58 research outputs found
Pseudo-neutrino versus recoil formalism for 4-body phase space and applications to nuclear decay
It is well-known that the traditional treatment of radiative corrections that
utilizes the "true" neutrino momentum in the differential decay
rate formula could lead to a systematic error in certain
observables due to the mistreatment of 4-body kinematics. We investigate the
theory structure of one of the proposed solutions, the "-formalism", in
the non-recoil limit appropriate for neutron and nuclear beta decays. We derive
an elegant master formula for the 4-body phase space and use it to re-analyze
the spectrum-dependent "outer" radiative corrections to the beta decay of a
polarized spin-half nucleus; a complete set of analytic expressions is provided
for readers to straightforwardly obtain the final numerical results. We compare
it to the "recoil formalism" where the energy of the recoil nucleus is fixed.Comment: Version accepted by PR
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Hadron Physics in Tests of Fundamental Symmetries
Low energy precision tests of fundamental symmetries provide excellent probes for the Beyond Standard Model Physics. Theoretical interpretations of these experiments often involve the application of non-perturbative Quantum Chromodynamics in the study of hadronic matrix elements that may either serve as signals of new physics or Standard Model backgrounds. In this work I present a series of studies on different hadronic matrix elements using various low-energy effective approaches to Quantum Chromodynamics, and discuss the impact of these studies on our knowledge of Standard Model and Beyond Standard Model physics
Model-independent determination of nuclear weak form factors and implications for Standard Model precision tests
We analyze the recoil corrections in superallowed beta decays of ,
nuclei by fixing the mean square charge weak radius
model-independently using the data of multiple charge radii across the nuclear
isotriplet. By comparing to model estimations, we argue that the existing
theory uncertainty in the statistical rate function might have been
substantially underestimated. We discuss the implications of our proposed
strategy for precision tests of Standard Model, including a potential
alleviation of the first-row CKM unitarity deficit, and motivate new
experiments for charge radii measurements.Comment: Version accepted by PR
Toward a First-Principles Calculation of Electroweak Box Diagrams
We derive a Feynman-Hellmann theorem relating the second-order nucleon energy
shift resulting from the introduction of periodic source terms of
electromagnetic and isovector axial currents to the parity-odd nucleon
structure function . It is a crucial ingredient in the theoretical study
of the and box diagrams that are known to suffer from
large hadronic uncertainties. We demonstrate that for a given , one only
needs to compute a small number of energy shifts in order to obtain the
required inputs for the box diagrams. Future lattice calculations based on this
approach may shed new light on various topics in precision physics including
the refined determination of the Cabibbo-Kobayashi-Maskawa matrix elements and
the weak mixing angle.Comment: Version to appear in PR
Effective Field Theory in The Study of Long Range Nuclear Parity Violation on Lattice
A non-zero signal of
the gamma-ray asymmetry in the neutron-proton capture was recently reported by
the NPDGamma Collaboration which provides the first determination of the
parity-odd pion-nucleon coupling constant . The ability to reproduce this value from first principles
serves as a direct test of our current understanding of the interplay between
the strong and weak interaction at low energy. To motivate new lattice studies
of , we review the current status of the theoretical understanding of
this coupling, which includes our recent work that relates it to a nucleon
mass-splitting by a soft-pion theorem. We further investigate the possibility
of calculating the mass-splitting on the lattice by providing effective field
theory parameterizations of all the involved quark contraction diagrams. We
show that the lattice calculations of the easier connected diagrams will
provide information of the chiral logarithms in the much harder quark loop
diagrams and thus help in the chiral extrapolation of the latter.Comment: 43 pages, 3 figures, 1 table. Accepted by EPJ
Towards - nuclear theory calculations of
We propose a new theory framework to study the isospin-symmetry breaking
correction in superallowed nuclear beta decays, crucial for
the precise determination of . Based on a general assumptions of the
isovector dominance in ISB interactions, we construct a set of functions
which involve nuclear matrix elements of isovector monopole operators
and the nuclear Green's function. Via the functions , a connection of
to measurable electroweak nuclear radii is established,
providing an experimental gauge of the theory accuracy of . We
outline a strategy to perform ab-initio calculations of based on the
Lanczos algorithm, and discuss its similarity with other
nuclear-structure-dependent inputs in nuclear beta decays.Comment: 8 pages, 1 tabl
Dispersion relation analysis of the radiative corrections to in the neutron -decay
We present the first and complete dispersion relation analysis of the inner
radiative corrections to the axial coupling constant in the neutron
-decay. Using experimental inputs from the elastic form factors and the
spin-dependent structure function , we determine the contribution from the
-box diagram to a precision better than . Our calculation
indicates that the inner radiative corrections to the Fermi and the
Gamow-Teller matrix element in the neutron -decay are almost identical,
i.e. the ratio is almost unrenormalized. With this result, we
predict the bare axial coupling constant to be
{} based on the PDG
average Comment: Revised manuscrip
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