Capturing Electrons and Asteroids
What do asteroid capture and double ionization have in common? A great deal, it turns out: A circularly polarized (CP) laser field hurls ionized electrons back at the core in the same way that comets and interplanetary debris make their way to planets. According to conventional wisdom, a CP field suppresses collision-induced double ionization and high harmonic generation since ionized electrons spiral away and therefore cannot revisit the core. A few experiments carried out with rare gas atoms in the past confirmed this belief, and the matter would rest there if it weren't for conflicting experiments showing the signature of electron-electron correlation in the double ionization of magnesium. We reconcile these seemingly contradictory results by finding the conditions for an ionized electron to revisit the core to ionize more electrons (or recombine to generate high harmonics). Ionized electrons can return through a moving saddle point which arises from the joint actions of the Coulomb potential and the laser field. Our results imply that the so-called "recollision" or "three-step" model, which is the keystone of strong field physics in linearly polarized fields, can also be valid in circularly polarized ones.
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EP10647
To queue or not to queue? A social paradigm under the lens of
computational physics.
Why do certain cultures privilege ordered, one‑dimensional queues
before a ticket
counter while others tend to prefer two‑dimensional chaotic crowding:
is it only a matter of
social conventions? In this paper we introduce a simple agent‑based
Monte Carlo model
for assessing quantitatively issues of the like in crowd dynamics. Our
simulations show that,
while on average the two queuing habits yield equivalent series of
waiting times, in crowd‑queuing
inclined cultures your size is a plus ‑ the smaller agents get served
first. This effect may be
thought of as the equivalent of the Brazil nut effect as the agents
keep crowding and
redistributing round the counter. Besides the current application, our
model provides a simple,
yet powerful, alternative to the current molecular dynamics schemes
for the investigation of many
issues in crowd dynamics.
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CSR1022
PUTTING THE MASS BACK INTO THE PROTON
It has long been widely held that the ground-state of the strong-interaction piece of the Standard Model; namely, quantum chromodynamics, is enormously complicated, populated e.g., by a sea of quark-antiquark pairs. This so-called vacuum quark condensate is 5-times more dense than matter at the core of a neutron star. In this paper we show that there is an alternative to this conventional picture -- the ground state is empty! Owing to the remarkable property of quark and gluon confinement, the quark condensate is entirely contained within the pions, protons and other hadrons that constitute the strong-interaction's experimentally observed spectrum. Within quantum chromodynamics we demonstrate that there is no leakage from the hadrons, and thus, contrary to conventional wisdom, there are no space-time-independent condensates permeating the universe. Amongst its many consequences, this paradigmatic shift has a huge impact on the cosmological constant paradox: it resolves a 45-orders-of-magnitude conflict between quantum chromodynamics and experiment. The zero-point energy of the universe just got a lot smaller.
