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astrophysics in the UCLA plasma simulation group
     In the last decade, the field of astrophysics has been witness to a surge of fundamental discoveries driven by new detectors, new experimental techniques, and the increase of computational power. However, many of the mysteries of the universe still elude us: What is the fundamental mechanism behind gamma-ray bursts? Why is there a solar neutrino "deficit"? What is the nature of dark matter? Why do supernovae IIa explode (and why do the numerical models fail to predict strong and successful explosions)? Why are neutron stars born with velocities up to 2000 km/s?
Related Image:
supernova picture
Supernova 1987                                HST. WFPC2
PRC97-03   ST Sci OPO  January 14, 1997
J. Pun (NASA/GSFC), R Kirshner(CFA) and NASA
     A common link to most of these questions is the presence of neutrinos, in some cases with intensities in excess of 1028 W/cm^2, and luminosities in the range of 1054 erg/s. Under such extreme conditions, even the elusive weak interacting neutrinos perturb the background medium, and the back reaction of the medium then disturbs the neutrino transport. Thus, and only very recently [1], our group suggested that neutrinos propagating across a dense plasma can transfer some of their free energy to the collective modes of the plasma, through the electroweak analogues of electron/photon parametric instabilities. A laser beam with modest intensity (I ~ 1 W/cm2) can travel to the Moon, be reflected back to Earth, and collected in a telescope (by the way, this is the most accurate method to determine the distance from the Earth to the Moon). If the intensity of this photon beam is increased by eighteen orders of magnitude (increasing the energy of the laser pulse and shortening its duration), the laser beam will not even leave the lab, completely ionizing the air along the propagation path, and depositing almost all its energy in the plasma, being absorbed in distances not exceeding 1 cm. In the same way, intense fluxes of neutrinos can also deposit a significant amount of their free energy in the plasma.


project goals
     The goal of our research program is to develop the theoretical and numerical tools to describe the physics of collective neutrino-plasma interactions, and to determine the impact of neutrino driven instabilities in different astrophysical processes. In particular, we are interested in: (i) the long standing "stalled shock" problem in type IIa supernovae, and the possibility of the shock revival by anomalous neutrino heating; (ii) collective neutrino-plasma interactions in intense magnetic fields, connected with the birth velocity of neutron stars and gamma-ray generation, (iii) filamentation of neutrino beams, and formation of nonlinear structures in the lepton stage of the early universe
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     The semi-classical transport equation for the neutrinos, necessary to describe collective neutrino-plasma interactions, is formally equivalent to the Vlasov equation. The kinetic structure of the propagation equation leads naturally to a "Neutrino in Cell" numerical model. During the previous year, we have developed a general numerical model, describing the collisionless transport of quasi-particles (neutrinos or photons). We have compared the numerical model against known results for laser propagation in underdense plasmas, and we find very good agreement with theory and well tested fully explicit "Particle in Cell" codes. This opens the way to realistic simulations of collective neutrino-plasma interactions. In particular, we intend to determine the energy transferred from the neutrinos to the plasma, and validate estimates based on a quasi-linear theory of the neutrino-plasma coupling. The results from the quasi-linear analysis show that in supernovae IIa, neutrinos transfer up to 0.01 % of their energy (around 1 MeV/nucleon).

     The other important aspect is the nonlinear regime of the neutrino driven instability. In this regime, the simulation results will be invaluable, providing the insight to fully understand the saturation mechanism.

     This is an exciting, rich and unexplored field, where a wide variety of novel effects can be expected, and the questions and possibilities surpass the answers.


project results
Our work was featured as a Hot Topic in Plasma Physics at the APS Centennial Meeting (along with the Plasma Accelerator work of our group).

Press Release: http://www.aps.org/meet/CENT99/vpr/other-plasma.html

Work is partially supported by the National Science Foundation Grant AST - 9713234


related websites
 
Unsolved Problems in Astrophysics, the book: http://www.sns.ias.edu/~jnb/Books/Unsolved/unsolved.html
Preprints in Plasma Physics, Astrophysics, and everything else: http://xxx.lanl.gov/
Hubble Space Telescope: http://www.stsci.edu/

recent publications

[1] R.Bingham, J.M.Dawson, H.A.Bethe, and J.J.Su, Phys.Lett. A (1992)

The original idea for collective neutrino-plasma interactions and anomalous neutrino heating in SNIIa was first discussed here.

[2] R.Bingham, J.M.Dawson, H.A.Bethe, P.K.Shukla, and J.J.Su, Phys.Lett. A (1994)

The concept of the ponderomotive force of neutrinos as the coupling mechanism with the background plasma is introduced in this paper.

[3] J.M.Dawson, to appear in "New Worlds in Astroparticle Physics II" (World Scientific, Singapore, 1999), A.Mourao, M.Pimenta, and P.Sa, Eds.

The physical picture for neutrino driven streaming instabilities is described here.

[4] L.O.Silva, R.Bingham, J.M.Dawson, W.B.Mori, Phys. Rev. E 59, 2273-2280 (1999);

Generalization of the ponderomotive force of neutrinos for arbitrary background species, neutrino flavors, and magnetic field configurations.

[5] P.K.Shukla, L.O.Silva, H.A.Bethe, R.Bingham, J.M.Dawson, L.Stenflo, J.T.Mendonca, H.E.Dalhed, Plasma Phys. Controll. Fusion 41 A699-A707 (1999)

Review paper presenting some of the recent results based on a kinetic description of the neutrinos, and also with references to a series of papers extending the results of [1].

[6] L.O.Silva, R.Bingham, J.M.Dawson, P.K.Shukla, N.L.Tsintsadze, J.T.Mendonca, Phys.Rev. D15 (August 1999).

Comment on a previous Finite Temperature Quantum Field Theory calculation of the ponderomotive force of neutrinos.

[7] L.O.Silva, R.Bingham, J.M.Dawson, J.T.Mendonca, and P.K.Shukla, Astrophysical Journal, to appear (1999)

A covariant kinetic theory for collisionless neutrino-plasma interactions.

[8] L.O.Silva, R.Bingham, J.M.Dawson, J.T.Mendonca, and P.K.Shukla, Phys. Rev.Lett., to appear (1999)

Neutrino driven streaming instabilities in dense plasmas.
 
 

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