284 research outputs found
Stringy explanation of anomalies
We show that the recent anomalies in transitions
observed by the LHCb collaboration can be accommodated within string motivated
models with a low mass gauge boson. Such gauge boson
can be obtained in compactifications with a low string scale. We consider a
class of intersecting D-brane models, in which different families of quarks and
leptons are simultaneously realized at different D-brane intersections. The
explanation of anomalies via a stringy
sets important restrictions on these viable D-brane constructions.Comment: 18 pages, 13 figure
Effective Aligned 2HDM with a DFSZ-like invisible axion
We discuss the possibility of having a non-minimal scalar sector at the weak
scale within the framework of invisible axion models. To frame our discussion
we consider an extension of the Dine-Fischler-Srednicki-Zhitnitsky invisible
axion model with two additional Higgs doublets blind under the Peccei-Quinn
symmetry. Due to mixing effects among the scalar fields, it is possible to
obtain a rich scalar sector at the weak scale in certain decoupling limits of
the theory. In particular, this framework provides an ultraviolet completion of
the so-called aligned two-Higgs-doublet model and solves the strong CP problem.
The axion properties and the smallness of active neutrino masses are also
discussed.Comment: 8 pages, 1 figure. Discussion improved, references added. Matching
the journal versio
Yukawa enhancement of -mediated New Physics in and Processes
We discuss Yukawa-enhanced contributions from -mediated new physics to
down-type quark processes in the framework of the standard model
gauge-invariant effective theory (SMEFT). Besides the renormalization group
(RG) mixing of the -mediating operators into
operators, we include at the electroweak scale one-loop (NLO) matching
corrections consistently, necessary for the removal of the matching scale
dependence. We point out that the right-handed -mediated interactions
generate through Yukawa RG mixing left-right operators, which are
further enhanced through QCD RG effects and chirally enhanced hadronic matrix
elements. We investigate the impact of these new effects on the known
correlations between and transitions in the SMEFT
framework and point out qualitative differences to previous parameterizations
of -mediated new physics that arise for the left-handed case. We illustrate
how specific models fit into our model-independent framework by using four
models with vector-like quarks. We carry out model-independent analyses of
scenarios with purely left-handed and purely right-handed new-physics
couplings for each of the three sectors , and .
Specifically we discuss the correlations between ,
, and
in the Kaon sector, and ,
and in the sector and
in the sector.Comment: 40 pages, 11 figures; v2: 2nd plot in figure 2 and references added,
comparison with v2 of 1612.08839, conclusion unchanged; v3: improvements on
text and presentation, matches published versio
Gauge-invariant implications of the LHCb measurements on Lepton-Flavour Non-Universality
We study the implications of the recent measurements of and
by the LHCb collaboration. We do that by adopting a model-independent approach
based on the Standard Model Effective Field Theory (SMEFT), in which the
dominant new physics effects are encoded in the coefficients of dimension-six
operators respecting the full Standard Model (SM) gauge symmetry. After
providing simplified expressions for and , we determine the
implications of the recent LHCb results for these observables on the
coefficients of the SMEFT operators at low and high energies. We also take into
account all data, which combined lead to effective New
Physics (NP) scenarios with SM pulls in excess of 5~. Thus the
operators discussed in this paper would be the first dimension-six terms in the
SM Lagrangian to be detected experimentally. Indirect constraints on these
operators are also discussed. The results of this paper transcend the
singularity of the present situation, and set a standard for future analyses in
transitions when the NP is assumed to lie above the electroweak scale.Comment: 10 pages, 2 figures, 3 tables. v2: references added, typos corrected,
improved discussion in Sec. V, corrected coefficient of C7 in formula for
RKstar in the low-bin, new figure with global fit in terms of SMEFT
coefficients. Conclusions unchanged. v3: minor addition, shorter version to
be published in PR
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