Petawatt laser absorption bounded

The interaction of petawatt ($10^{15}\ \mathrm{W}$) lasers with solid matter forms the basis for advanced scientific applications such as table-top particle accelerators, ultrafast imaging systems and laser fusion. Key metrics for these applications relate to absorption, yet conditions in this regime are so nonlinear that it is often impossible to know the fraction of absorbed light $f$, and even the range of $f$ is unknown. Here using a relativistic Rankine-Hugoniot-like analysis, we show for the first time that $f$ exhibits a theoretical maximum and minimum. These bounds constrain nonlinear absorption mechanisms across the petawatt regime, forbidding high absorption values at low laser power and low absorption values at high laser power. For applications needing to circumvent the absorption bounds, these results will accelerate a shift from solid targets, towards structured and multilayer targets, and lead the development of new materials

Absence of long-range chemical ordering in equimolar FeCoCrNi

Equimolar FeCoCrNi alloys have been the topic of recent research as "high-entropy alloys," where the name is derived from the high configurational entropy of mixing for a random solid solution. Despite their name, no systematic study of ordering in this alloy system has been performed to date. Here, we present results from anomalous x-ray scattering and neutron scattering on quenched and annealed samples. An alloy of FeNi_3 was prepared in the same manner to act as a control. Evidence of long-range chemical ordering is clearly observed in the annealed FeNi_3 sample from both experimental techniques. The FeCoCrNi sample given the same heat treatment lacks long-range chemical order

A search for stable strange quark matter nuggets in helium

A search for stable strange quark nuggets has been conducted in helium and argon using a high sensitivity mass spectrometer. The search was guided by a mass formula for strange quark nuggets which suggested that stable strange helium might exist at a mass around 65 u. The chemical similarity of such ``strangelets'' to noble gas atoms and the gravitational unboundedness of normal helium result in a large enhancement in the sensitivity of such a search. An abundance limit of no more than $2 \cdot 10^{-11}$ strangelets per normal nucleus is imposed by our search over a mass region from 42 to 82 u, with much more stringent limits at most (non-integer) masses.Comment: 11 pages RevTeX, Accepted for publication in Physics Letters B. 2 updated references added. Air abundance to cosmic abundance ratios now reflect updated references. No change in results or figures. Also see ftp://www-physics.mps.ohio-state.edu/pub/nucex/sq

Artificial Neural Network to predict mean monthly total ozone in Arosa, Switzerland

Present study deals with the mean monthly total ozone time series over Arosa, Switzerland. The study period is 1932-1971. First of all, the total ozone time series has been identified as a complex system and then Artificial Neural Networks models in the form of Multilayer Perceptron with back propagation learning have been developed. The models are Single-hidden-layer and Two-hidden-layer Perceptrons with sigmoid activation function. After sequential learning with learning rate 0.9 the peak total ozone period (February-May) concentrations of mean monthly total ozone have been predicted by the two neural net models. After training and validation, both of the models are found skillful. But, Two-hidden-layer Perceptron is found to be more adroit in predicting the mean monthly total ozone concentrations over the aforesaid period.Comment: 22 pages, 14 figure

Electromagnetic energy penetration in the self-induced transparency regime of relativistic laser-plasma interactions

Two scenarios for the penetration of relativistically intense laser radiation into an overdense plasma, accessible by self-induced transparency, are presented. For supercritical densities less than 1.5 times the critical one, penetration of laser energy occurs by soliton-like structures moving into the plasma. At higher background densities laser light penetrates over a finite length only, that increases with the incident intensity. In this regime plasma-field structures represent alternating electron layers separated by about half a wavelength by depleted regions.Comment: 9 pages, 4 figures, submitted for publication to PR

Setting limits on Effective Field Theories: the case of Dark Matter

The usage of Effective Field Theories (EFT) for LHC new physics searches is receiving increasing attention. It is thus important to clarify all the aspects related with the applicability of the EFT formalism in the LHC environment, where the large available energy can produce reactions that overcome the maximal range of validity, i.e. the cutoff, of the theory. We show that this does forbid to set rigorous limits on the EFT parameter space through a modified version of the ordinary binned likelihood hypothesis test, which we design and validate. Our limit-setting strategy can be carried on in its full-fledged form by the LHC experimental collaborations, or performed externally to the collaborations, through the Simplified Likelihood approach, by relying on certain approximations. We apply it to the recent CMS mono-jet analysis and derive limits on a Dark Matter (DM) EFT model. DM is selected as a case study because the limited reach on the DM production EFT Wilson coefficient and the structure of the theory suggests that the cutoff might be dangerously low, well within the LHC reach. However our strategy can also be applied to EFT's parametrising the indirect effects of heavy new physics in the Electroweak and Higgs sectors

Charged multifluids in general relativity

The exact 1+3 covariant dynamical fluid equations for a multi-component plasma, together with Maxwell's equations are presented in such a way as to make them suitable for a gauge-invariant analysis of linear density and velocity perturbations of the Friedmann-Robertson-Walker model. In the case where the matter is described by a two component plasma where thermal effects are neglected, a mode representing high-frequency plasma oscillations is found in addition to the standard growing and decaying gravitational instability picture. Further applications of these equations are also discussed.Comment: 14 pages (example added), to appear in Class. Quantum Gra

Multi-level Dynamical Systems: Connecting the Ruelle Response Theory and the Mori-Zwanzig Approach

In this paper we consider the problem of deriving approximate autonomous dynamics for a number of variables of a dynamical system, which are weakly coupled to the remaining variables. In a previous paper we have used the Ruelle response theory on such a weakly coupled system to construct a surrogate dynamics, such that the expectation value of any observable agrees, up to second order in the coupling strength, to its expectation evaluated on the full dynamics. We show here that such surrogate dynamics agree up to second order to an expansion of the Mori-Zwanzig projected dynamics. This implies that the parametrizations of unresolved processes suited for prediction and for the representation of long term statistical properties are closely related, if one takes into account, in addition to the widely adopted stochastic forcing, the often neglected memory effects.Comment: 14 pages, 1 figur

Surface Oscillations in Overdense Plasmas Irradiated by Ultrashort Laser Pulses

The generation of electron surface oscillations in overdense plasmas irradiated at normal incidence by an intense laser pulse is investigated. Two-dimensional (2D) particle-in-cell simulations show a transition from a planar, electrostatic oscillation at $2\omega$, with $\omega$ the laser frequency, to a 2D electromagnetic oscillation at frequency $\omega$ and wavevector $k>\omega/c$. A new electron parametric instability, involving the decay of a 1D electrostatic oscillation into two surface waves, is introduced to explain the basic features of the 2D oscillations. This effect leads to the rippling of the plasma surface within a few laser cycles, and is likely to have a strong impact on laser interaction with solid targets.Comment: 9 pages (LaTeX, Revtex4), 4 GIF color figures, accepted for publication in Phys. Rev. Let