A. G. Aksenov, R. Ruffini, G. V. Vereschagin
We consider the mass accretion $0.5M_\odot$ to the neutron star (NS) $1.4M_\odot$. We take into account main physical processes and neutrino transport in the spherical-symmetric model [1]. The calculation region includes NS and background uniform mass in the radius $10^9$cm. The results of calculations are new massive hot NS. Main part of the energy is escaped by neutrino. Part of the energy $10^{50}$ erg is released in kinetic energy of the ejected mass. We discuss the possibility of the application of calculations to GRB in the induced gravitational collapse of NS to a black hole [2].

[1] A. G. Aksenov, V. M. Chehetkin // Astr. Rep., 56, 193 (2012)
[2] J. A. Rueda, R. Ruffini // ApJL, 758, L7 (2012)

National Research Nuclear University MEPhI - Kashirskoe sh. 31, RU-115409 Moscow, Russia
Several thousands of gamma-ray bursts were observed by various experiments, but their sources origin still remains unclear up to now. During several GRBs very high-energy photons were detected both in space and ground-based experiments (up to some tens of GeV and up to some TeV, respectively). The shape of redshift distribution for uniform sources set in our Metagalaxy defined by cosmological parameters and properties of space is Euclidean at small redshifts and de-Stter at z>0.7. As example of real uniform set the shape of normalized z distributions for set of SNIa including objects which were used for definition of and for our Metagalaxy and for first 604 QSO from 2QZ_6QZ catalogue are analyzed. It is reveal that 5-9% events in dependence of amount of sampling must be in the tails of distributions above 3 levels for significant one-peak fit of uniform set with confidence level 95-97%. The investigation results of GRB with defined duration redshifts distribution from SWIFT registered subset (~260 events) and Fermi observed one (~100 bursts) discussed in the presented talk. The detailed studying has shown at least 2 maxima in both distributions. Even if only classic long GRB with duration >2s (without redshift correction) taking into account the same distribution structure retains. Moreover the GRB distribution on redshift and duration allow to conclude the presents of new subgroup should interpreted as intermediate GRB registered by BATSE experiment.
As a result, we show that the generated circular polarization can be experimentally measured by two head-on colliding optical laser beams of a cross-sectional area 0.01 cm^2 and a laser pulse energy of ∼mJ, which are currently available in laboratories. Our study presents a valuable supplement to other theoretical and experimental frameworks for the study and measurement of the non-linear effects of photon-photon interaction in quantum electrodynamics.

A.M. Galper(1)(2), R.L. Aptekar(3), I.V. Arkhangelskaja(2), A.I. Arkhangelskiy(2), Yu.V. Gusakov(1), M.D. Kheymits(2), A.A. Leonov(2), E.P. Mazets(3), M.F. Runtso(2), S.I. Suchkov(1), N.P. Topchiev(1), Yu.T. Yurkin(2), V.G. Zverev(2) on behalf of GAMMA-400 collaboration
(1) Lebedev Physical Institute, Russian Academy of Sciences - Leninskii pr. 53, RU-119991, Moscow, Russia;
(2) National Research Nuclear University MEPhI - Kashirskoe sh. 31, RU-115409 Moscow, Russia
(3) Ioffe Physical Technical Institute, Russian Academy of Sciences – ul. Polytekhnicheskaya 26, RU-194021 St. Petersburg, Russia
The GAMMA-400 future space experiment consists of the GAMMA-400 gamma-ray telescope to register gammas and electrons in the energy range of 100 MeV - 3 TeV, high energy nuclei and the KONUS-FG system to detect gamma-ray bursts in the range of 10 keV - 10 MeV similar to the KONUS/WIND instrument. The GAMMA-400 gamma-ray telescope will have the angular resolution of ~0.02 deg for E > 100 GeV, the energy resolution of ~ 2% for E > 10 GeV, time resolution of ~0.1 ms allow to investigate discrete sources, diffuse background and dark matter. The methods of on-board triggers and trigger markers formation are proposed.

