36 research outputs found
Flavour symmetries in the SMEFT
We analyse how and flavour symmetries act on the Standard
Model Effective Field Theory, providing an organising principle to classify the
large number of dimension-six operators involving fermion fields. A detailed
counting of such operators, at different order in the breaking terms of both
these symmetries, is presented. A brief discussion about possible deviations
from these two reference cases, and a simple example of the usefulness of this
classification scheme for high- analyses at the LHC, are also presented.Comment: 31 pages, 13 Table
Lepton Flavor Violation and Dilepton Tails at the LHC
Starting from a general effective Lagrangian for lepton flavor violation
(LFV) in quark-lepton transitions, we derive constraints on the effective
coefficients from the high-mass tails of the dilepton processes (with ). The current (projected) limits derived in this paper
from LHC data with () can be applied
to generic new physics scenarios, including the ones with scalar, vector and
tensor effective operators. For purely left-handed operators, we explicitly
compare these LHC constraints with the ones derived from flavor-physics
observables, illustrating the complementarity of these different probes. While
flavor physics is typically more constraining for quark-flavor violating
operators, we find that LHC provides the most stringent limits on several
flavor-conserving ones. Furthermore, we show that dilepton tails offer the best
probes for charm-quark transitions at current luminosities and that they
provide competitive limits for tauonic transitions at the
high-luminosity LHC phase. As a by-product, we also provide general numerical
expressions for several low-energy LFV processes, such as the semi-leptonic
decays , and .Comment: 14 pages, 2 figures, 5 tables, published versio
Drell-Yan Tails Beyond the Standard Model
We investigate the high- tails of the and Drell-Yan processes as probes of New Physics in semileptonic interactions
with an arbitrary flavor structure. For this purpose, we provide a general
decomposition of the scattering amplitudes in terms of form-factors
that we match to specific scenarios, such as the Standard Model Effective Field
Theory (SMEFT), including all relevant operators up to dimension-, as well
as ultraviolet scenarios giving rise to tree-level exchange of new bosonic
mediators with masses at the TeV scale. By using the latest LHC run-II data in
the monolepton (, , ) and dilepton (, ,
, , , ) production channels, we derive
constraints on the SMEFT Wilson coefficients for semileptonic four-fermion and
dipole operators with the most general flavor structure, as well as on all
possible leptoquark models. For the SMEFT, we discuss the range of validity of
the EFT description, the relevance of and
truncations, the impact of operators and the
effects of different quark-flavor alignments. Finally, as a highlight, we
extract for several New Physics scenarios the combined limits from high-
processes, electroweak pole measurements and low-energy flavor data for the
transition, showing the complementarity between these different
observables. Our results are compiled in {\tt HighPT}, a package in {\tt
Mathematica} which provides a simple way for users to extract the Drell-Yan
tails likelihoods for semileptonic effective operators and for leptoquark
models.Comment: 61 pages, 19 figure
HighPT: A Tool for high- Drell-Yan Tails Beyond the Standard Model
HighPT is a Mathematica package for the analysis of high-energy data of
semileptonic transitions at hadron colliders. It allows to compute high-
tail observables for semileptonic processes, i.e. Drell-Yan cross sections, for
dilepton and monolepton final states at the LHC. These observables can be
calculated at tree level within the Standard Model Effective Field Theory,
including the relevant operators up to dimension eight to ensure a consistent
description of the cross section including terms of
in the cutoff scale . For New Physics models with new mediators that
can be resolved at LHC energies, HighPT can also account for the full
propagation effects of these new bosonic states at tree level. Using the
available data from the high- tails in the relevant LHC run-II searches by
the ATLAS and CMS collaborations, HighPT can also construct the corresponding
likelihoods for all possible flavors of the leptonic final states. As an
illustration, we derive and compare constraints on Wilson coefficients at
different orders in the Effective Field Theory expansion, and we investigate
lepton flavor violation for the leptoquark model. The HighPT code is
publicly available at https://github.com/HighPT/HighPT.Comment: 34 page
Reading the footprints of the B-meson flavor anomalies
Motivated by the recent LHCb announcement of a violation of
lepton-flavor universality in the ratio , we present an updated, comprehensive
analysis of the flavor anomalies seen in both neutral-current () and charged-current () decays of mesons.
Our study starts from a model-independent effective field-theory approach and
then considers both a simplified model and a UV-complete extension of the
Standard Model featuring a vector leptoquark as the main mediator of the
anomalies. We show that the new LHCb data corroborate the emerging pattern of a
new, predominantly left-handed, semileptonic current-current interaction with a
flavor structure respecting a (minimally) broken flavor symmetry. New
aspects of our analysis include a combined analysis of the semileptonic
operators involving tau leptons, including in particular the important
constraint from -- mixing, a systematic study of the effects of
right-handed leptoquark couplings and of deviations from minimal
flavor-symmetry breaking, a detailed analysis of various rare -decay modes
which would provide smoking-gun signatures of this non-standard framework (LFV
decays, di-tau modes, and ), and finally an updated
analysis of collider bounds on the leptoquark mass and couplings.Comment: 41 pages, 14 figures, 4 table