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Register a new userTwo-photon annihilation in the pair formation cascades in pulsar polar caps
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The importance of the photon-photon pair production process ($gamma+ gamma^{prime}to e^{+}+e^{-}$) to form pair production cascades in pulsar polar caps is investigated within the framework of the Ruderman-Sutherland vacuum gap model. It is found that this process is unimportant if the polar caps are not hot enough, but will play a non-negligible role in the pair formation cascades when the polar cap temperatures are in excess of the critical temperatures, $T_{cri}$, which are around $4times 10^6K$ when $P=0.1$s and will slowly increase with increasing periods. Compared with the $gamma-B$ process, it is found that the two-photon annihilation process may ignite a central spark near the magnetic pole, where $gamma-B$ sparks can not be formed due to the local weak curvatures. This central spark is large if the gap is dominated by the ``resonant ICS mode. The possible connection of these central sparks with the observed pulsar ``core emission components is discussed.
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Pulsar magnetospheres are thought to be filled with electron-positron plasma generated in pair cascades. The driving mechanism of these cascades is the emission of gamma-ray photons and their conversion into pairs via Quantum Electrodynamics (QED) processes. In this work, we present 2D particle-in-cell simulations of pair cascades in pulsar polar caps with realistic magnetic field geometry that include the relevant QED processes from first principles. Our results show that, due to variation of magnetic field curvature across the polar cap, pair production bursts self-consistently develop an inclination with respect to the local magnetic field that favors the generation of coherent electromagnetic modes with properties consistent with pulsar radio emission. We show that this emission is peaked along the magnetic axis and close to the polar cap edge and may thus offer an explanation for the core and conal components of pulsar radio emission.
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We calculate the cross section of Higgs boson pair production at a photon collider in the two Higgs doublet model. We focus on the scenario in which the lightest CP even Higgs boson ($h$) has the standard model like couplings to the gauge bosons. We take into account the one-loop correction to the $hhh$ coupling as well as additional one-loop diagrams due to charged Higgs bosons to the $gammagammato hh$ helicity amplitudes. It is found that the full cross section can be enhanced by both these effects to a considerable level. We discuss the impact of these corrections on the $hhh$ coupling measurement at the photon collider.
Entangled two-photon absorption (ETPA) has recently become a topic of lively debate, mainly due to the apparent inconsistencies in the experimentally-reported ETPA cross sections of organic molecules. In this work, we provide a thorough experimental study of ETPA in the organic molecules Rhodamine B (RhB) and Zinc Tetraphenylporphirin (ZnTPP). The goal of this contribution is twofold: on one hand, it seeks to reproduce the results of previous experimental reports and, on the other, it aims to determine the effects of different temporal correlations -- introduced as a controllable time-delay between the photons to be absorbed -- on the strength of the ETPA signal. In our experiment, the samples are excited by entangled pairs produced by type-I SPDC, with a spectral distribution centered at 810 nm. Surprisingly, and contrary to what was expected, the time delay did not produce in our experiments any systematic change in the cross-sections when monitoring the ETPA signal using a transmission measurement scheme. As a plausible cause of this unexpected result, we argue that the photon-pair flux, typically-used in these experiments, is not sufficient to promote the two-photon absorption process in these molecules. This suggests that the actual absorption cross-section values are lower than those previously reported, and therefore do not lead to a measurable ETPA effect for the transmission method.
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