139 research outputs found
What is the scale of new physics behind the B-flavour anomalies?
Motivated by the recent hints of lepton flavour non-universality in B-meson semi-leptonic decays, we study the constraints of perturbative unitarity on the new physics interpretation of the anomalies in b→cℓν¯b→cℓν¯ and b→sℓℓ¯b→sℓℓ¯ transitions. Within an effective field theory approach we find that 2→22→2 fermion scattering amplitudes saturate the unitarity bound below 9 and 80 TeV, respectively for b→cℓν¯b→cℓν¯ and b→sℓℓ¯b→sℓℓ¯ transitions. Stronger bounds, up to few TeV, are obtained when the leading effective operators are oriented in the direction of the third generation, as suggested by flavour models. We finally address unitarity constraints on simplified models explaining the anomalies and show that the new physics interpretation is ruled out in a class of perturbative realizations
Accidental matter at the LHC
We classify weak-scale extensions of the Standard Model which automatically
preserve its accidental and approximate symmetry structure at the
renormalizable level and which are hence invisible to low-energy indirect
probes. By requiring the consistency of the effective field theory up to scales
of 10^15 GeV and after applying cosmological constraints, we arrive at a finite
set of possibilities that we analyze in detail. One of the most striking
signatures of this framework is the presence of new charged and/or colored
states which can be efficiently produced in high-energy particle colliders and
which are stable on the scale of detectors.Comment: 55 pages, 13 figure
What is the scale of new physics behind the muon ?
We study the constraints imposed by perturbative unitarity on the new physics
interpretation of the muon anomaly. Within a Standard Model Effective
Field Theory (SMEFT) approach, we find that scattering amplitudes sourced by
effective operators saturate perturbative unitarity at about 1 PeV. This
corresponds to the highest energy scale that needs to be probed in order to
resolve the new physics origin of the muon anomaly. On the other hand,
simplified models (e.g.~scalar-fermion Yukawa theories) in which renormalizable
couplings are pushed to the boundary of perturbativity still imply new on-shell
states below 200 TeV. We finally suggest that the highest new physics scale
responsible for the anomalous effect can be reached in non-renormalizable
models at the PeV scale.Comment: 16 pages, 4 figure
Stellar evolution confronts axion models
Axion production from astrophysical bodies is a topic in continuous development, because of theoretical progress in the estimate of stellar emission rates and, especially, because of improved stellar observations. We carry out a comprehensive analysis of the most informative astrophysics data, revisiting the bounds on axion couplings to photons, nucleons and electrons, and reassessing the significance of various hints of anomalous stellar energy losses. We confront the performance of various theoretical constructions in accounting for these hints, while complying with the observational limits on axion couplings. We identify the most favorable models, and the regions in the mass/couplings parameter space which are preferred by the global fit. Finally, we scrutinize the discovery potential for such models at upcoming helioscopes, namely IAXO and its scaled versions
Solar axions cannot explain the XENON1T excess
We argue that the interpretation in terms of solar axions of the recent
XENON1T excess is not tenable when confronted with astrophysical observations
of stellar evolution. We discuss the reasons why the emission of a flux of
solar axions sufficiently intense to explain the anomalous data would radically
alter the distribution of certain type of stars in the color-magnitude diagram
in first place, and would also clash with a certain number of other
astrophysical observables. Quantitatively, the significance of the discrepancy
ranges from for the rate of period change of pulsating White
Dwarfs, and exceedes for the -parameter and for .Comment: 6 pages, 2 figures, 1 table. Version accepted for publication on PR
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