Diffusion of Ultra High Energy Protons in Galaxy Clusters and Secondary X and Gamma Ray Emissions

In this work we simulate the propagation of Ultra High Energy (UHE) protons in the magnetised intergalactic medium of Galaxy Clusters (GCs). Differently from previous works on the subject, we trace proton trajectories in configurations of the Intra Cluster Magnetic Field (ICMF) which have been extracted from a constrained Magnetic-SPH simulation of the local universe. Such an approach allows us to take into account the effects of several features of the ICMFs, e.g. irregular geometrical structure and field fluctuations due to merger shocks,which cannot be investigated analitically or with usual numerical simulations. Furthermore, we are able to simulate a set of clusters which have properties quite similar to those of GCs observed in the nearby universe. We estimate the time that UHE protons take to get out of the clusters and found that in the energy range 5\times 10^{18} \simleq E \simleq 3 \times 10^{19} \eV proton propagation takes place in the Bohm scattering diffusion regime passing smoothly to a small pitch angle diffusion regime at larger energies. We apply our results to estimate the secondary gamma and Hard X Ray (HXR) emissions produced by UHE protons in a rich GC. We show that the main emission channel is due to the synchrotron HXR radiation of secondary electrons originated by proton photo-pair production scattering onto the CMB. This process may give rise to a detectable signal if a relatively powerful AGN, or a dead quasar, accelerating protons at UHEs is harboured by a rich GC in the local universe.Comment: 27 pages, 13 figure

Subtraction method in the second random--phase approximation: first applications with a Skyrme energy functional

We make use of a subtraction procedure, introduced to overcome double--counting problems in beyond--mean--field theories, in the second random--phase--approximation (SRPA) for the first time. This procedure guarantees the stability of SRPA (so that all excitation energies are real). We show that the method fits perfectly into nuclear density--functional theory. We illustrate applications to the monopole and quadrupole response and to low--lying $0^+$ and $2^+$ states in the nucleus $^{16}$O. We show that the subtraction procedure leads to: (i) results that are weakly cutoff dependent; (ii) a considerable reduction of the SRPA downwards shift with respect to the random--phase approximation (RPA) spectra (systematically found in all previous applications). This implementation of the SRPA model will allow a reliable analysis of the effects of 2 particle--2 hole configurations ($2p2h$) on the excitation spectra of medium--mass and heavy nuclei.Comment: 1 tex, 16 figure

Phase Diagrams of Forced Magnetic Reconnection in Taylor's Model

Recent progress in the understanding of how externally driven magnetic reconnection evolves is organized in terms of parameter space diagrams. These diagrams are constructed using four pivotal dimensionless parameters: the Lundquist number $S$, the magnetic Prandtl number $P_m$, the amplitude of the boundary perturbation $\hat \Psi_0$, and the perturbation wave number $\hat k$. This new representation highlights the parameters regions of a given system in which the magnetic reconnection process is expected to be distinguished by a specific evolution. Contrary to previously proposed phase diagrams, the diagrams introduced here take into account the dynamical evolution of the reconnection process and are able to predict slow or fast reconnection regimes for the same values of $S$ and $P_m$, depending on the parameters that characterize the external drive, never considered so far. These features are important to understand the onset and evolution of magnetic reconnection in diverse physical systemsComment: Comments: 13 pages, 2015 Workshop "Complex plasma phenomena in the laboratory and in the universe

A Lee-Yang--inspired functional with a density--dependent neutron-neutron scattering length

Inspired by the low--density Lee-Yang expansion for the energy of a dilute Fermi gas of density $\rho$ and momentum $k_F$, we introduce here a Skyrme--type functional that contains only $s$-wave terms and provides, at the mean--field level, (i) a satisfactory equation of state for neutron matter from extremely low densities up to densities close to the equilibrium point, and (ii) a good--quality equation of state for symmetric matter at density scales around the saturation point. This is achieved by using a density--dependent neutron-neutron scattering length $a(\rho$) which satisfies the low--density limit (for Fermi momenta going to zero) and has a density dependence tuned in such a way that the low--density constraint $|a(\rho) k_F| \le 1$ is satisfied at all density scales.Comment: 5 figure

The Sphaleron in a Magnetic Field and Electroweak Baryogenesis

The presence of a primordial magnetic field in the early universe affects the dynamic of the electroweak phase transition enhancing its strength. This effect may enlarge the window for electroweak baryogenesis in the minimal supersymmetric extension of the standard model or even resurrect the electroweak baryogenesis scenario in the standard model. We compute the sphaleron energy in the background of the magnetic field and show that, due to the sphaleron dipole moment, the barrier between topologically inequivalent vacua is lowered. Therefore, the preservation of the baryon asymmetry calls for a much stronger phase transition than required in the absence of a magnetic field. We show that this effect overwhelms the gain in the phase transition strength, and conclude that magnetic fields do not help electroweak baryogenesis.Comment: 10 pages, 2 figure

