3,108 research outputs found
Observational Constraints on Secret Neutrino Interactions from Big Bang Nucleosynthesis
We investigate possible interactions between neutrinos and massive scalar
bosons via (or massive vector bosons via
) and explore the allowed
parameter space of the coupling constant (or ) and the
scalar (or vector) boson mass (or ) by requiring that these
secret neutrino interactions (SNIs) should not spoil the success of Big Bang
nucleosynthesis (BBN). Incorporating the SNIs into the evolution of the early
Universe in the BBN era, we numerically solve the Boltzmann equations and
compare the predictions for the abundances of light elements with observations.
It turns out that the constraint on and in the
scalar-boson case is rather weak, due to a small number of degrees of freedom.
However, in the vector-boson case, the most stringent bound on the coupling
at confidence level is obtained for
, while the bound becomes much weaker for smaller masses . Moreover, we discuss in some detail how the SNIs affect the cosmological
evolution and the abundances of the lightest elements.Comment: 18 pages, 5 figure
Renormalization Group Approach to Stability of Two-dimensional Interacting Type-II Dirac Fermions
The type-II Weyl/Dirac fermions are a generalization of conventional or
type-I Weyl/Dirac fermions, whose conic spectrum is tilted such that the Fermi
surface becomes lines in two dimensions, and surface in three dimensions rather
than discrete points of the conventional Weyl/Dirac fermions. The
mass-independent renormalization group calculations show that the tilting
parameter decreases monotonically with respect to the length scale, which leads
to a transition from two dimensional type-II Weyl/Dirac fermions to the type-I
ones. Because of the non-trivial Fermi surface, a photon gains a finite mass
partially via the chiral anomaly, leading to the strong screening effect of the
Weyl/Dirac fermions. Consequently, anisotropic type-II Dirac semimetals become
stable against the Coulomb interaction. This work provides deep insight into
the interplay between the geometry of Fermi surface and the Coulomb
interaction.Comment: Final pulished versio
Topological responses from chiral anomaly in multi-Weyl semimetals
Multi-Weyl semimetals are a kind of topological phase of matter with discrete
Weyl nodes characterized by multiple monopole charges, in which the chiral
anomaly, the anomalous nonconservation of an axial current, occurs in the
presence of electric and magnetic fields. Electronic transport properties
related to the chiral anomaly in the presence of both electromagnetic fields
and axial electromagnetic fields in multi-Weyl semimetals are systematically
studied. It has been found that the anomalous Hall conductivity has a
modification linear in the axial vector potential from inhomogeneous strains.
The axial electric field leads to an axial Hall current that is proportional to
the distance of Weyl nodes in momentum space. This axial current may generate
chirality accumulation of Weyl fermions through delicately engineering the
axial electromagnetic fields even in the absence of external electromagnetic
fields. Therefore, this work provides a nonmagnetic mechanism of generation of
chirality accumulation in Weyl semimetals and might shed new light on the
application of Weyl semimetals in the emerging field of valleytronics.Comment: 13 pages, 2 tables, 2 figures, accepted by Physical Review
The Mikheyev-Smirnov-Wolfenstein Matter Potential at the One-loop Level in the Standard Model
When neutrinos are propagating in ordinary matter, their coherent forward
scattering off background particles results in the so-called
Mikheyev-Smirnov-Wolfenstein (MSW) matter potential, which plays an important
role in neutrino flavor conversions. In this paper, we present a complete
one-loop calculation of the MSW matter potential in the Standard Model (SM).
First, we carry out the one-loop renormalization of the SM in the on-shell
scheme, where the electromagnetic fine-structure constant , the weak
gauge-boson masses and , the Higgs-boson mass and the
fermion masses are chosen as input parameters. Then, the finite
corrections to the scattering amplitudes of neutrinos with the electrons and
quarks are calculated, and the one-loop MSW matter potentials are derived.
Adopting the latest values of all physical parameters, we find that the
relative size of one-loop correction to the charged-current matter potential of
electron-type neutrinos or antineutrinos turns out to be , whereas that to
the neutral-current matter potential of all-flavor neutrinos or antineutrinos
can be as large as . The calculations are also performed in the
scheme and compared with previous results in the
literature.Comment: 33 pages, 12 figures, 3 tables, more discussions and references
added, version accepted by PR
Development of Computer Vision-Enhanced Smart Golf Ball Retriever
An automatic vehicle system was developed to assist golfers in collecting golf balls from a practice field. Computer vision methodology was utilized to enhance the detection of golf balls in shallow and/or deep grass regions. The free software OpenCV was used in this project because of its powerful features and supported repository. The homemade golf ball picker was built with a smart recognition function for golf balls and can lock onto targets by itself. A set of field tests was completed in which the rate of golf ball recognition was as high as 95%. We report that this homemade smart golf ball picker can reduce the tremendous amount of labor associated with having to gather golf balls scattered throughout a practice field
Tentative sensitivity of future -decay experiments to neutrino masses and Majorana CP phases
In the near future, the neutrinoless double-beta () decay
experiments will hopefully reach the sensitivity of a few to the
effective neutrino mass . In this paper, we tentatively
examine the sensitivity of future -decay experiments to
neutrino masses and Majorana CP phases by following the Bayesian statistical
approach. Provided experimental setups corresponding to the sensitivity of
, the null observation of
decays in the case of normal neutrino mass ordering leads to a
very competitive bound on the lightest neutrino mass . Namely, the
credible interval turns out to be or when the uniform prior on or on
is adopted. Moreover, one of two Majorana CP
phases is strictly constrained, i.e., for both priors of . In contrast, if a relatively worse
sensitivity of is assumed, the
constraint becomes accordingly or , while two Majorana CP
phases will be essentially unconstrained. In the same statistical framework,
the prospects for the determination of neutrino mass ordering and the
discrimination between Majorana and Dirac nature of massive neutrinos in the
-decay experiments are also discussed. Given the experimental
sensitivity of (or ),
the strength of evidence to exclude the Majorana nature under the null
observation of decays is found to be inconclusive (or strong),
no matter which of two priors on is taken.Comment: 17 pages, 4 figures, more discussions added, matches the published
version in JHE
- …