ESA
The European Space Agency (ESA) has selected the gravitational universe as the theme of a large-class mission with a nominal launch date of 2034. The definition of feasibility and reduction of risks for a space-borne observatory are therefore mandatory. Timely, the lisa pathfinder spacecraft by esa is on schedule to fly by autumn 2015. Implementing a high precision free-fall in-flight system near a lagrangian point, the mission relies on technologies never used before in space environments and crucial to gravitational waves observatories. Lisa pathfinder shall collect data to project the best free-fall residual acceleration noise picture measured so far. I will describe the typical elisa-like observatory apparatus and show its qualities as gravitational signal instrument in the low frequency bandwidth, sketching the science it could do and that is unachievable on ground due to newtonian noise barriers. I shall also show why lisa pathfinder is a breakthrough of its own on the side of engineering and on that of space operations too.

The window is found in the space of the free parameters of the theory of viscoelastic matter for which the Friedmann singularity is stable. Under stability we mean that in the presence of the shear stresses the generic solution of the equations of relativistic gravity posessing the isotropic cosmological singularity exists.

E. Bittencourt, V. A. De lorenci, R. Klippert, M. Novello and J. M. Salim
Propagation of light in nonlinear materials is here studied in the regime of the geometrical optics. It is shown that a spherically symmetric medium at rest with some specific dielectric properties can be used to produce an exact analogue model for a class of space-times which includes spherically symmetric and static black hole solutions. The optical model here presented can be a useful tool to reproduce in laboratory the behavior of optical null geodesics near a compact object with an observable gravitational schwarzschild radius.

F. Canfora, A. Giacomini, S. Pavluchenko
In this talk, intriguing gravitational features of the skyrme lagrangian (whose importance is well known in nuclear and particles physics) will be described. The novel technical tool to disclose them, which is the generalized hedgehog ansatz for the skyrmion, will be described in details. Applications in black hole physics and cosmology will be shortly described.

Black hole accretion is necessarily transonic. Depending on the viscosity and cooling processes the flow may or may not assume keplerian, optically thick cool disk as described by standard shakura-sunyaev prescription. We show that for realistic heating and cooling, the generally has two components: one component is similar to a shakura-sunyaev disk, through still passing through the inner sonic point. The other component has lower angular momentum and surrounds the keplerian disk. This so-called halo component can have a strong centrifugal barrier dominated boundary layer known as cenbol. This cenbol behaves as a compton cloud and energizes soft seed photons from the keplerian disk. It generates outflows or jets. Its oscillation causes quasi-periodic oscillations of comptonized photons. We incorporate the nature of the companion and show that it plays a major role in determining the flow properties.

According to theoretical models, massive stars with masses within the 100–250 M range should explode as pair-instability supernovae (PISNe). Since the first stars of the Universe are believed to be very massive, these supernovae should play a significant role in the early stages of its history. But these stars represent the last unobserved population, owing to detection limits of current telescopes. In this work we analyze pair-instability supernovae explosions using various numerical codes. We evolve series of the configurations of oxygen cores to establish a range of masses and initial conditions where this type of explosion is possible. We also study the role of possible instabilities in the propagation of shockwaves during the last stage of the explosion. This investigation could help us to predict the observational properties of PISNe for future space and ground telescopes.

Massive, highly magnetized white dwarfs with fields up to $10^9$~G have been observed and theoretically used for the description of a variety of astrophysical phenomena. Ultramagnetized white dwarfs with uniform interior fields up to $10^{18}$~G, have been recently purported to obey a new maximum mass limit, $M_{\rm max}\approx 2.58~M_\odot$, which largely overcomes the traditional Chandrasekhar value, $M_{\rm Ch}\approx 1.44~M_\odot$. Such a much larger limit would make these astrophysical objects viable candidates for the explanation of the superluminous population of type Ia supernovae.
We show that several macro and micro physical aspects such as gravitational, dynamical stability, breaking of spherical symmetry, general relativity, inverse $\beta$-decay, and pycnonuclear fusion reactions are of most relevance for the self-consistent description of the structure and assessment of stability of these objects. It is shown in this work that the first family of magnetized white dwarfs indeed satisfy all the criteria of stability, while the ultramagnetized white dwarfs are very unlikely to exist in nature since they violate minimal requests of stability. Therefore, the canonical Chandrasekhar mass limit of white dwarfs has to be still applied.

