170 research outputs found
Neutrinoless double beta decay in effective field theory
We discuss the contributions of lepton-number-violating sources to
neutrinoless double beta decay (). Assuming that these sources
arise at scales well above the electroweak scale, they can be described within
an effective field theory. Here, we outline the steps required to express the
half-life in terms of the effective interactions, focusing on
the dimension-five operator that induces a Majorana mass for the neutrinos.
This process involves the evolution of the operators down to scales of a few
GeV where they can be matched onto Chiral Perturbation Theory. The resulting
Chiral Lagrangian can then used be to derive the lepton-number violating
potential, which, in combination with many-body methods, gives the
half-life. We will show that consistent renormalization
requires the inclusion of a new contact interaction at leading order in this
potential. We also briefly comment on the constraints that can be set on the
operators appearing beyond dimension five.Comment: Corrected referenc
High- and low-energy constraints on top-Higgs couplings
We study the five chirality-flipping interactions that appear in the
top-Higgs sector at leading order in the standard model effective field theory.
We consider constraints from collider observables, flavor physics, and
electric-dipole-moment experiments. This analysis results in very competitive
constraints from indirect observables when one considers a single coupling at a
time. In addition, we discuss how these limits are affected in scenarios in
which multiple top-Higgs interactions are generated at the scale of new
physics.Comment: 7 pages, 1 figure. Contribution to the proceedings of the 9th
International Workshop on the CKM Unitarity Triangle, 28 November - 3
December 201
Renormalization Group Running of Dimension-Six Sources of Parity and Time-Reversal Violation
We perform a systematic study of flavor-diagonal parity- and
time-reversal-violating operators of dimension six which could arise from
physics beyond the SM. We begin at the unknown high-energy scale where these
operators originate. At this scale the operators are constrained by gauge
invariance which has important consequences for the form of effective operators
at lower energies. In particular for the four-quark operators. We calculate
one-loop QCD and, when necessary, electroweak corrections to the operators and
evolve them down to the electroweak scale and subsequently to hadronic scales.
We find that for most operators QCD corrections are not particularly
significant. We derive a set of operators at low energy which is expected to
dominate hadronic and nuclear EDMs due to physics beyond the SM and obtain
quantitative relations between these operators and the original dimension-six
operators at the high-energy scale. We use the limit on the neutron EDM to set
bounds on the dimension-six operators.Comment: Matches published version, 35 pages, 6 figures, minor correction
T violation in radiative decay and electric dipole moments
In radiative decay, violation can be studied through a
spin-independent -odd correlation. We consider contributions to this
correlation by beyond the standard model (BSM) sources of -violation,
arising above the electroweak scale. At the same time such sources,
parametrized by dimension-6 operators, can induce electric dipole moments
(EDMs). As a consequence, the manifestations of the -odd BSM physics in
radiative decay and EDMs are not independent. Here we exploit this
connection to show that current EDM bounds already strongly constrain the
spin-independent -odd correlation in radiative decay.Comment: 11 pages, 2 figure
Neutrinoless double beta decay in effective field theory: the light Majorana neutrino exchange mechanism
We present the first chiral effective theory derivation of the neutrinoless
double beta-decay potential induced by light Majorana
neutrino exchange. The effective-field-theory framework has allowed us to
identify and parameterize short- and long-range contributions previously missed
in the literature. These contributions can not be absorbed into
parameterizations of the single nucleon form factors. Starting from the quark
and gluon level, we perform the matching onto chiral effective field theory and
subsequently onto the nuclear potential. To derive the nuclear potential
mediating neutrinoless double beta-decay, the hard, soft and potential neutrino
modes must be integrated out. This is performed through next-to-next-to-leading
order in the chiral power counting, in both the Weinberg and pionless schemes.
At next-to-next-to-leading order, the amplitude receives additional
contributions from the exchange of ultrasoft neutrinos, which can be expressed
in terms of nuclear matrix elements of the weak current and excitation energies
of the intermediate nucleus. These quantities also control the two-neutrino
double beta-decay amplitude. Finally, we outline strategies to determine the
low-energy constants that appear in the potentials, by relating them to
electromagnetic couplings and/or by matching to lattice QCD calculations.Comment: 20 pages, 6 figure
The phenomenology of electric dipole moments in models of scalar leptoquarks
We study the phenomenology of electric dipole moments (EDMs) induced in
various scalar leptoquark models. We consider generic leptoquark couplings to
quarks and leptons and match to Standard Model effective field theory. After
evolving the resulting operators to low energies, we connect to EDM experiments
by using up-to-date hadronic, nuclear, and atomic matrix elements. We show that
current experimental limits set strong constraints on the possible CP-violating
phases in leptoquark models. Depending on the quarks and leptons involved in
the interaction, the existing searches for EDMs of leptons, nucleons, atoms,
and molecules all play a role in constraining the CP-violating couplings. We
discuss the impact of hadronic and nuclear uncertainties as well as the
sensitivities that can be achieved with future EDM experiments. Finally, we
study the impact of EDM constraints on a specific leptoquark model that can
explain the recent -physics anomalies.Comment: Published versio
Right-handed charged currents in the era of the Large Hadron Collider
We discuss the phenomenology of right-handed charged currents in the
framework of the Standard Model Effective Field Theory, in which they arise due
to a single gauge-invariant dimension-six operator. We study the manifestations
of the nine complex couplings of the to right-handed quarks in collider
physics, flavor physics, and low-energy precision measurements. We first obtain
constraints on the couplings under the assumption that the right-handed
operator is the dominant correction to the Standard Model at observable
energies. We subsequently study the impact of degeneracies with other
Beyond-the-Standard-Model effective interactions and identify observables, both
at colliders and low-energy experiments, that would uniquely point to
right-handed charged currents.Comment: 50 pages plus appendices and reference
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