40 research outputs found
Electron-positron pairs in physics and astrophysics: from heavy nuclei to black holes
From the interaction of physics and astrophysics we are witnessing in these
years a splendid synthesis of theoretical, experimental and observational
results originating from three fundametal physical processes. They were
originally proposed by Dirac, by Breit and Wheeler and by Sauter, Heisenberg,
Euler and Schwinger. The vacuum polarization process in strong electromagnetic
field, pioneered by Sauter, Heisenberg, Euler and Schwinger, introduced the
concept of critical electric field. It has been searched without success for
more than forty years by heavy-ion collisions in many of the leading particle
accelerators worldwide. The novel situation today is that these same processes
can be studied on a much more grandiose scale during the gravitational collapse
leading to the formation of a black hole being observed in Gamma Ray Bursts.
This report is dedicated to the scientific race in act. The theoretical and
experimental work developed in Earth-based laboratories is confronted with the
theoretical interpretation of space-based observations of phenomena originating
on cosmological scales. What has become clear in the last ten years is that all
the three above mentioned processes, duly extended in the general relativistic
framework, are necessary for the understanding of the physics of the
gravitational collapse to a black hole. Vice versa, the natural arena where
these processes can be observed in mutual interaction and on an unprecedented
scale, is indeed the realm of relativistic astrophysics.Comment: to appear in Physics Reports, corrected proof
Pauli blocking effects on pair creation in strong electric field
The process of electron-positron pair creation and oscillation in uniform
electric field is studied, taking into account Pauli exclusion principle.
Generally, we find that pair creation is suppressed, hence coherent
oscillations occur on longer time scales. Considering pair creation in already
existing electron-positron plasma we find that the dynamics depends on pair
distribution function. We considered Fermi-Dirac distribution of pairs and
found that for small temperatures pair creation is suppressed, while for small
chemical potentials it increases: heating leads to enhancement of pair
creation.Comment: Accepted for publication in Physical Review
Pair creation in hot electrosphere of compact astrophysical objects
The mechanism of pair creation in electrosphere of compact astrophysical
objects such as quark stars or neutron stars is revisited, paying attention to
evaporation of electrons and acceleration of electrons and positrons,
previously not addressed in the literature. We perform a series of numerical
simulations using the Vlasov-Maxwell equations. The rate of pair creation
strongly depends on electric field strength in the electrosphere. Despite Pauli
blocking is explicitly taken into account, we find no exponential suppression
of the pair creation rate at low temperatures. The luminosity in pairs
increases with temperature and it may reach up to erg/s,
much larger than previously assumed
Equations of motion, initial and boundary conditions for GRB
We compare and contrast the different approaches to the optically thick
adiabatic phase of GRB all the way to the transparency. Special attention is
given to the role of the rate equation to be self consistently solved with the
relativistic hydrodynamic equations. The works of Shemi and Piran (1990),
Piran, Shemi and Narayan (1993), Meszaros, Laguna and Rees (1993) and Ruffini,
Salmonson, Wilson and Xue (1999,2000) are compared and contrasted. The role of
the baryonic loading in these three treatments is pointed out. Constraints on
initial conditions for the fireball produced by electro-magnetic black hole are
obtained.Comment: 10 pages, 8 figure
Baryonic loading and e^+e^- rate equation in GRB sources
The expansion of the electron-positron plasma in the GRB phenomenon is
compared and contrasted in the treatments of Meszaros, Laguna and Rees, of
Shemi, Piran and Narayan, and of Ruffini et al. The role of the correct
numerical integration of the hydrodynamical equations, as well as of the rate
equation for the electron-positron plasma loaded with a baryonic mass, are
outlined and confronted for crucial differences.Comment: 5 pages, 3 figures, to appear in the proceedings of "Relativistic
Astrophysics and Cosmology - Einstein's Legacy" meeting, November 7-11, 2005,
Munich, Germany, edited by B. Aschenbach, V. Burwitz, G. Hasinger, and B.
Leibundgu
Joint constraints on the lepton asymmetry of the Universe and neutrino mass from the Wilkinson Microwave Anisotropy Probe
We use the Wilkinson Microwave Anisotropy Probe (WMAP) data on the spectrum
of cosmic microwave background anisotropies to put constraints on the present
amount of lepton asymmetry L, parameterized by the dimensionless chemical
potential (also called degeneracy parameter) xi and on the effective number of
relativistic particle species. We assume a flat cosmological model with three
thermally distributed neutrino species having all the same mass and chemical
potential, plus an additional amount of effectively massless exotic particle
species. The extra energy density associated to these species is parameterized
through an effective number of additional species DeltaN_oth$. We find that
0<|xi|<1.1 and correspondingly 0<|L|<0.9 at 2sigma, so that WMAP data alone
cannot firmly rule out scenarios with a large lepton number; moreover, a small
preference for this kind of scenarios is actually found. We also discuss the
effect of the asymmetry on the estimation of other parameters and in particular
of the neutrino mass. In the case of perfect lepton symmetry, we obtain the
standard results. When the amount of asymmetry is left free, we find \sum m_nu
< 3.6 eV at 2sigma. Finally we study how the determination of |L| is affected
by the assumptions on DeltaN_oth. We find that lower values of the extra energy
density allow for larger values of the lepton asymmetry, effectively ruling
out, at 2sigma level, lepton symmetric models with DeltaN_oth=0.Comment: 11 pages, 2 figures. Uses RevTex4. Minor changes made to match
published versio