Max-Planck-Institut für Kernphysik, Saupfercheckweg 1, D-69117 Heidelberg, Germany
Quantum electrodynamics (QED) is a well established theory and its predictions have been successfully confirmed experimentally in different regimes. However, there are still areas of QED that deserve theoretical and experimental investigation, especially when processes occur in the presence of electromagnetic background fields of the order of the so-called critical fields of QED [1]. Highly-charged ions, like lead or uranium, already provide electric fields of the order of the critical electric field of QED (∼ 1016 V/cm). In view of the increasingly stronger available laser fields it is becoming feasible also to employ them to test QED under the extreme conditions supplied by ultra-intense fields [1].
The interplay between the strong field provided by a highly-charged ion and by an ultra-intense laser beam has been investigated in the process of electron-positron photo-production (Bethe-Heitler process) [2]. Since in the presence of incoming photons with energies much larger than the electron rest energy, the laser field amplitude can be effectively boosted to the critical value in the center-of-momentum frame of the created pair. It has been shown that, unexpectedly, the presence of the laser field can strongly suppress the Bethe-Heitler cross section, an effect analogous to the Landau-Pomeranchuk-Migdal effect in crystals.
Finally, on a more experimental side, we have investigated the possibility of producing ultra-relativistic leptonic (positron and/or electron-positron) beams for strong-field QED experiments in an all-optical setup [3]. By generating an incoming monoenergetic electron beam via laser wake-field acceleration and by colliding it with a solid target, we succeeded in producing for the first time positron beams of short (∼ 30 fs) duration, with ultra-relativistic energies (> 100 MeV), and with a narrow angular distribution (∼ 3 mrad) in a table-top setup. The possibility of generating high-energy lepton beams in laboratory is also of central importance for astrophysics, due to their similarity to jets of long gamma-ray bursts.

[1] A. Di Piazza, C. Müller, K. Z. Hatsagortsyan, and C. H. Keitel, Rev. Mod. Phys. 84, 1177 (2012).
[2] A. Di Piazza and A. I. Milstein, Phys. Lett. B 717, 224 (2012); A. Di Piazza and A. I. Milstein, Phys. Rev. A (in press). See also http://arxiv.org/abs/1404.5732.
[3] G. Sarri, W. Schumaker, A. Di Piazza, M. Vargas, B. Dromey, M. E. Dieckmann, V. Chvykov, A. Maksimchuk, V. Yanovsky, Z. H. He, B. X. Hou, J. A. Nees, A. G. R. Thomas, C. H. Keitel, M. Zepf, and K. Krushelnick, Phys. Rev. Lett. 110, 255002 (2013).

F. Canfora, A. Giacomini, S. Pavluchenko
We study anisotropic cosmologies where the matter source is given by the skyrme model. More precisely dynamical evolution of the kantowski-sachs and the bianchi i universes are studied. In both situations, in order to have solutions and to avoid finite time future singularities, bounds on the value of the cosmological constants must be set. These bounds arise from coupling the skyrme model, which is an effective low energy qcd describing as well pions as baryons, to gravity in a regime where both theories are perfectly valid. This especially means it is possible to get a physical mechanism which restricts the value of the cosmological constant without any assumptions on quantum gravity.

