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P. Elmfors

Publications and source records attributed to P. Elmfors.

5 recordsLinked to original sources

Wire scanners in low energy accelerators

Fast wire scanners are today considered as part of standard instrumentation in high energy synchrotrons. The extension of their use to synchrotrons working at lower energies, where Coulomb scattering can be important and the transverse beam size is large, introduces new complications considering beam heating of the wire, composition of the secondary particle shower and geometrical consideration in the detection set-up. A major problem in treating these effects is that the creation of secondaries in a thin carbon wire by a energetic primary beam is difficult to describe in an analytical way. We are here presenting new results from a full Monte Carlo simulation of this process yielding information on heat deposited in the wire, particle type and energy spectrum of secondaries and angular dependence as a function of primary beam energy. The results are used to derive limits for the use of wire scanners in low energy accelerators.

physics.acc-ph

Condensation and Magnetization of the Relativistic Bose Gas

We present a simple proof of the absence of Bose--Einstein condensation of a relativistic boson gas, in any finite local magnetic field in less than five dimensions. We show that the relativistic charged boson gas exhibit a genuine Meissner--Ochsenfeld effect of the Schafroth form at fixed supercritical density. As in the well--known non--relativistic case, this total expulsion of a magnetic field is caused by the condensation of the Bose gas at vanishing magnetic field. The result is discussed in the context of kaon condensation in neutron stars.

hep-ph

On the Non-Equilibrium Early Universe

We study non--equilibrium ensemble corrections to particle masses and the effective potential in the early universe, using a uniform momentum distribution as an example. The resulting thermalization temperature is computed assuming \sm degrees of freedom, and it is always found to be below $5\times 10^{14}$ GeV, implying that GUT phase transitions typically take place out of equilibrium. For the abelian Higgs model we find that the phase transition is of second order if it occurs before equilibration, in contrast to the first order equilibrium phase transition.

hep-ph

Real-Time Thermal Propagators and the QED Effective Action for an External Magnetic Field

The thermal averaged real-time propagator of a Dirac fermion in a static uniform magnetic field $B$ is derived. At non-zero chemical potential and temperature we find explicitly the effective action for the magnetic field, which is shown to be closely related to the Helmholz free energy of a relativistic fermion gas, and it exhibits the expected de\ Haas -- van\ Alphen oscillations. An effective QED coupling constant at finite temperature and density is derived, and compared with renormalization group results. We discuss some astrophysical implications of our results.

hep-ph

Generalizations of the thermal Bogoliubov transformation

The thermal Bogoliubov transformation in thermo field dynamics is generalized in two respects. First, a generalization of the $α$--degree of freedom to tilde non--conserving representations is considered. Secondly, the usual $2\times2$ Bogoliubov matrix is extended to a $4\times4$ matrix including mixing of modes with non--trivial multiparticle correlations. The analysis is carried out for both bosons and fermions.

hep-th