12,526 research outputs found
Lepton flavor violating Higgs boson decays in seesaw models: new discussions
The lepton flavor violating decay of the Standard Model-like Higgs boson
(LFVHD), h->\mu\tau, is discussed in seesaw models at the one-loop level. Based
on particular analytic expressions of Passarino-Veltman functions, the two
unitary and 't Hooft Feynman gauges are used to compute the branching ratio of
LFVHD and compare with results reported recently. In the minimal seesaw (MSS)
model, the branching ratio was investigated in the whole valid range
10^{-9}-10^{15} GeV of new neutrino mass scale m_{n_6}. Using the Casas-Ibarra
parameterization, this branching ratio enhances with large and increasing
m_{n_6}. But the maximal value can reach only order of 10^{-11}. Interesting
relations of LFVHD predicted by the MSS and inverse seesaw (ISS) model are
discussed. The ratio between two LFVHD branching ratios predicted by the ISS
and MSS is simply m^2_{n_6}\mu^{-2}_X, where \mu_X is the small neutrino mass
scale in the ISS. The consistence between different calculations is shown
precisely from analytical approach.Comment: 4 figures, 26 pages, some analytic formulas and statements are
corrected. Main results are unchanged. New references added. Version
published in NP
Quantum Spin Dynamics with Pairwise-Tunable, Long-Range Interactions
We present a platform for the simulation of quantum magnetism with full
control of interactions between pairs of spins at arbitrary distances in one-
and two-dimensional lattices. In our scheme, two internal atomic states
represent a pseudo-spin for atoms trapped within a photonic crystal waveguide
(PCW). With the atomic transition frequency aligned inside a band gap of the
PCW, virtual photons mediate coherent spin-spin interactions between lattice
sites. To obtain full control of interaction coefficients at arbitrary
atom-atom separations, ground-state energy shifts are introduced as a function
of distance across the PCW. In conjunction with auxiliary pump fields,
spin-exchange versus atom-atom separation can be engineered with arbitrary
magnitude and phase, and arranged to introduce non-trivial Berry phases in the
spin lattice, thus opening new avenues for realizing novel topological spin
models. We illustrate the broad applicability of our scheme by explicit
construction for several well known spin models.Comment: 18 pages, 10 figure
Quantum many-body models with cold atoms coupled to photonic crystals
Using cold atoms to simulate strongly interacting quantum systems represents
an exciting frontier of physics. However, as atoms are nominally neutral point
particles, this limits the types of interactions that can be produced. We
propose to use the powerful new platform of cold atoms trapped near
nanophotonic systems to extend these limits, enabling a novel quantum material
in which atomic spin degrees of freedom, motion, and photons strongly couple
over long distances. In this system, an atom trapped near a photonic crystal
seeds a localized, tunable cavity mode around the atomic position. We find that
this effective cavity facilitates interactions with other atoms within the
cavity length, in a way that can be made robust against realistic
imperfections. Finally, we show that such phenomena should be accessible using
one-dimensional photonic crystal waveguides in which coupling to atoms has
already been experimentally demonstrated
A new mechanism for a naturally small Dirac neutrino mass
A mechanism is proposed in which a right-handed neutrino zero mode and a
right-handed charged lepton zero mode can be localized at the same place along
an extra compact dimension while having markedly different spreads in their
wave functions: a relatively narrow one for the neutrino and a rather broad one
for the charged lepton. In their overlaps with the wave function for the
left-handed zero modes, this mechanism could produce a natural large hierarchy
in the effective Yukawa couplings in four dimensions, and hence a large
disparity in masses.Comment: 6 pages (2 with figures), twocolumn forma
Quasi-local mass in the covariant Newtonian space-time
In general relativity, quasi-local energy-momentum expressions have been
constructed from various formulae. However, Newtonian theory of gravity gives a
well known and an unique quasi-local mass expression (surface integration).
Since geometrical formulation of Newtonian gravity has been established in the
covariant Newtonian space-time, it provides a covariant approximation from
relativistic to Newtonian theories. By using this approximation, we calculate
Komar integral, Brown-York quasi-local energy and Dougan-Mason quasi-local mass
in the covariant Newtonian space-time. It turns out that Komar integral
naturally gives the Newtonian quasi-local mass expression, however, further
conditions (spherical symmetry) need to be made for Brown-York and Dougan-Mason
expressions.Comment: Submit to Class. Quantum Gra
Sloshing dynamics modulated fluid angular momentum and moment fluctuations driven by orbital gravity gradient and jitter accelerations in microgravity
The dynamical behavior of spacecraft propellant affected by the asymmetric combined gravity gradient and jitter accelerations, in particular the effect of surface tension on partially-filled rotating fluids applicable to a full-scale Gravity Probe-B Spacecraft dewar tank has been investigated. Three different cases of orbital accelerations: (1) gravity gradient-dominated, (2) equally weighted between gravity gradient and jitter, and (3) gravity jitter-dominated accelerations are studied. The results of slosh wave excitation along the liquid-vapor interface induced by gravity gradient-dominated accelerations provide a torsional moment with tidal motion of bubble oscillations in the rotating dewar. The results are clearly seen from the twisting shape of the bubble oscillations driven by gravity gradient-dominated acceleration. The results of slosh wave excitation along the liquid-vapor interface induced by gravity jitter-dominated acceleration indicate the results of bubble motion in a manner of down-and-up and leftward-and-rightward movement of oscillation when the bubble is rotating with respect to rotating dewar axis. Fluctuations of angular momentum, fluid moment and bubble mass center caused by slosh wave excitations driven by gravity gradient acceleration or gravity jitter acceleration are also investigated
Three-dimensional transient flow of spin-up in a filled cylinder with oblique gravity force
Three-dimensional transient flow profiles of spin-up in a fully liquid filled cylinder from rest with gravity acceleration at various direction are numerically simulated and studied. Particular interests are concentrated on the development of temporary reverse flow zones and Ekman layer right after the impulsive start of spin-up from rest, and decay before the flow reaching to the solid rotation. Relationship of these flow developments and differences in the Reynolds numbers of the flow and its size selection of grid points concerning the numerical instabilities of flow computations are also discussed. In addition to the gravitational acceleration along the axial direction of the cylindrical container, a series of complicated flow profiles accompanied by three-dimensional transient flows with oblique gravitational acceleration has been studies
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