Nonlinear optics in strongly magnetized pair plasma, with applications to FRBs. (arXiv:2001.09210v1 [astro-ph.HE])

<a href="http://arxiv.org/find/astro-ph/1/au:+Lyutikov_M/0/1/0/all/0/1">Maxim Lyutikov</a> (Purdue University)

Intense radiation field can modify plasma properties, the corresponding

refractive index, and lead to such nonlinear propagation effects as

self-focusing. We estimate the corresponding effects in pair plasma, both in

unmagnetized and strongly magnetically dominated case. First, in the

unmagnetized pair plasma the ponderomotive force does not lead to charge

separation, but to density depletion. Second, for astrophysically relevant

plasmas of pulsar magnetospheres, (and possible loci of Fast Radio Bursts),

where cyclotron frequency $omega_B$ dominates over plasma frequency $omega_p$

and the frequency of the electromagnetic wave, $omega_B gg omega_p,,

omega$, we show that (i) there is virtually no nonlinearity due to changing

effective mass in the field of the wave; (ii) ponderomotive force is $F_p^{(B)}

=- {m_e c^2}/({4 B_0^2}) nabla E^2$; it is reduced by a factor

$(omega/omega_B)^2$ if compared to the unmagnetized case ($B_0$ is the

external magnetic field and $E$ is the electric field of the wave); (iii) for

radiation beam propagating along constant magnetic field in pair plasma with

density $n_pm$, the ponderomotive force leads to appearance of circular

currents that lead to the decrease of the field within the beam by a factor

$Delta B/B_0 = 2pi n_pm m_e c^2 {E^2}/{B_0^4}$. Applications to the physics

of FRBs are discussed; we conclude that for parameters of FRB’s the dominant

magnetic field completely suppresses nonlinear radiation effects.

Intense radiation field can modify plasma properties, the corresponding

refractive index, and lead to such nonlinear propagation effects as

self-focusing. We estimate the corresponding effects in pair plasma, both in

unmagnetized and strongly magnetically dominated case. First, in the

unmagnetized pair plasma the ponderomotive force does not lead to charge

separation, but to density depletion. Second, for astrophysically relevant

plasmas of pulsar magnetospheres, (and possible loci of Fast Radio Bursts),

where cyclotron frequency $omega_B$ dominates over plasma frequency $omega_p$

and the frequency of the electromagnetic wave, $omega_B gg omega_p,,

omega$, we show that (i) there is virtually no nonlinearity due to changing

effective mass in the field of the wave; (ii) ponderomotive force is $F_p^{(B)}

=- {m_e c^2}/({4 B_0^2}) nabla E^2$; it is reduced by a factor

$(omega/omega_B)^2$ if compared to the unmagnetized case ($B_0$ is the

external magnetic field and $E$ is the electric field of the wave); (iii) for

radiation beam propagating along constant magnetic field in pair plasma with

density $n_pm$, the ponderomotive force leads to appearance of circular

currents that lead to the decrease of the field within the beam by a factor

$Delta B/B_0 = 2pi n_pm m_e c^2 {E^2}/{B_0^4}$. Applications to the physics

of FRBs are discussed; we conclude that for parameters of FRB’s the dominant

magnetic field completely suppresses nonlinear radiation effects.

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