Pair-transfer probability in open- and closed-shell Sn isotopes

Approximations made to estimate two-nucleon transfer probabilities in ground-state to ground-state transitions and physical interpretation of these probabilities are discussed. Probabilities are often calculated by approximating both ground states, of the initial nucleus A and of the final nucleus A\pm 2 by the same quasiparticle vacuum. We analyze two improvements of this approach. First, the effect of using two different ground states with average numbers of particles A and A\pm2 is quantified. Second, by using projection techniques, the role of particle number restoration is analyzed. Our analysis shows that the improved treatment plays a role close to magicity, leading to an enhancement of the pair-transfer probability. In mid-shell regions, part of the error made by approximating the initial and final ground states by a single vacuum is compensated by projecting onto good particle number. Surface effects are analyzed by using pairing interactions with a different volume-to-surface mixing. Finally, a simple expression of the pair-transfer probability is given in terms of occupation probabilities in the canonical basis. We show that, in the canonical basis formulation, surface effects which are visible in the transfer probability are related to the fragmentation of single-particle occupancies close to the Fermi energy. This provides a complementary interpretation with respect to the standard quasiparticle representation where surface effects are generated by the integrated radial profiles of the contributing wave functions.Comment: 12 pages, 7 figure

Observation of explosive collisionless reconnection in 3D nonlinear gyrofluid simulations

The nonlinear dynamics of collisionless reconnecting modes is investigated, in the framework of a three-dimensional gyrofluid model. This is the relevant regime of high-temperature plasmas, where reconnection is made possible by electron inertia and has higher growth rates than resistive reconnection. The presence of a strong guide field is assumed, in a background slab model, with Dirichlet boundary conditions in the direction of nonuniformity. Values of ion sound gyro-radius and electron collisionless skin depth much smaller than the current layer width are considered. Strong acceleration of growth is found at the onset to nonlinearity, while at all times the energy functional is well conserved. Nonlinear growth rates more than one order of magnitude higher than linear growth rates are observed when entering into the small-$\Delta'$ regime

Hard Cosmic Ray Sea in the Galactic Center: a consistent interpretation of H.E.S.S. and Fermi-LAT γ\gamma-ray data

We present a novel interpretation of the gamma-ray diffuse emission measured by H.E.S.S. in the Galactic Center (GC) region and the Galactic ridge. Our starting base is an updated analysis of PASS8 Fermi-LAT data, which allows to extend down to few GeV the spectra measured by H.E.S.S. and to infer the primary CR radial distribution above 100 GeV. We compare those results with a CR transport model assuming a harder scaling of the diffusion coefficient with rigidity in the inner Galaxy. Such a behavior reproduces the radial dependence of the CR spectral index recently inferred from Fermi-LAT measurements in the inner GP. We find that, in this scenario, the bulk of the Galactic ridge emission can be naturally explained by the interaction of the diffuse, steady-state Galactic CR sea interacting with the gas present in the Central molecular zone. The evidence of a GC PeVatron is significantly weaker than that inferred adopting a conventional (softer) CR sea.Comment: Oral contribution to the International Cosmic Ray Conference (ICRC 2017), 12-20 July 2017, Bexco, Busan, Kore

Towards an expanded model of litigation

Introduction: The call for contributions for this workshop describes the important new challenges for the legal search community this domain brings. Rather than just understanding the challenges this domain poses in terms of their technical properties, we would like to suggest that understanding these challenges as socio-technical challenges will be important. That is, as well as calling for research on a technical level to address these challenges we are also calling for work to understand the social practices of those involved in e-discovery (ED) and related legal work. A particularly interesting feature of this field is that it is likely that search technologies will (at least semi-)automate responsiveness review in the relatively near term and this will change the way that the work is organised and done in many ways – offering new possibilities for new ways of organising the work. As well as designing those technologies for automating responsiveness review we need to be envisioning how the work will be done in the future, how these technologies will impact the organisation of the case and so on. In this position paper we therefore outline the importance of understanding the wider social context of ED when designing tools and technologies to support and change the work. We would like to reinforce and expand on Conrad’s call for IR researchers to understand just what ED entails [2], include the stages that come both before and after core retrieval activities. The importance of considering the social aspects of work in the design of the technology has been established for some time. Ushering in this ‘turn to the social,’ and focusing on interface design, Gentner and Grudin [4] described how the GUI has already changed from an interface for engineers, representing the engineering model of the machine to one that supported single ‘everyman’ users (based on ideas from psychology). From then onwards the interface has evolved to support groups of users, taking into account the social and organisational contexts of use. This has particular resonance for the design of ED technologies: during ED in particular and the wider legal process there are often many lawyers involved – reviewing documents, determining issues, etc. Even if the way that their work is organised currently is not seen as collaborative in the traditional sense – with individual lawyers working on individual document sets to review them - their work needs to be coordinated and it seems likely that their work could be enhanced by, for example, knowledge of what their colleagues had found, how the case was shaping up, new key terms and facts turned up and so on. Work is often modelled for the purposes of design using process models, but this misses out on the richness and variety actually found when one examines how the work is carried out [3]. Technologies which strictly enforce the process models can often hinder the work, or end up being worked around as was the case with workflow systems since people interpret processes very flexibly to get the work done ([1], [3]). Other studies in other fields have found similar problems when systems are designed on for example cognitive models of how the work is done; they often do not take into account the situated nature of the work and thus they can be very difficult to use [5]. We believe, like [2], that a clear understanding of the social practices of ED is vital for the creation of high-quality, meaningful tools and technologies. We furthermore propose that work practice studies, to be used in combination with other methods, are a central part of getting the detailed understanding of the work practices central to designing useful and intelligent tools. Work practice studies would involve ethnographies, consisting primarily of observation, undertaken of practitioners engaging in the work of ED