12,184 research outputs found
Primordial Non-Gaussianity from LAMOST Surveys
The primordial non-Gaussianity (PNG) in matter density perturbation is a very
powerful probe of the physics of the very early Universe. The local PNG can
induce a distinct scale-dependent bias on the large scale structure
distribution of galaxies and quasars, which could be used for constraining it.
We study the detection limits on PNG from the surveys of the LAMOST telescope.
The cases of the main galaxy survey, the luminous red galaxy (LRG) survey, and
the quasar survey of different magnitude limits are considered. We find that
the MAIN1 sample (i.e. the main galaxy survey with one magnitude deeper than
the SDSS main galaxy survey, or r<18.8) could only provide very weak constraint
on PNG. For the MAIN2 sample (r<19.8) and the LRG survey, the 2\sigma (95.5%)
limit on the PNG parameter f_{NL} are |f_{NL}|<145 and |f_{NL}|<114
respectively, comparable to the current limit from cosmic microwave background
(CMB) data. The quasar survey could provide much more stringent constraint, and
we find that the 2\sigma limit for |f_{NL}| is between 50 and 103, depending on
the magnitude limit of the survey. With Planck-like priors on cosmological
parameters, the quasar survey with g<21.65 would improve the constraints to
|f_{NL}|<43 (2\sigma). We also discuss the possibility of further tightening
the constraint by using the relative bias method proposed by Seljak(2008).Comment: 8 pages, 2 figures, RAA accepte
Direct laser acceleration of electrons assisted by strong laser-driven azimuthal plasma magnetic fields.
A high-intensity laser beam propagating through a dense plasma drives a strong current that robustly sustains a strong quasistatic azimuthal magnetic field. The laser field efficiently accelerates electrons in such a field that confines the transverse motion and deflects the electrons in the forward direction. Its advantage is a threshold rather than resonant behavior, accelerating electrons to high energies for sufficiently strong laser-driven currents. We study the electron dynamics via a test-electron model, specifically deriving the corresponding critical current density. We confirm the model's predictions by numerical simulations, indicating energy gains two orders of magnitude higher than achievable without the magnetic field
Sensitive frequency-dependence of the carrier-envelope phase effect on bound-bound transition: an interference perspective
We investigate numerically with Hylleraas coordinates the frequency
dependence of the carrier-envelope phase (CEP) effect on bound-bound
transitions of helium induced by an ultrashort laser pulse of few cycles. We
find that the CEP effect is very sensitive to the carrier frequency of the
laser pulse, occurring regularly even at far-off resonance frequencies. By
analyzing a two-level model, we find that the CEP effect can be attributed to
the quantum interference between neighboring multi-photon transition pathways,
which is made possible by the broadened spectrum of the ultrashort laser pulse.
A general picture is developed along this line to understand the sensitivity of
the CEP effect to laser's carrier frequency. Multi-level influence on the CEP
effect is also discussed
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