K. Z. Hatsagortsyan, C. Müller, G. Yu. Kryuchkyan, A. Ipp, M. Ruf, G. R. Mocken, J. Evers,  N. Kumar, and C. H. Keitel
Superstrong laser fields are envisaged in the future european extreme light infrastructure which will allow to reach and test nonlinear qed and, in particular, the critical field phenomena in the rest frame of the relativistic particles accelerated in all-optical setups. We discuss several processes interesting also for astrophysics, new features in specific setups, and possible applications. In particular, production of electron-positron pairs from vacuum by counterpropagating laser beams is considered, where the role of the spatial dependence and magnetic component of the laser field are investigated. The latter strongly affects the creation process at high laser frequency: the production probability is reduced, the particle spectra are modified, the resonant rabi-oscillation pattern is distorted, and the resonance positions are shifted, multiplied, and split [1]. Employing the electron-positron pair production process, we propose a detection scheme for characterizing high-energy gamma-ray pulses in the super-mev energy range down to the zeptosecond timescale during the collision of a test pulse with an intense laser pulse [2]. At relatively low laser fields, we have shown how the coherence effects arising in spatially structured vacuum in strong periodic fields can enhance the vacuum polarization effects. The bragg scattering can be employed to detect the vacuum polarization effect in a setup of multiple crossed superstrong laser beams [3]. Finally, the effect of the radiation reaction in the stimulated raman scattering of an ultraintense laser pulse in plasmas is studied. The radiation reaction causes a phase shift in nonlinear current densities that drive the two raman sidebands (anti-stokes and stokes waves), manifesting itself into the nonlinear mixing of two sidebands. This mixing results in a strong enhancement in the growth of the forward raman scattering instability [4]. We consider also signatures of the quantum radiation reaction in multiphoton compton scattering [5].

[1] M. Ruf, G. R. Mocken, C. Müller, K. Z. Hatsagortsyan and C. H. Keitel, phys. Rev. Lett. 102, 080402 (2009).
[2] A. Ipp, J. Evers, C. H. Keitel, and K. Z. Hatsagortsyan, phys. Lett. B 702, 383 (2011).
[3] G. Yu. Kryuchkyan and K. Z. Hatsagortsyan, phys. Rev. Lett. 107, 053604 (2011).
[4] N. Kumar, K. Z. Hatsagortsyan, C. H. Keitel, phys. Rev. Lett. 111, 105001 (2013).
[5] Jian-Zing Li, K. Z. Hatsagortsyan, and C. H. Keitel, to be published.

At the onset of special and general relativity before the quantum nature of the electron was understood, many early physicists tried to relate the mass of the classical electron to the electromagnetic energy stored in its Coulomb field. Fermi had the most convincing approach at the most elementary level but the question has lingered ever since. The problem provides a nice pedagogical example of working with Gauss's law and Maxwell's equations in a spacetime setting, something few students have an opportunity to do.

C. H. Keitel, S. M. Cavaletto, J. Gunst, Z. Harman and A. Pálffy;
Max Planck Institute for Nuclear Physics (MPIK), Saupfercheckweg 1, 69117 Heidelberg, Germany, phone: ++49 (0)6221/516-151, fax: ++49 (0)6221/516-152; keitel@mpi-hd.mpg.de
The profound understanding of the interaction of highly charged ions and nuclei with x-ray photons is of seminal importance for many astrophysical scenarios. In recent years x-ray quantum optics with free-electron lasers and synchrotron light has been vastly progressing including outstanding fundamental advances [1] and direct applications in astrophysics [2], for reviews see [3]. In this talk, emphasis is placed on illuminating astrophysical spectra from iron ions via laboratory astrophysics with free-electron lasers [2] and on recent results in nuclear isomer triggering [4] and in developing broadband high-resolution x-ray frequency combs for possible high precision spectroscopy [5].

