3,708 research outputs found
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
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
Phenomenology of an model with lepton-flavour non-universality
We investigate a gauge extension of the Standard Model in light of the
observed hints of lepton universality violation in and decays at BaBar, Belle and LHCb. The model consists of an
extended gauge group which breaks spontaneously around the TeV scale to the
electroweak gauge group. Fermion mixing effects with vector-like fermions give
rise to potentially large new physics contributions in flavour transitions
mediated by and bosons. This model can ease tensions
in -physics data while satisfying stringent bounds from flavour physics, tau
decays, and electroweak precision data. Possible ways to test the proposed new
physics scenario with upcoming experimental measurements are discussed. Among
other predictions, the lepton flavour violating ratios , with , are found to be reduced with respect to the Standard Model expectation
.Comment: 46 pages, 11 figures. v2: version published in JHE
Non-abelian gauge extensions for B-decay anomalies
We study the generic features of minimal gauge extensions of the Standard
Model in view of recent hints of lepton-flavor non-universality in
semi-leptonic and decays. We
classify the possible models according to the symmetry-breaking pattern and the
source of flavor non-universality. We find that in viable models the
factor is embedded non-trivially in the extended gauge
group, and that gauge couplings should be universal, hinting to the presence of
new degrees of freedom sourcing non-universality. Finally, we provide an
explicit model that can explain the -decay anomalies in a coherent way and
confront it with the relevant phenomenological constraints.Comment: 8 pages, 2 figures; discussion improved, a figure and references
added; conclusions unchange
Structural Design of a Crashworthy Energy Absorbing Passenger Seat For a Large Transport Aircraft Using Large Displacement, Nonlinear Material Finite Element Analysis
Federal Aviation Regulations certification criteria for transport aircraft seats require performing dynamic tests using anthropomorphic test dummies. Floor decelerations of the tests are 16g forward with the seat tracks misaligned by up to 10 degrees and 14g downward at a pitch angle of 30 degrees. In this project the dynamic response of the passenger/seat/restraint system is modeled using nonlinear finite element analysis. The interference between a dummy model and the seat is modeled using a contact interaction algorithm. This algorithm did not converge and multiple-point constraints were used to transfer the dummy\u27s inertia load. This approach was validated with the software SOMTA and then used to predict the response of a high energy absorption seat design subjected to the floor deceleration as stated in the FAR. The seat withstood the dynamic loading in both cases. The seat showed poor energy absorption characteristics when subjected to the 14g downward floor deceleration
Integrating out heavy particles with functional methods: a simplified framework
We present a systematic procedure to obtain the one-loop low-energy effective
Lagrangian resulting from integrating out the heavy fields of a given
ultraviolet theory. We show that the matching coefficients are determined
entirely by the hard region of the functional determinant involving the heavy
fields. This represents an important simplification with respect the
conventional matching approach, where the full and effective theory
contributions have to be computed separately and a cancellation of the infrared
divergent parts has to take place. We illustrate the method with a descriptive
toy model and with an extension of the Standard Model with a heavy real scalar
triplet. A comparison with other schemes that have been put forward recently is
also provided.Comment: 24 pages. Uses feynMF packag
Universal Behavior of Extreme Price Movements in Stock Markets
Many studies assume stock prices follow a random process known as geometric
Brownian motion. Although approximately correct, this model fails to explain
the frequent occurrence of extreme price movements, such as stock market
crashes. Using a large collection of data from three different stock markets,
we present evidence that a modification to the random model -- adding a slow,
but significant, fluctuation to the standard deviation of the process --
accurately explains the probability of different-sized price changes, including
the relative high frequency of extreme movements. Furthermore, we show that
this process is similar across stocks so that their price fluctuations can be
characterized by a single curve. Because the behavior of price fluctuations is
rooted in the characteristics of volatility, we expect our results to bring
increased interest to stochastic volatility models, and especially to those
that can produce the properties of volatility reported here.Comment: 4 pages, 3 figure
Lepton Flavor Non-Universality in B decays from Dynamical Yukawas
The basic features of quark and lepton mass matrices can be successfully
explained by natural minima of a generic potential with dynamical Yukawa fields
invariant under the flavor symmetry.
If this symmetry is gauged, in order to avoid potentially dangerous Goldstone
bosons, and small perturbations are added to exactly fit the observed pattern
of fermion masses, the spectrum of massive flavor gauge bosons can naturally
explain the hints for new physics in transitions,
including . In particular, the desired pattern of the Standard Model
Yukawa couplings is compatible with a gauged in the quark
sector, and in the lepton sector spontaneously
broken around the TeV scale. In order to explain the aforementioned
experimental hints, the corresponding neutral gauge bosons are required to mix,
yielding to potentially observable signals in dimuon resonance searches at the
LHC.Comment: 11 pages, 9 figures. v2: version published in Phys.Lett.
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