118851022
Kinetics of Particles in Relativistic Collisionless Shocks
Charged plasma particles form an anisotropic counter-streaming distribution at the front of a shock. In the nearand ultra-relativistic regimes, Weibel (or twostream) instability produces near-equipartition, chaotic, small-scale magnetic fields. The fields introduce effective collisions and “thermalize” the plasma particles via pitch-angle scattering. The properties of jitter radiation emitted by accelerated electrons from these small-scale fields are markedly different from synchrotron spectra. Here we theoretical summary and the results of recent numerical 3D PIC plasma kinetic simulations. The relation of the obtained results to the theory of gamma-ray bursts is outlined.
121799036
Modeling of laser wakefield acceleration in the Lorentz boosted frame using OSIRIS and UPIC framework
We examine numerical issues related to modeling laser wakefield acceleration (LWFA) in a Lorentz boosted frame. We present some theoretical results on a numerical instability that results from a relativistic plasma drift on a grid. We compare these predictions with results obtained from a finite difference time domain (FDTD) code OSIRIS and a spectral (FFT) time domain code UPIC. Consistent with the theoretical predictions, it is found that the spectral solver has advantages for mitigating the numerical instability when compared against some prevailing (FDTD) solvers. We also compared using finite difference or spectral field solvers in simplified 2D LWFA simulations using a plane wave for the laser. We find that the use of the spectral solver has advantages for mitigating the numerical instability induced by the relativistically drifting plasma.
1541538
Weibel-instability-mediated collisionless shocks in the laboratory with ultraintense lasers.
The formation of nonrelativistic collisionless shocks in the laboratory with ultrahigh intensity lasers is studied via ab initio multidimensional particle-in-cell simulations. The microphysics behind shock formation and dissipation and the detailed shock structure are analyzed, illustrating that the Weibel instability plays a crucial role in the generation of strong subequipartition magnetic fields that isotropize the incoming flow and lead to the formation of a collisionless shock, similar to what occurs in astrophysical scenarios. The possibility of generating such collisionless shocks in the laboratory opens the way to the direct study of the physics associated with astrophysical shocks.
28592387
Ion motion in self-modulated plasma wakefield accelerators.
The effects of plasma ion motion in self-modulated plasma-based accelerators are examined. An analytical model describing ion motion in the narrow beam limit is developed and confirmed through multidimensional particle-in-cell simulations. It is shown that the ion motion can lead to the early saturation of the self-modulation instability and to the suppression of the accelerating gradients. This can reduce the total energy that can be transformed into kinetic energy of accelerated particles. For the parameters of future proton-driven plasma accelerator experiments, the ion dynamics can have a strong impact. Possible methods to mitigate the effects of the ion motion in future experiments are demonstrated.
118588748
Electron-scale shear instabilities: magnetic field generation and particle acceleration in astrophysical jets
Strong shear flow regions found in astrophysical jets are shown to be important dissipation regions, where the shear flow kinetic energy flow is converted into electric and magnetic field energy via shear instabilities. The emergence of these self-consistent fields makes shear flows significant sites for radiation emission and particle acceleration. We focus on electron-scale instabilities, namely the collisionless, unmagnetized electron-scale Kelvin?Helmholtz instability (ESKHI) and a large-scale DC magnetic field generation mechanism on the electron scales. We show that these processes are important candidates to generate magnetic fields in the presence of strong velocity shears, which may naturally originate in energetic matter outbursts of active galactic nuclei and gamma-ray bursters. We show that the ESKHI is robust to density jumps between shearing flows, thus operating in various scenarios with different density contrasts. Multidimensional particle-in-cell (PIC) simulations of the ESKHI, performed with OSIRIS, reveal the emergence of a strong and large-scale DC magnetic field component, which is not captured by the standard linear fluid theory. This DC component arises from kinetic effects associated with the thermal expansion of electrons of one flow into the other across the shear layer, whilst ions remain unperturbed due to their inertia. The electron expansion forms DC current sheets, which induce a DC magnetic field. Our results indicate that most of the electromagnetic energy developed in the ESKHI is stored in the DC component, reaching values of equipartition on the order of 10?3 in the electron time-scale, and persists longer than the proton time-scale. Particle scattering/acceleration in the self-generated fields of these shear flow instabilities is also analyzed.
12875278
Near-GeV-energy laser-wakefield acceleration of self-injected electrons in a centimeter-scale plasma channel.