[1] R. Röhlsberger, H.-C. Wille, K. Schlage, and B. Sahoo, Nature 482, 199-203 (2012), K. P. Heeg, H. Wille, K. Schlage, T. Guryeva, D. Schumacher, I. Uschmann, K. S. Schulze, B. Marx, T. Kämpfer, G. G. Paulus, R. Röhlsberger, and J. Evers, Phys. Rev. Lett. 111, 073601 (2013), F. Vagizov, V. Antonov, Y. V. Radeonychev, R. N. Shakhmuratov, and O. Kocharovskaya, Nature 508, 80–83 (2014).
[2] S. Bernitt, G. V. Brown, J. K. Rudolph, R. Steinbrügge, A. Graf, M. Leutenegger, S. W. Epp, S. Eberle, K. Kubiček, V. Mäckel, M. C. Simon, E. Träbert, E. W. Magee, C. Beilmann, N. Hell, S. Schippers, A. Müller, S. M. Kahn, A. Surzhykov, Z. Harman, C. H. Keitel, J. Clementson, F. S. Porter, W. Schlotter, J. J. Turner, J. Ullrich, P. Beiersdorfer, and J. R. Crespo López-Urrutia, Nature 492, 225-228 (2012) and N. Oreshkina, C. H. Keitel and Z. Harman, to be submitted (2014).
[3] B. W. Adams, C. Buth, S. M. Cavaletto, J. Evers, Z. Harman, C. H. Keitel, A. Pálffy, A. Picon, R. Röhlsberger, Y. Rostovtsev, and K. Tamasaku, J. Mod. Opt. 60, 2 (2013), A. Di Piazza, C. Müller, K. Z. Hatsagortsyan, and C. H. Keitel, Rev. Mod. Phys. 84, 1177 (2012).
[4] J. Gunst, Y. A. Litvinov, C. H. Keitel, A. Pálffy, Phys. Rev. Lett. 112, 082501 (2014).
[5] S. M. Cavaletto, Z. Harman, C. Ott, C. Buth, T. Pfeifer, C. H. Keitel, accepted for publication in Nature Photonics (2014), arXiv:1402.6652.

High magnetic fields hinders our ability to measure the surface gravity from the spectral lines, their colors and certainly the internal pressure. There is indication that magnetic white dwarfs are more massive than the average, but it has been hard to determine how much.

J. Y. Kim, T. Lee
We consider the velocity shift of light in presence of radiation emitted by a black body. Within geometric optics formalism we calculate the bending angle of a light ray when there is a gradient in the energy density. We model the bending for two simplified cases. The bending angle is proportional to the inverse square power of the impact parameter ($\propto 1/b^2$) when the dilution of energy density is spherically symmetric. The bending angle is inversely proportional to the impact parameter ($\propto 1/b$) when the energy density dilutes cylindrically. Assuming that a neutron star is an isothermal black body, we estimate the order of magnitude for such bending angle and compare it with the bending angle by magnetic field.

We consider the the spacetime of a wormhole in frw (friedmann-robertson-walker) cosmological model. There are two horizons in the model: the apparent cosmological horizon and the wormhole trapping horizon. The hawking temperature near the horizons are calculated through the formula on the surface gravity and the wkb approximation for tunneling probability.

A. Stepanian, M. Kohandel
First the existence of different unitary inequivalent representations in the quantum field theory is discussed. Then it is shown that how they can play a major role for us to understand some phenomena such as hawking effect.

Gamma-ray burst (GRB) - short introduction;
Fermi-LAT observations of GRBs;
Light curves in the rest frame and in high energy band of GRBs with known redshift - methods of obtaining them;
Emitted energy of these GRBs in high energy band.

¹Institute of Physics, University of Oldenburg, Germany - E-mail: jutta.kunz@uni-oldenburg.de
First generalizations of the Kerr black holes are discussed which are obtained by including higher curvature corrections in the form of the Gauss-Bonnet density coupled to the dilaton [1]. The domain of existence of these Einstein-Gauss-Bonnet-dilaton (EGBd) black holes is bounded by the Kerr black holes, by the critical EGBd black holes, and by singular extremal EGBd solutions. The angular momentum of these EGBd black holes can slightly exceed the Kerr bound. For their innermost stable circular orbits the radius to mass ratio can deviate by 10% from the Kerr value.
Their orbital frequencies can deviate by 60%. This may lead to astrophysically observable effects.
Next rapidly rotating neutron stars in EGBd theory are discussed. Their physical properties are analyzed, including their moment of intertia and their quadrupole moment. Then universality relations are addressed.
Finally wormholes in EGBd theory are discussed. The presence of the Gauss-Bonnet term allows for radially stable wormholes without the need for exotic matter [2].

