528 research outputs found
Fingerprint Policy Optimisation for Robust Reinforcement Learning
Policy gradient methods ignore the potential value of adjusting environment
variables: unobservable state features that are randomly determined by the
environment in a physical setting, but are controllable in a simulator. This
can lead to slow learning, or convergence to suboptimal policies, if the
environment variable has a large impact on the transition dynamics. In this
paper, we present fingerprint policy optimisation (FPO), which finds a policy
that is optimal in expectation across the distribution of environment
variables. The central idea is to use Bayesian optimisation (BO) to actively
select the distribution of the environment variable that maximises the
improvement generated by each iteration of the policy gradient method. To make
this BO practical, we contribute two easy-to-compute low-dimensional
fingerprints of the current policy. Our experiments show that FPO can
efficiently learn policies that are robust to significant rare events, which
are unlikely to be observable under random sampling, but are key to learning
good policies.Comment: ICML 201
Constraints on Dark Matter-Neutrino Interaction from 21-cm Cosmology and Forecasts on SKA1-Low
In this article, we have done a thorough investigation of the possible
effects of interaction between dark matter (DM) and neutrinos on reionization
history. We have constrained the interaction strength using 21 cm Cosmology and
found out possible deviations from standard, non-interacting CDM
scenario. Comparing the results with the existing constraints from present
cosmological observations reveals that 21 cm observations are more competent to
constrain the interaction strength by a few orders of magnitude. We have also
searched for prospects of detecting any such interaction in the upcoming 21 cm
mission SKA1-Low by doing a forecast analysis and error estimation.Comment: Version considerably modified. To appear in MNRA
Performance Studies of Bulk Micromegas of Different Design Parameters
The present work involves the comparison of various bulk Micromegas detectors
having different design parameters. Six detectors with amplification gaps of
and mesh hole pitch of were tested at room temperature and normal gas pressure. Two
setups were built to evaluate the effect of the variation of the amplification
gap and mesh hole pitch on different detector characteristics. The gain, energy
resolution and electron transmission of these Micromegas detectors were
measured in Argon-Isobutane (90:10) gas mixture while the measurements of the
ion backflow were carried out in P10 gas. These measured characteristics have
been compared in detail to the numerical simulations using the Garfield
framework that combines packages such as neBEM, Magboltz and Heed.Comment: arXiv admin note: text overlap with arXiv:1605.0289
Near-inflection point inflation and production of dark matter during reheating
We study slow roll single field inflationary scenario and the production of
non-thermal fermionic dark matter, together with standard model Higgs, during
reheating. For the inflationary scenario, we have considered two models of
polynomial potential - one is symmetric about the origin and another one is
not. We fix the coefficients of the potential from the current Cosmic Microwave
Background (CMB) data from Planck/Bicep. Next, we explore the allowed parameter
space on the coupling with inflaton and mass of dark
matter (DM) particles produced during reheating and satisfying CMB and
several other cosmological constraints.Comment: Prepared for Proceedings of XXV Bled Workshop "What comes beyond the
Standard models?
Experimental and numerical simulation of a TPC like set up for the measurement of ion backflow
Ion backflow is one of the effects limiting the operation of a gaseous
detector at high flux, by giving rise to space charge which perturbs the
electric field. The natural ability of bulk Micromegas to suppress ion feedback
is very effective and can help the TPC drift volume to remain relatively free
of space charge build-up. An efficient and precise measurement of the backflow
fraction is necessary to cope up with the track distortion due to the space
charge effect. In a subtle but significant modification of the usual approach,
we have made use of two drift meshes in order to measure the ion backflow
fraction for bulk Micromegas detector. This helps to truly represent the
backflow fraction for a TPC. Moreover, attempt is taken to optimize the field
configuration between the drift meshes. In conjunction with the experimental
measurement, Garfield simulation framework has been used to simulate the
related physics processes numerically
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