1,966 research outputs found
Proposed method for laser spectroscopy of pionic helium atoms to determine the charged-pion mass
Metastable pionic helium () is a three-body atom composed of a
helium nucleus, an electron occupying the ground state, and a negatively
charged pion in a Rydberg state with principal- and orbital angular
momentum quantum numbers of . We calculate the
spin-independent energies of the and
isotopes in the region --19. These include relativistic and quantum
electrodynamics corrections of orders and
in atomic units, where and denote
the Rydberg and fine structure constants. The fine-structure splitting due to
the coupling between the electron spin and the orbital angular momentum of the
, and the radiative and Auger decay rates of the states are also
calculated. Some states and retain
nanosecond-scale lifetimes against absorption into the helium nucleus.
We propose to use laser pulses to induce transitions from these
metastable states, to states with large ( s) Auger rates.
The ion that remains after Auger emission of the
electron undergoes Stark mixing with the , , and states during
collisions with the helium atoms in the experimental target. This leads to
immediate nuclear absorption of the . The resonance condition between
the laser beam and the atom is thus revealed as a sharp spike in the rates of
neutrons, protons, deuterons, and tritons that emerge....(continued)Comment: 25 pages, 3 tables, 11 figure
Density-Matrix Renormalization Group Study of Trapped Imbalanced Fermi Condensates
The density-matrix renormalization group is employed to investigate a
harmonically-trapped imbalanced Fermi condensate based on a one-dimensional
attractive Hubbard model. The obtained density profile shows a flattened
population difference of spin-up and spin-down components at the center of the
trap, and exhibits phase separation between the condensate and unpaired
majority atoms for a certain range of the interaction and population imabalance
. The two-particle density matrix reveals that the sign of the order
parameter changes periodically, demonstrating the realization of the
Fulde-Ferrell-Larkin-Ovchinnikov phase. The minority spin atoms contribute to
the quasi-condensate up to at least . Possible experimental
situations to test our predictions are discussed.Comment: 4 pages, 3 figures; added references; accepted for publication in
Phys. Rev. Let
Exotic branes and non-geometric backgrounds
When string/M-theory is compactified to lower dimensions, the U-duality
symmetry predicts so-called exotic branes whose higher dimensional origin
cannot be explained by the standard string/M-theory branes. We argue that
exotic branes can be understood in higher dimensions as non-geometric
backgrounds or U-folds, and that they are important for the physics of systems
which originally contain no exotic charges, since the supertube effect
generically produces such exotic charges. We discuss the implications of exotic
backgrounds for black hole microstate (non-)geometries.Comment: 4 pages. v2: journal version. The discussion on "double puff-up"
revise
Dynamics of one-dimensional Bose liquids: Andreev-like reflection at Y-junctions and absence of the Aharonov-Bohm effect
We study one dimensional Bose liquids of interacting ultracold atoms in the
Y-shaped potential when each branch is filled with atoms. We find that the
excitation packet incident on a single Y-junction should experience a negative
density reflection analogous to the Andreev reflection at normal-superconductor
interfaces, although the present system does not contain fermions. In a ring
interferometer type configuration, we find that the transport is completely
insensitive to the (effective) flux contained in the ring, in contrast to the
Aharonov-Bohm effect of a single particle in the same geometry.Comment: 4 pages, 2 figures, final versio
Calculation of transition probabilities and ac Stark shifts in two-photon laser transitions of antiprotonic helium
Numerical ab initio variational calculations of the transition probabilities
and ac Stark shifts in two-photon transitions of antiprotonic helium atoms
driven by two counter-propagating laser beams are presented. We found that
sub-Doppler spectroscopy is in principle possible by exciting transitions of
the type (n,L)->(n-2,L-2) between antiprotonic states of principal and angular
momentum quantum numbers n~L-1~35, first by using highly monochromatic,
nanosecond laser beams of intensities 10^4-10^5 W/cm^2, and then by tuning the
virtual intermediate state close (e.g., within 10-20 GHz) to the real state
(n-1,L-1) to enhance the nonlinear transition probability. We expect that ac
Stark shifts of a few MHz or more will become an important source of systematic
error at fractional precisions of better than a few parts in 10^9. These shifts
can in principle be minimized and even canceled by selecting an optimum
combination of laser intensities and frequencies. We simulated the resonance
profiles of some two-photon transitions in the regions n=30-40 of the
\bar{p}^4He^+ and \bar{p} ^3He^+ isotopes to find the best conditions that
would allow this.Comment: 18 pages 2 tables 12 figures, submitted to Phys. Rev.
Boundary Critical Phenomena in SU(3) "Spin" Chains
SU(3)-invariant "spin" chains with a single impurity, such as a modified
exchange coupling on one link, are analyzed using boundary conformal field
theory techniques. These chains are equivalent to a special case of the "tJV"
model, i.e. the t-J model with a nearest neighbour repulsion added. In the
continuum limit they are equivalent to two free bosons at a special value of
the compactification radii. The SU(3) symmetry, which is made explicit in this
formulation, provides insight into the exact solution of a non-trivial boundary
critical point found earlier in another formulation of this model as a theory
of quantum Brownian motion.Comment: 19 pages, Rev Te
Mesospheric anomalous diffusion during noctilucent clouds
The Andenes specular meteor radar shows meteor-trail diffusion rates increasing on average by ~ 20% at times and locations where a lidar observes noctilucent clouds (NLCs). This high-latitude effect has been attributed to the presence of charged NLC but this study shows that such behaviors result predominantly from thermal tides. To make this claim, the current study evaluates data from three stations, at high-, mid-, and low-latitudes, for the years 2012 to 2016, comparing diffusion to show that thermal tides correlate strongly with the presence of NLCs. This data also shows that the connection between meteor-trail diffusion and thermal tide occurs at all altitudes in the mesosphere, while the NLC influence exists only at high-latitudes and at around peak of NLC layer. This paper discusses a number of possible explanations for changes in the regions with NLCs and leans towards the hypothesis that relative abundance of background electron density plays the leading role. A more accurate model of the meteor trail diffusion around NLC particles would help researchers determine mesospheric temperature and neutral density profiles from meteor radars.Public versio
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