[1] B. Kleihaus, J. Kunz and E. Radu, Phys. Rev. Lett. 106, 151104 (2011)
[2] P. Kanti, B. Kleihaus and J. Kunz, Phys. Rev. Lett. 107, 271101 (2011)

C. Laemmerzahl, A. Garcia, E. Hackmann, J. Kunz, A. Macias
we consider the motion of test particles in the regular black hole space-time given by ayon-beato and garcia in phys. Rev. Lett. 80:5056 (1998). The complete set of orbits for neutral and weakly charged test particles is discussed, including for neutral particles the extreme and over-extreme metric. We also derive the analytical solutions for the equation of motion of neutral test particles in a parametric form and consider a post-schwarzschild expansion of the periastron shift to second order in the charge.

H. Won Lee, K. Yee. Kim
Recently dark energy is one of the most mystery remained to resolve or understand. Modern observational astrophysics confirms that the universe is accelerating expansion and there are many theoretical models to explain this late time expansion. However, there is no fundamental explanation for the origin of dark energy. The main purpose of this work is to find a possible physical explanation for the origin of dark energy. In the previous work, we showed that massive degenerate neutrino could explain the late time acceleration. In this work, we focused on the detailed study of quantum mechanical property for massive degnerate neutrino was performed to understand how fermionic energy could act as a cosmological constant at the late time evolution. Special attention was paid how the ferminoic property affect the energy density distribution.

S. Khodagholizadeh, R. Mohammadi, S. S. Xue

Formation of astrophysical black holes mediated by nonlinear electrodynamics theorists of the general theory of relativity contend that in nature there exists electrically charged black holes, celestial objects which a distant observer would characterize by their mass and charge. Notwithstanding, none astrophysical mechanism has been proved to self-consistently break up the universal global charge neutrality of most cosmic systems. Foundational arguments from nonlinear electrodynamics (nled) provide a mechanism able to drive the formation of an astrophysical charged black hole upon the gravitational collapse of a massive star. Due to its repulsive action (nonlinear exponential grow of the initial field in a rotating proto-neutron star (p-ns) caused by positive feedback to itself) nled allows, as compared to the gravitational timescale ($\delta t_{grav} \simeq 1/\sqrt{g\rho_{ns}} \gtrsim 10^{-4}$ s), to make it longer the timescale for coulombian (electrostatic) neutralization ($\delta t \simeq \lambda_{debye}/c \lesssim 10^{-20}$ s), which would otherwise take place at the phase transition created inner crust-upper mantle charge interface (\textit{separatrix}) inside the p-ns, much earlier than the gravitational core collapse would take over. In such stalled state of charge separation the aftermath of gravitational collapse of the p-ns inner core can be an astrophysical charged black hole.

I discuss the multiple imaging properties, the geometry of caustics and other lensing features of black holes. In particular, I consider an exact lens map for non-rotating black holes and i discuss how schwarzschild black holes can be distinguished, by way of lensing observations, from other black holes and from non-collapsed compact objects.

In this talk we consider a relativistic heavy quark which moves in the quark-gluon plasmas. By using the holographic methods, we analyze the langevin diffusion process of this relativistic heavy quark. This heavy quark is described by a trailing string attached to a flavor brane and moving at constant velocity. The fluctuations of this string are related to the thermal correlators and the correlation functions are precisely the kinds of objects that we compute in the gravity dual picture. We obtain the action of the trailing string in hyperscaling violation backgrounds and we then find the equations of motion. These equations lead us to construct the langevin correlator which helps us to obtain the langevin constants. Using the langevin correlators we derive the densities spectral and simple analytic expressions in the small and large frequency limits. We examine our works for planar and $r$-charged black holes with hyperscaling violation and find new constraints on $\theta$ in the presence of velocity $v$.

We consider the charged black hole with a scalar Eld which is coupled by gravity in (2+1)-dimension. We compute the logarithmic corrections with corresponding system with two approaches: the Rst method we take advantage from thermodynamic prop- erties. The second method we use the metric function which is suggested by conformal Eld theory. Finally, we compare the results of two approaches with each other.

