784 research outputs found
Uniqueness of photon spheres in electro-vacuum spacetimes
In a recent paper, the authors established the uniqueness of photon spheres
in static vacuum asymptotically flat spacetimes by adapting Bunting and
Masood-ul-Alam's proof of static vacuum black hole uniqueness. Here, we
establish uniqueness of suitably defined sub-extremal photon spheres in static
electro-vacuum asymptotically flat spacetimes by adapting the argument of
Masood-ul-Alam. As a consequence of our result, we can rule out the existence
of electrostatic configurations involving multiple "very compact" electrically
charged bodies and sub-extremal black holes.Comment: 16 pages. This paper extends the photon sphere uniqueness result
obtained in arXiv:1504.05804 from the vacuum to the electro-vacuum setting.
While the general proof method is similar, a number of new nontrivial issues
aris
Radiation Generated by Charge Migration Following Ionization
Electronic many-body effects alone can be the driving force for an ultrafast
migration of a positive charge created upon ionization of molecular systems.
Here we show that this purely electronic phenomenon generates a characteristic
IR radiation. The situation when the initial ionic wave packet is produced by a
sudden removal of an electron is also studied. It is shown that in this case a
much stronger UV emission is generated. This emission appears as an ultrafast
response of the remaining electrons to the perturbation caused by the sudden
ionization and as such is a universal phenomenon to be expected in every
multielectron system.Comment: 5 pages, 4 figure
Strong interference effects in the resonant Auger decay of atoms induced by intense X-Ray fields
The theory of resonant Auger decay of atoms in a high intensity coherent
X-ray pulse is presented. The theory includes the coupling between the ground
state and the resonance due to an intense X-ray pulse, taking into account the
decay of the resonance and the direct photoionization of the ground state, both
populating the final ionic states coherently. The theory also considers the
impact of the direct photoionization of the resonance state itself which
typically populates highly-excited ionic states. The combined action of the
resonant decay and of the direct ionization of the ground state in the field
induces a non-hermitian time-dependent coupling between the ground and the
'dressed' resonance stats. The impact of these competing processes on the total
electron yield and on the 2s2p3p P spectator and
2s2p S participator Auger decay spectra of the Ne 1s3p
resonance is investigated. The role of the direct photoionization of the ground
state and of the resonance increases dramatically with the field intensity.
This results in strong interference effects with distinct patterns in the
electron spectra, different for the participator and spectator final states.Comment: 31 pages, 6 figure
Photon surfaces with equipotential time-slices
Photon surfaces are timelike, totally umbilic hypersurfaces of Lorentzian
spacetimes. In the first part of this paper, we locally characterize all
possible photon surfaces in a class of static, spherically symmetric spacetimes
that includes Schwarzschild, Reissner--Nordstr\"om, Schwarzschild-anti de
Sitter, etc., in dimensions. In the second part, we prove that any
static, vacuum, "asymptotically isotropic" -dimensional spacetime that
possesses what we call an "equipotential" and "outward directed" photon surface
is isometric to the Schwarzschild spacetime of the same (necessarily positive)
mass, using a uniqueness result by the first named author.Comment: 33 pages, 1 figure We have added a discussion of generating null
geodesics and related topics at the end of Section 3 and have simplified some
computation
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