948 research outputs found
Experimental Signatures of Fermiophobic Higgs bosons
The most general Two Higgs Doublet Model potential without explicit CP
violation depends on 10 real independent parameters. Excluding spontaneous CP
violation results in two 7 parameter models. Although both models give rise to
5 scalar particles and 2 mixing angles, the resulting phenomenology of the
scalar sectors is different. If flavour changing neutral currents at tree level
are to be avoided, one has, in both cases, four alternative ways of introducing
the fermion couplings. In one of these models the mixing angle of the CP even
sector can be chosen in such a way that the fermion couplings to the lightest
scalar Higgs boson vanishes. At the same time it is possible to suppress the
fermion couplings to the charged and pseudo-scalar Higgs bosons by
appropriately choosing the mixing angle of the CP odd sector. We investigate
the phenomenology of both models in the fermiophobic limit and present the
different branching ratios for the decays of the scalar particles. We use the
present experimental results from the LEP collider to constrain the models.Comment: 23 pages, 18 figures included, newer experimental data include
Top quark loop corrections to the decay in the Two Higgs Doublet Model
We calculate the decay width for the process up to order
in the framework of the Two Higgs Doublet Model. We argue that for some
reasonable choice of the free parameters the contribution from the one-loop
graphs can be as large as 40%.Comment: 9 pages (in a4wide), tex with figures attached, uuencoded tared gzip
file Postscript file also available at
http://thep.physik.uni-mainz.de/~brueche
The Expected Perimeter in Eden and Related Growth Processes
Following Richardson and using results of Kesten on First-passage
percolation, we obtain an upper bound on the expected perimeter in an Eden
Growth Process. Using results of the author from a problem in Statistical
Mechanics, we show that the average perimeter of the lattice animals resulting
from a very natural family of "growth histories" does not obey a similar bound.Comment: 11 page
XLOOPS -- A Program Package calculating One- and Two-Loop Feynman Diagrams
The aim of XLOOPS is to calculate one-particle irreducible Feynman diagrams
with one or two closed loops for arbitrary processes in the Standard model of
particles and related theories. Up to now this aim is realized for all one-loop
diagrams with at most three external lines and for two-loop diagrams with two
external lines.Comment: 84 pages, Postscript, program package and this manual also available
at http://wwwthep.physik.uni-mainz.de/~xloops/, minor changes and bug fixes
are included no
Were rivers flowing across the Sahara during the last interglacial? Implications for human migration through Africa.
Human migration north through Africa is contentious. This paper uses a novel palaeohydrological and hydraulic modelling approach to test the hypothesis that under wetter climates c.100,000 years ago major river systems ran north across the Sahara to the Mediterranean, creating viable migration routes. We confirm that three of these now buried palaeo river systems could have been active at the key time of human migration across the Sahara. Unexpectedly, it is the most western of these three rivers, the Irharhar river, that represents the most likely route for human migration. The Irharhar river flows directly south to north, uniquely linking the mountain areas experiencing monsoon climates at these times to temperate Mediterranean environments where food and resources would have been abundant. The findings have major implications for our understanding of how humans migrated north through Africa, for the first time providing a quantitative perspective on the probabilities that these routes were viable for human habitation at these times
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