105,259 research outputs found
Ultrafast effective multi-level atom method for primordial hydrogen recombination
Cosmological hydrogen recombination has recently been the subject of renewed
attention because of its importance for predicting the power spectrum of cosmic
microwave background anisotropies. It has become clear that it is necessary to
account for a large number n >~ 100 of energy shells of the hydrogen atom,
separately following the angular momentum substates in order to obtain
sufficiently accurate recombination histories. However, the multi-level atom
codes that follow the populations of all these levels are computationally
expensive, limiting recent analyses to only a few points in parameter space. In
this paper, we present a new method for solving the multi-level atom
recombination problem, which splits the problem into a computationally
expensive atomic physics component that is independent of the cosmology, and an
ultrafast cosmological evolution component. The atomic physics component
follows the network of bound-bound and bound-free transitions among excited
states and computes the resulting effective transition rates for the small set
of "interface" states radiatively connected to the ground state. The
cosmological evolution component only follows the populations of the interface
states. By pre-tabulating the effective rates, we can reduce the recurring cost
of multi-level atom calculations by more than 5 orders of magnitude. The
resulting code is fast enough for inclusion in Markov Chain Monte Carlo
parameter estimation algorithms. It does not yet include the radiative transfer
or high-n two-photon processes considered in some recent papers. Further work
on analytic treatments for these effects will be required in order to produce a
recombination code usable for Planck data analysis.Comment: Version accepted by Phys. Rev. D. Proof of equivalence of effective
and standard MLA methods moved to the main text. Some rewording
Ultrafast effective multi-level atom method for primordial hydrogen recombination
Cosmological hydrogen recombination has recently been the subject of renewed
attention because of its importance for predicting the power spectrum of cosmic
microwave background anisotropies. It has become clear that it is necessary to
account for a large number n >~ 100 of energy shells of the hydrogen atom,
separately following the angular momentum substates in order to obtain
sufficiently accurate recombination histories. However, the multi-level atom
codes that follow the populations of all these levels are computationally
expensive, limiting recent analyses to only a few points in parameter space. In
this paper, we present a new method for solving the multi-level atom
recombination problem, which splits the problem into a computationally
expensive atomic physics component that is independent of the cosmology, and an
ultrafast cosmological evolution component. The atomic physics component
follows the network of bound-bound and bound-free transitions among excited
states and computes the resulting effective transition rates for the small set
of "interface" states radiatively connected to the ground state. The
cosmological evolution component only follows the populations of the interface
states. By pre-tabulating the effective rates, we can reduce the recurring cost
of multi-level atom calculations by more than 5 orders of magnitude. The
resulting code is fast enough for inclusion in Markov Chain Monte Carlo
parameter estimation algorithms. It does not yet include the radiative transfer
or high-n two-photon processes considered in some recent papers. Further work
on analytic treatments for these effects will be required in order to produce a
recombination code usable for Planck data analysis.Comment: Version accepted by Phys. Rev. D. Proof of equivalence of effective
and standard MLA methods moved to the main text. Some rewording
Landau-Ginzburg Vacua of String, M- and F-Theory at c=12
Theories in more than ten dimensions play an important role in understanding
nonperturbative aspects of string theory. Consistent compactifications of such
theories can be constructed via Calabi-Yau fourfolds. These models can be
analyzed particularly efficiently in the Landau-Ginzburg phase of the linear
sigma model, when available. In the present paper we focus on those sigma
models which have both a Landau-Ginzburg phase and a geometric phase described
by hypersurfaces in weighted projective five-space. We describe some of the
pertinent properties of these models, such as the cohomology, the connectivity
of the resulting moduli space, and mirror symmetry among the 1,100,055
configurations which we have constructed.Comment: LaTeX, 33 pages, 10 PostScript figures using epsfig and psfi
Topical treatment of peripheral neuropathic pain: applying the evidence
Patients with peripheral neuropathic pain (NP) may only achieve partial pain relief with currently recommended first-line oral treatments, which are also associated with systemic adverse events. Topical treatments are currently considered second- or third-line options, but a recent pharmacologic treatment algorithm has called for broader first-line use of these agents. This has highlighted a need to communicate the benefits associated with topical agents, in particular around the efficacy, targeted local action, and limited systemic availability resulting in minimal systemic adverse events and drug-drug interactions
- …