357 research outputs found
Sum rules for asymptotic form factors in scattering
At very large energies and in gauge theories, the
trilinear gauge boson vertices relevant for scattering are
related in a simple way to the gauge boson self-energies. We derive these
relations, both from the requirement of perturbative unitarity and from the
Ward Identities of the theory. Our discussion shows that, in general, it is
never possible to neglect vector boson self-energies when computing the form
factors which parametrize the helicity amplitudes. The
exclusion of the self-energy contributions would lead to estimates of the
effects wrong by orders of magnitudes. We propose a simple way of including the
self-energy contributions in an appropriate definition of the form factors.Comment: 16 pages, latex file, 2 eps figures, need epsfig.st
Revisiting the production of ALPs at B-factories
In this paper, the production of Axion-Like Particles (ALPs) at B-factories via the process e+e− → γa is revisited. To this purpose, the relevant cross-section is computed via an effective Lagrangian with simultaneous ALP couplings to b-quarks and photons. The interplay between resonant and non-resonant contributions is shown to be relevant for experiments operating at s=mϒ(nS), with n = 1, 2, 3, while the non-resonant one dominates at ϒ(4S). These effects imply that the experimental searches performed at different quarkonia resonances are sensitive to complementary combinations of ALP couplings. To illustrate these results, constraints from existing BaBar and Belle data on ALPs decaying into invisible final states are derived, and the prospects for the Belle-II experiment are discussedThe authors acknowledge F. Anulli, D. Becirevic, S. Fajfer, A. Guerrera, C. Hearty,
S.J.D. King, T. Ferben, S. Lacaprara, M. Margoni, F. Mescia, M. Passera and P. Paradisi for very useful exchanges. This project has received support by the European Union’s
Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant
agreement N◦ 674896 (ITN Elusives) and 690575 (RISE InvisiblePlus) and by the exchange
of researchers project “The flavor of the invisible universe” funded by the Italian Ministry
of Foreign Affairs and International Cooperation (MAECI). L.M. acknowledges partial
financial support by the Spanish MINECO through the “Ram´on y Cajal” programme
(RYC-2015-17173), by the Spanish “Agencia Estatal de Investigaci´on” (AEI) and the EU
“Fondo Europeo de Desarrollo Regional” (FEDER) through the project FPA2016-78645-P,
and through the Centro de excelencia Severo Ochoa Program under grant SEV-2016-0597.
L.M. thanks the Physics and Astronomy Department ‘G.Galilei’ of the Universit`a degli
Studi di Padova for hospitality during the development of this projec
Higgs portal dark matter and neutrino mass and mixing with a doubly charged scalar
We consider an extension of the Standard Model involving two new scalar
particles around the TeV scale: a singlet neutral scalar , to be
eventually identified as the Dark Matter candidate, plus a doubly charged
singlet scalar, , that can be the source for the
non-vanishing neutrino masses and mixings. Assuming an unbroken symmetry
in the scalar sector, under which only the additional neutral scalar is
odd, we write the most general (renormalizable) scalar potential. The model may
be regarded as a possible extension of the conventional Higgs portal Dark
Matter scenario which also accounts for neutrino mass and mixing. This
framework cannot completely explain the observed positron excess. However a
softening of the discrepancy observed in conventional Higgs portal framework
can be obtained, especially when the scale of new physics responsible for
generating neutrino masses and lepton number violating processes is around 2
TeV.Comment: 16 pages, 4 figure
Fermion Virtual Effects in Cross Section
We analyse the contribution of new heavy virtual fermions to the cross section. We find that there exists a relevant
interplay between trilinear and bilinear oblique corrections. The result
strongly depends on the chiral or vector--like nature of the new fermions. As
for the chiral case we consider sequential fermions: one obtains substantial
deviation from the Standard model prediction, making the effect possibly
detectable at or GeV linear colliders. As an example for
the vector--like case we take a SUSY extension with heavy charginos and
neutralinos: due to cancellation, the final effect turns out to be negligible.Comment: uuencoded, gz-compressed, tar-ed file. 8 pages, 4 EPS figures, uses
EPSFIG.ST
One-loop effective potential in M4 x T2 with and without 't Hooft flux
We review the basic notions of compactification in the presence of a
background flux. In extra-dimentional models with more than five dimensions,
Scherk and Schwarz boundary conditions have to satisfy 't Hooft consistency
conditions. Different vacuum configurations can be obtained, depending whether
trivial or non-trivial 't Hooft flux is considered. The presence of the
"magnetic" background flux provide, in addition, a mechanism for producing
four-dimensional chiral fermions. Particularizing to the six-dimensional case,
we calculate the one-loop effective potential for a U(N) gauge theory on M4 x
T2. We firstly review the well known results of the trivial 't Hooft flux case,
where one-loop contributions produce the usual Hosotani dynamical symmetry
breaking. Finally we applied our result for describing, for the first time, the
one-loop contributions in the non-trivial 't Hooft flux case
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