16,223 research outputs found
Theory of CP violation in B decays
The study of CP violation in -meson decays has already reached a high
level of precision, which will be pushed even higher in the future era of
Belle-II and the LHCb upgrade. %Important probes of CP violation are the
and mixing phases and the CKM angle . Here, the
theoretical challenge is to control the uncertainties from strong interactions
to distinguish between the Standard Model and possible New Physics effects. In
this talk, I will present a selected overview of recent theoretical
developments in this field. This includes, in particular, the semileptonic
asymmetry and extractions of the CKM angle and the
and mixing phases. I focus on recently proposed strategies in
which the theory uncertainties can be controlled through data using flavour
symmetries of the strong interaction. A newly found puzzle in the
system is highlighted and a theoretically clean way to determine the underlying
electroweak penguin parameters is discussed. Finally, the recent progress to
describe three-body decays in QCD factorization is discussed.Comment: To be published in the proceedings of The International Conference on
B-Physics at Frontier Machines - BEAUTY2018, La Biodola, Elba Island, Italy,
6-11 May, 2018 and in the proceedings of the XIV International Conference on
Heavy Quarks and Leptons (HQL2018), Yamagata, Japan, May 27- June 1, 201
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
Limits on Lorentz violation from charged-pion decay
Charged-pion decay offers many opportunities to study Lorentz violation.
Using an effective field theory approach, we study Lorentz violation in the
lepton, W-boson, and quark sectors and derive the differential pion-decay rate,
including muon polarization. Using coordinate redefinitions we are able to
relate the first-generation quark sector, in which no bounds were previously
reported, to the lepton and W-boson sector. This facilitates a tractable
calculation, enabling us to place bounds on the level of on
first-generation quark parameters. Our expression for the pion-decay rate can
be used to constrain Lorentz violation in future experiments.Comment: 12 pages, 1 figure, Accepted for publication in Phys. Rev.
The use of electron scattering for studying atomic momentum distributions: The case of graphite and diamond
The momentum distributions of C atoms in polycrystalline diamond (produced by chemical vapor deposition) and in highly oriented pyrolitic graphite (HOPG) are studied by scattering of 40 keV electrons at 135°. By measuring the Doppler broadening of the energy of the elastically scattered electrons, we resolve a Compton profile of the motion of the C atoms. The aim of the present work is to resolve long-standing disagreements between the calculated kinetic energies of carbon atoms in HOPG and in diamond films and the measured ones, obtained both by neutron Compton scattering (NCS) and by nuclear resonance photon scattering (NRPS). The anisotropy of the momentum distribution in HOPG was measured by rotating the HOPG sample relative to the electron beam. The obtained kinetic energies for the motion component along, and perpendicular to, the graphite planes were somewhat higher than those obtained from the most recent NCS data of HOPG. Monte Carlo simulations indicate that multiple scattering adds about 2% to the obtained kinetic energies. The presence of different isotopes in carbon affects the measurement at a 1% level. After correcting for these contributions, the kinetic energies are 3%-6% larger than the most recent NCS results for HOPG, but 15%-25% smaller than the NRPS results. For diamond, the corrected direction-averaged kinetic energy is ≈ 6% larger than the calculated value. This compares favorably to the ≈25% discrepancy between theory and both the NCS and NRPS results for diamond.This work is made possible
by a grant of the Australian Research Council
A Birkhoff connection between quantum circuits and linear classical reversible circuits
Birkhoff's theorem tells how any doubly stochastic matrix can be decomposed as a weighted sum of permutation matrices. Similar theorems on unitary matrices reveal a connection between quantum circuits and linear classical reversible circuits. It triggers the question whether a quantum computer can be regarded as a superposition of classical reversible computers
Towards New Frontiers with Decays
Exploring correlations between the CP asymmetries of
following from an isospin relation, we uncover new tensions with the Standard
Model in data for neutral decays. Should this intriguing picture
originate from New Physics, a modified electroweak penguin sector provides a
key scenario. It includes models with extra bosons, which offer attractive
ways to resolve anomalies in measurements. We
present a new strategy to reveal the underlying physics, apply it to current
data, and discuss the excellent prospects for Belle II.Comment: 7 pages, 3 figure
determination from inclusive decays: an alternative method
The determination of relies on the Heavy-Quark Expansion and the
extraction of the non-perturbative matrix elements from inclusive
decays. The proliferation of these matrix elements complicates their extraction
at and higher, thereby limiting the extraction.
Reparametrization invariance links different operators in the Heavy-Quark
expansion thus reducing the number of independent operators at to
eight for the total rate. We show that this reduction also holds for spectral
moments as long as they are defined by reparametrization invariant
weight-functions. This is valid in particular for the leptonic invariant mass
spectrum (), i.e. the differential rate and its moments. Currently,
is determined by fitting the energy and hadronic mass moments, which
do not manifest this parameter reduction and depend on the full set of 13
matrix elements up to . In light of this, we propose an experimental
analysis of the moments to open the possibility of a model-independent
extraction from semileptonic decays including the terms in a
fully data-driven way.Comment: 16 pages, 2 figures. v2: version published in JHEP, references added
plus minor change
Limits on Lorentz violation in neutral-Kaon decay
The KLOE collaboration recently reported bounds on the directional dependence
of the lifetime of the short-lived neutral kaon K_S with respect to the cosmic
microwave background dipole anisotropy. We interpret their results in a general
framework developed to probe Lorentz violation in the weak interaction. In this
approach a Lorentz-violating tensor \chi_{\mu\nu} is added to the standard
propagator of the W boson. We derive the K_S decay rate in a naive tree-level
model and calculate the asymmetry for the lifetime. By using the KLOE data the
real vector part of \chi_{\mu\nu} is found to be smaller than 10^-2. We briefly
discuss the theoretical challenges concerning nonleptonic decays.Comment: Presented at the Sixth Meeting on CPT and Lorentz Symmetry,
Bloomington, Indiana, June 17-21, 2013
Testing Lorentz invariance in orbital electron capture
Searches for Lorentz violation were recently extended to the weak sector, in
particular neutron and nuclear decay [1]. From experiments on forbidden
-decay transitions strong limits in the range of -
were obtained on Lorentz-violating components of the -boson propagator [2].
In order to improve on these limits strong sources have to be considered. In
this Brief Report we study isotopes that undergo orbital electron capture and
allow experiments at high decay rates and low dose. We derive the expressions
for the Lorentz-violating differential decay rate and discuss the options for
competitive experiments and their required precision.Comment: accepted for publication as a Brief Report in Physical Review
Symmetry violations in nuclear and neutron decay
The role of decay as a low-energy probe of physics beyond the
Standard Model is reviewed. Traditional searches for deviations from the
Standard Model structure of the weak interaction in decay are discussed
in the light of constraints from the LHC and the neutrino mass. Limits on the
violation of time-reversal symmetry in decay are compared to the strong
constraints from electric dipole moments. Novel searches for Lorentz symmetry
breaking in the weak interaction in decay are also included, where we
discuss the unique sensitivity of decay to test Lorentz invariance. We
end with a roadmap for future -decay experiments.Comment: Accepted for publication in Rev. Mod. Phys. 86 pages, 13 figure
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