C. Sigismondi, S. C. Boscardin, A. H. Andrei, J. L. Penna, E. Reis-neto, V. A. D'avila, M. Emilio
The debate around the accuracy of ground-based and space measurements of the solar figure is still open, after the recent publication of all astrolabe campaigns. Direct measurements of a signal compatible with the solar rotation time, and seasonal effects are discussed. The comparison between earth and space results is examined in light of relativistic consequences.

The time evolution of a self-gravitating u(1) cosmic string on a warped 5d axially symmetric spacetime is numerically investigated. Although cosmic strings are theoretically predicted in 4d general relativistic models, there is still no observational evidence of their existence. From recent observations of the cosmic microwave background it is concluded that these cosmic strings cannot provide a satisfactory explanation for the bulk of density perturbations. They even could not survive inflation. It is conjectured that only in a 5d warped brane world setting there will be observable imprint of these so-called cosmic superstrings on the induced effective 4d brane metric for values of the symmetry breaking scale larger than the gut values. The warp factor makes these strings consistent with the predicted mass per unit length on the brane. However, in a time-dependent setting, it seems that there is wave-like energy-momentum transfer to infinity on the brane, a high-energy brane world behavior. This in contrast to earlier results in approximation models. Evidence of this information from the bulk geometry could be found in the gravitational cosmic background radiation via gravitational wave energy momentum affecting the brane evolution. Fluctuations of the brane when there is a u(1) gauge field present, are comparable with the proposed low brane tension fluctuations, or branons, whose relic abundance can be a dark matter candidate. We briefly made a connection with the critical behavior at the threshold of black hole formation found by choptuik several decades ago in self gravitating time dependent scalar field models. The critical distinction between dispersion of the scalar waves and singular behavior fade away when a time dependent warp factor is present.

A. Stepanian, M. Kohandel
First the existence of different unitary inequivalent representations in the quantum field theory is discussed. Then it is shown that how they can play a major role for us to understand some phenomena such as hawking effect.

We investigate the semi-classical Schwinger pair production in pulsed rotating fields with experimental investigation of the effect in mind. To do so we use the WKB-approximation. We find an analytic solution for the momentum spectrum of produced pairs for the constant rotating field. For the more evolved case of a rotating Sauter-pulse we solve the problem numerically and propose a new approximative analytic method. Additionally we compare our results to the ones obtained by using the Wigner-formalism.

An infrared-based sample of very high energy gamma-ray blazar candidates blazars are the dominant type of extragalactic sources at microwave and at gamma-ray energies. In the most energetic part of the electromagnetic spectrum (e>100gev) a large fraction of high galactic latitude sources are blazars of the high synchrotron peaked (hsp) type, that is bl lac objects with synchrotron power peaking in the uv or in the x-ray band. Building new large samples of hsp blazars is key to understand the properties of jets under extreme conditions, and to study the demographics and the peculiar cosmological evolution of these sources. Identify possible sources of tev photons hsp blazars are remarkably rare, with only a few hundreds of them expected to be above the sensitivity limits of currently available surveys, some of which include hundreds of millions of sources. To find these very uncommon objects, we have devised a method that combines allwise survey data with multi-frequency selection criteria. The sample was defined starting from a primary list of infrared colour-colour selected sources from the allwise all sky survey database, and applying further restrictions on ir-radio and ir-x-ray flux ratios. Using a polynomial fit to the multi-frequency data (radio to x-ray) we estimated synchrotron peak frequencies and fluxes of each object. We assembled a sample including 997 sources, which is currently the largest existing list of confirmed and candidates hsp blazars. All objects are expected to radiate up to the highest gamma-ray photon energies. In fact, 296 of these are confirmed emitters of gev photons (based on fermi-lat catalogues), and 33 have already been detected in the tev band. Probably all sources in the sample are within reach of the upcoming cherenkov telescope array (cta), and many may be detectable even by the current generation of cherenkov telescopes during flaring episodes. The sample includes 395 previously known objects, 155 new identifications, and 447 hsp candidates for which no optical spectra is available yet.