The first three-dimensional, particle-in-cell (PIC) simulations of laser-wakefield acceleration of self-injected electrons in a 0.84 cm long plasma channel are reported. The frequency evolution of the initially 50 fs (FWHM) long laser pulse by photon interaction with the wake followed by plasma dispersion enhances the wake which eventually leads to self-injection of electrons from the channel wall. This first bunch of electrons remains spatially highly localized. Its phase space rotation due to slippage with respect to the wake leads to a monoenergetic bunch of electrons with a central energy of 0.26 GeV after 0.55 cm propagation. At later times, spatial bunching of the laser enhances the acceleration of a second bunch of electrons to energies up to 0.84 GeV before the laser pulse intensity is significantly reduced.
118081166
Renormalization in supersymmetric models
There are reasons to believe that the Standard Model is only an effective theory, with new Physics lying beyond it. Supersymmetric extensions are one possibility: they address some of the Standard Model's shortcomings, such as the instability of the Higgs boson mass under radiative corrections. In this thesis, some topics related to the renormalization of supersymmetric models are analyzed. One of them is the automatic computation of the Lagrangian and the renormalization group equations of these models, which is a hard and error-prone process if carried out by hand. The generic renormalization group equations themselves are extended so as to include those models which have more than a single abelian gauge factor group. Such situations can occur in grand unified theories, for example. For a wide range of SO(10)-inspired supersymmetric models, we also show that the renormalization group imprints on sparticle masses some information on the higher energies behavior of the models. Finally, in some cases these theories introduce charged lepton flavor violating interactions, which can change the ratio $\Gamma\left(K\rightarrow e\nu\right)/\Gamma\left(K\rightarrow\mu\nu\right)$. In light of experimental bounds on other observables, our analysis shows that any change over the Standard Model prediction must be smaller than the current experimental sensitivity on this observable.
31040253
Calculating the renormalisation group equations of a SUSY model with Susyno
Susyno is a Mathematica package dedicated to the computation of the 2-loop renormalisation group equations of a supersymmetric model based on any gauge group (the only exception being multiple U(1) groups) and for any field content. Supersymmetry (SUSY) is an elegant and well known extension of the Standard Model (SM) which aims at solving or softening some of the SM theoretical and experimental shortcomings. Supersymmetric models based on Grand Unified Theories (GUTs) offer the appealing feature of being described by a unique gauge group and coupling constant; furthermore, the potential new superfields, as well as their dynamics, can provide answers to fundamental problems. For example SO(10) based models offer a natural explanation for neutrino masses and mixings via a type-I seesaw. This occurs since the spinor representation of the group contains a SM singlet superfield (with the appropriate quantum numbers). Even larger and/or more complex groups are often considered, for example E6 in string inspired models. The analysis of the theoretical and phenomenological implications of SUSY GUT models requires a careful study of the evolution of the fundamental parameters from the high-energy scale down to the electroweak scale, at which observables are computed and constraints applied. As such, knowledge of the renormalisation group equations (RGEs) is necessary. Although the RGEs of several models (e.g., MSSM, NMSSM) are already known [1, 3], for other SUSY extensions of the SM complicated general equations must be used [1, 2]. Here we describe Susyno, a Mathematica-based package that addresses this issue. The program takes as input the gauge group, the representations (i.e., the chiral superfield content), the number of flavours/copies 1 of each representation, and any abelian discrete symmetries (e.g., R-parity). Susyno then constructs the most general superpotential and soft SUSY breaking Lagrangian consistent with the field content and symmetries imposed. Once these elements have been derived, Susyno then computes the 2-loop �-functions of all the parameters of the model, which is its main output.
118698479
Supersymmetric SO(10)-inspired GUTs with sliding scales
This work has been supported in part by EU Network Grant No. UNILHC PITN-GA-2009-237920. M. H. also acknowledges support from the Spanish MICINN Grants No. FPA2011-22975, No. MULTIDARK CSD2009-00064 and by the Generalitat Valenciana Grant No. Prometeo/2009/091. The work of R. M. F has been supported by Fundacao para a Ciencia e a Tecnologia through the fellowship SFRH/BD/47795/2008. R. M. F. and J. C. R. also acknowledge the financial support from Grants No. CFTP-FCT UNIT 777, No. CERN/FP/123580/2011 and No. PTDC/FIS/102120/2008.
118530599
Running soft parameters in SUSY models with multiple U(1) gauge factors
Abstract We generalize the two-loop renormalization group equations for the parameters of the softly broken SUSY gauge theories given in the literature to the most general case when the gauge group contains more than a single Abelian gauge factor. The complete method is illustrated at two-loop within a specific example and compared to some of the previously proposed partial treatments.