448 research outputs found
Must Cosmological Perturbations Remain Non-Adiabatic After Multi-Field Inflation?
Even if non-adiabatic perturbations are generated in multi-field inflation,
the perturbations will become adiabatic if the universe after inflation enters
an era of local thermal equilibrium, with no non-zero conserved quantities, and
will remain adiabatic as long as the wavelength is outside the horizon, even
when local thermal equilibrium no longer applies. Small initial non-adiabatic
perturbations associated with imperfect local thermal equilibrium remain small
when baryons are created from out-of-equilibrium decay of massive particles, or
when dark matter particles go out of local thermal equilibrium.Comment: 12 pages, typographical errors corrected, acknowledgment added.
Article accepted for publication in Physical Review
How fast is the wave function collapse?
Using complex quantum Hamilton-Jacobi formulation, a new kind of non-linear
equations is proposed that have almost classical structure and extend the
Schroedinger equation to describe the collapse of the wave function as a
finite-time process. Experimental bounds on the collapse time are reported (of
order 0.1 ms to 0.1 ps) and its convenient dimensionless measure is introduced.
This parameter helps to identify the areas where sensitive probes of the
possible collapse dynamics can be done. Examples are experiments with
Bose-Einstein condensates, ultracold neutrons or ultrafast optics.Comment: 9 pages; v2: a shorter version to suit the 4 page limit of
Proceedings of International Conference on Mathematical Modelling in Physical
Sciences, 3-7 September 2012, Budapest, Hungary (IC-MSQUARE 2012
Effect of annealing on the hyperfine interaction in InAs/GaAs quantum dots
The hyperfine interaction of an electron with nuclei in the annealed
self-assembled InAs/GaAs quantum dots is theoretically analyzed. For this
purpose, the annealing process, and energy structure of the quantum dots are
numerically modeled. The modeling is verified by comparison of the calculated
optical transitions and of the experimental data on photoluminescence for set
of the annealed quantum dots. The localization volume of the electron in the
ground state and the partial contributions of In, Ga, and As nuclei to the
hyperfine interaction are calculated as functions of the annealing temperature.
It is established that the contribution of indium nuclei into the hyperfine
interaction becomes predominant up to high annealing temperatures (T = 980 C)
when the In content in the quantum dots does not exceed 25%. Effect of the
nuclear spin fluctuations on the electron spin polarization is numerically
modeled. Effective field of the fluctuations is found to be in good agreement
with experimental data available
Neutrino statistics and big bang nucleosynthesis
Neutrinos may possibly violate the spin-statistics theorem, and hence obey
Bose statistics or mixed statistics despite having spin half. We find the
generalized equilibrium distribution function of neutrinos which depends on a
single fermi-bose parameter, \kappa, and interpolates continuously between the
bosonic and fermionic distributions when \kappa changes from -1 to +1. We
consider modification of the Big Bang Nucleosynthesis (BBN) in the presence of
bosonic or partly bosonic neutrinos. For pure bosonic neutrinos the abundances
change (in comparison with the usual Fermi-Dirac case) by -3.2% for 4He (which
is equivalent to a decrease of the effective number of neutrinos by \Delta
N_\nu = - 0.6), +2.6% for 2H and -7% for 7Li. These changes provide a better
fit to the BBN data. Future BBN studies will be able to constrain the
fermi-bose parameter to \kappa > 0.5, if no deviation from fermionic nature of
neutrinos is found. We also evaluate the sensitivity of future CMB and LSS
observations to the fermi-bose parameter.Comment: 11 pages, 3 figures, matches version in JCAP, discussion and
references extended slightl
Spin flip from dark to bright states in InP quantum dots
We report measurements of the time for spin flip from dark (non-light
emitting) exciton states in quantum dots to bright (light emitting) exciton
states in InP quantum dots. Dark excitons are created by two-photon excitation
by an ultrafast laser. The time for spin flip between dark and bright states is
found to be approximately 200 ps, independent of density and temperature below
70 K. This is much shorter than observed in other quantum dot systems. The rate
of decay of the luminescence intensity, approximately 300 ps, is not simply
equal to the radiative decay rate from the bright states, because the rate of
decay is limited by the rate of conversion from dark excitons into bright
excitons. The dependence of the luminescence decay time on the spin flip time
is a general effect that applies to many experiments.Comment: 3 figure
Experimental implications of mirror matter-type dark matter
Mirror matter-type dark matter is one dark matter candidate which is
particularly well motivated from high energy physics. The theoretical
motivation and experimental evidence are pedagogically reviewed, with emphasis
on the implications of recent orthopositronium experiments, the DAMA/NaI dark
matter search, anomalous meteorite events etc.Comment: about 12 pages lon
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