4,291 research outputs found
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.
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
D-branes in Topological Minimal Models: the Landau-Ginzburg Approach
We study D-branes in topologically twisted N=2 minimal models using the
Landau-Ginzburg realization. In the cases of A and D-type minimal models we
provide what we believe is an exhaustive list of topological branes and compute
the corresponding boundary OPE algebras as well as all disk correlators. We
also construct examples of topological branes in E-type minimal models. We
compare our results with the boundary state formalism, where possible, and find
agreement.Comment: 29 pages, late
D-brane Categories for Orientifolds -- The Landau-Ginzburg Case
We construct and classify categories of D-branes in orientifolds based on
Landau-Ginzburg models and their orbifolds. Consistency of the worldsheet
parity action on the matrix factorizations plays the key role. This provides
all the requisite data for an orientifold construction after embedding in
string theory. One of our main results is a computation of topological field
theory correlators on unoriented worldsheets, generalizing the formulas of Vafa
and Kapustin-Li for oriented worldsheets, as well as the extension of these
results to orbifolds. We also find a doubling of Knoerrer periodicity in the
orientifold context.Comment: 45 pages, 6 figure
Permutation branes and linear matrix factorisations
All the known rational boundary states for Gepner models can be regarded as
permutation branes. On general grounds, one expects that topological branes in
Gepner models can be encoded as matrix factorisations of the corresponding
Landau-Ginzburg potentials. In this paper we identify the matrix factorisations
associated to arbitrary B-type permutation branes.Comment: 43 pages. v2: References adde
Orientifolds of Gepner Models
We systematically construct and study Type II Orientifolds based on Gepner
models which have N=1 supersymmetry in 3+1 dimensions. We classify the parity
symmetries and construct the crosscap states. We write down the conditions that
a configuration of rational branes must satisfy for consistency (tadpole
cancellation and rank constraints) and spacetime supersymmetry. For certain
cases, including Type IIB orientifolds of the quintic and a two parameter
model, one can find all solutions in this class. Depending on the parity, the
number of vacua can be large, of the order of 10^{10}-10^{13}. For other
models, it is hard to find all solutions but special solutions can be found --
some of them are chiral. We also make comparison with the large volume regime
and obtain a perfect match. Through this study, we find a number of new
features of Type II orientifolds, including the structure of moduli space and
the change in the type of O-planes under navigation through non-geometric
phases.Comment: 142 page
Orientifolds and Mirror Symmetry
We study parity symmetries and crosscap states in classes of N=2
supersymmetric quantum field theories in 1+1 dimensions, including non-linear
sigma models, gauged WZW models, Landau-Ginzburg models, and linear sigma
models. The parity anomaly and its cancellation play important roles in many of
them. The case of the N=2 minimal model are studied in complete detail, from
all three realizations -- gauged WZW model, abstract RCFT, and LG models. We
also identify mirror pairs of orientifolds, extending the correspondence
between symplectic geometry and algebraic geometry by including unorientable
worldsheets. Through the analysis in various models and comparison in the
overlapping regimes, we obtain a global picture of orientifolds and D-branes.Comment: 137 page
Bulk perturbations of N=2 branes
The evolution of supersymmetric A-type D-branes under the bulk
renormalization group flow between two different N=2 minimal models is studied.
Using the Landau-Ginzburg description we show that a specific set of branes
decouples from the infrared theory, and we make detailed predictions for the
behavior of the remaining branes. The Landau-Ginzburg picture is then checked
against a direct conformal field theory analysis. In particular we construct a
natural index pairing which is preserved by the RG flow, and show that the
branes that decouple have vanishing index with the surviving branes.Comment: 35 pages (30 pages plus title and references), 8 figure
Integrability of the N=2 boundary sine-Gordon model
We construct a boundary Lagrangian for the N=2 supersymmetric sine-Gordon
model which preserves (B-type) supersymmetry and integrability to all orders in
the bulk coupling constant g. The supersymmetry constraint is expressed in
terms of matrix factorisations.Comment: LaTeX, 19 pages, no figures; v2: title changed, minor improvements,
refs added, to appear in J. Phys. A: Math. Ge
Worldsheet Matter Superfields on Half-Shell
In this paper we discuss some of the effects of using "unidexterous"
worldsheet superfields, which satisfy worldsheet differential constraints and
so are partly on-shell, i.e., on half-shell. Most notably, this results in a
stratification of the field space that reminds of "brane-world" geometries.
Linear dependence on such superfields provides a worldsheet generalization of
the super-Zeeman effect. In turn, non-linear dependence yields additional
left-right asymmetric dynamical constraints on the propagating fields, again in
a stratified fashion.Comment: 15 pages, 2 figures; minor algebraic correction
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