Observations of long Gamma-ray Bursts may be explained using the paradigm of Induced Gravitational Collapse (IGC). IGC is based on a binary system consisting of a massive star and a neutron star. As the massive star undergoes a supernova explosion, the expanding supernova shell induces Bondi-Hoyle accretion onto the neutron-star companion. The initial x-ray emission seen in long GRBs may be due the heating of material as it accretes onto the neutron star. We have run numerical simulations of such super-Eddington accretion onto a neutron star. We have utilized a relativistic hydrodynamic model with flux limited neutrino transport and a realistic nuclear equation of state. We have modeled various accretion rates to analyze whether this process can contribute to the observed X-ray luminosity and light curve.

Y. Wu, S. S. Xue
The nonlinear breit-wheeler process of electron-positron pair production off a probe photon colliding with a low-frequency and a high-frequency electromagnetic wave that propagate in the same direction is analyzed. We calculate the pair-production probability and the spectra of the created pair in the nonlinear breit-wheeler processes of pair production off a probe photon colliding with two plane waves and one plane wave. The differences between these two cases are discussed. We show the highly multi-photon phenomenon that is evident by the electron-positron pair absorbing photons from the low-frequency wave, in addition to one photon from the high-frequency wave. The result presented in this article shows a possible way to access to the observation of this highly multi-photon phenomenon of pair production even with the laser-beam intensity of order 10^18 w/cm^2.

To probe the non-linear effects of photon-photon interaction in quantum electrodynamics, we study the generation of circular polarized photons by the collision of two linearly polarized laser beams. In the framework of the Euler-Heisenberg effective Lagrangian and the quantum Boltzmann equation for the time evolution of the density matrix of polarization, we calculate the intensity of circular polarization generated by the collision of two linearly polarized laser beams and estimate the rate of generation that is proportional to α^2.
As a result, we show that the generated circular polarization can be experimentally measured by two head-on colliding optical laser beams of a cross-sectional area 0.01 cm^2 and a laser pulse energy of ∼mJ, which are currently available in laboratories. Our study presents a valuable supplement to other theoretical and experimental frameworks for the study and measurement of the non-linear effects of photon-photon interaction in quantum electrodynamics.

R. Ruffini, S. S. Xue
We adopt a simplified model describing the collapse of a spherically thin capacitor to give an analytical description how gravitational energy is converted to both kinetic and electric energies in collapse. It is shown that (i) averaged kinetic and electric energies are the same order, about an half of gravitational energy of spherically thin capacitor in collapse; (ii) caused by radiating and rebuilding electric energy, gravitational collapse undergoes a sequence of "on and off" hopping steps in the microscopic compton scale. Although such a collapse process is still continuous in terms of macroscopic scales, it is slowed down as kinetic energy is reduced and collapsing time is about an order of magnitude larger than that of collapse process eliminating electric processes.

Gamma-Ray Bursts (GRBs) are the most powerful sources of electromagnetic radiation in the Universe. There are many open questions about their origin and their nature, and the answers should be searched in the large amount of data collected during these last years. We focused on the study of the their X-ray and optical afterglow properties, as observed by the Swift X-Ray Telescope (XRT) and ground-based optical telescopes. We investigated the observer and rest-frame properties of all GRBs observed by Swift between December 2004 and December 2010 with spectroscopic redshift through a comprehensive statistical analysis of the XRT light-curves of GRBs carried out in a model-independent way. We found out a three parameter correlation that is followed both by short and long GRBs. We also carried out a systematic analysis of the optical data available in literature for the same GRBs to investigate the GRB emission mechanisms and to study their environment properties. Our analysis shows that the gas-to-dust ratios of GRBs are larger than the values calculated for the Milky Way, the Large Magellanic Cloud, and the Small Magellanic Cloud. In this talk I will show the major results of the analysis of this large set of data.