics. Possible future constraints from the electron are also
considered. If the 126 GeV resonance discovered at the LHC is interpreted as
the light CP-even Higgs boson of the 2HDM, we find that only models of type X
can satisfy all the considered theoretical and experimental constraints.Comment: 18 pages, 3 figure
Comment on: Beverly et al. Do older adults aged 60-75 years benefit from diabetes behavioral interventions? Diabetes Care
New physics behind the new muon -2 puzzle?
The recent measurement of the muon -2 at Fermilab confirms the previous
Brookhaven result. The leading hadronic vacuum polarization (HVP) contribution
to the muon -2 represents a crucial ingredient to establish if the Standard
Model prediction differs from the experimental value. A recent lattice QCD
result by the BMW collaboration shows a tension with the low-energy data which are currently used to determine the HVP
contribution. We refer to this tension as the new muon -2 puzzle. In this
Letter we consider the possibility that new physics contributes to the cross-section. This scenario could, in principle, solve the
new muon -2 puzzle. However, we show that this solution is excluded by a
number of experimental constraints.Comment: 6 pages, 4 figures. Version to appear in Physics Letters
Contributions of axionlike particles to lepton dipole moments
Contributions of a spin 0 axion-like particle (ALP) to lepton dipole moments,
g-2 and EDMs, are examined. Barr-Zee and light-by-light loop effects from a
light pseudoscalar ALP are found to be capable of resolving the long-standing
muon g-2 discrepancy at the expense of relatively large ALP-gammagamma
couplings. The compatibility of such large couplings with direct experimental
constraints and perturbative unitarity bounds is discussed. Future tests of
such a scenario are described. For CP violating ALP couplings, the electron EDM
is found to probe much smaller, theoretically more easily accommodated ALP
interactions. Future planned improvement in electron EDM searches is advocated
as a way to not only significantly constrain ALP parameters but also, to
potentially unveil a new source of CP violation which could have far reaching
ramifications.Comment: 5 pages, 4 figures. V2: Title shortened and several references added.
More emphasis on contributions of Barr-Zee diagrams, along with an extended
discussion of the allowed parameter space of ALP solutions to the muon g-2
discrepancy incorporated. V3: Minor text improvments. Published versio
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