43,853 research outputs found
The Global Comparators Project: International comparison of 30-day In-hospital mortality by day of the week
Heavy neutralino relic abundance with Sommerfeld enhancements - a study of pMSSM scenarios
We present a detailed discussion of Sommerfeld enhancements in neutralino
dark matter relic abundance calculations for several popular benchmark
scenarios in the general MSSM. Our analysis is focused on models with heavy
wino- and higgsino-like neutralino LSP and models interpolating between these
two scenarios. This work is the first phenomenological application of effective
field theory methods that we have developed in earlier work and that allow for
the consistent study of Sommerfeld enhancements in non-relativistic neutralino
and chargino co-annihilation reactions within the general MSSM, away from the
pure-wino and pure-higgsino limits.Comment: 38 pages, 14 figures, 3 table
Electroweak non-resonant corrections to top pair production close to threshold
The production of W+ W- b bbar from e+ e- collisions at energies close to the
t tbar threshold is dominated by the resonant process with a nearly on-shell t
tbar intermediate state. The W b pairs in the final state can also be reached
through the decay of off-shell tops or through background processes containing
no or only single top quarks. This non-resonant production starts to contribute
at NLO to the W+ W- b bbar total cross section in the non-relativistic
power-counting v ~ alpha_s ~ sqrt(alpha_EW). The NLO non-resonant corrections
presented in this talk represent the non-trivial NLO electroweak corrections to
the e+ e- -> W+ W- b bbar cross section in the top anti-top resonance region.
In contrast to the QCD corrections which have been calculated (almost) up to
NNNLO, the parametrically larger NLO electroweak contributions have not been
completely known so far, but are mandatory for the required accuracy at a
future linear collider. We consider the total cross section of the e+ e- -> W+
W- b bbar process and additionally implement cuts on the invariant masses of
the W+ b and W- bbar pairs.Comment: Talk presented at the 35th International Conference of High Energy
Physics - ICHEP2010, July 22-28, 2010, Paris France. 4 pages, 2 figure
Non-relativistic pair annihilation of nearly mass degenerate neutralinos and charginos I. General framework and S-wave annihilation
We compute analytically the tree-level annihilation rates of a collection of
non-relativistic neutralino and chargino two-particle states in the general
MSSM, including the previously unknown off-diagonal rates. The results are
prerequisites to the calculation of the Sommerfeld enhancement in the MSSM,
which will be presented in subsequent work. They can also be used to obtain
concise analytic expressions for MSSM dark matter pair annihilation in the
present Universe for a large number of exclusive two-particle final states.Comment: LATeX, 24 pages (+ 25 pages Appendix), 11 figures; v2 - replaced
incorrect version of Fig. 4 and fixed typos listed in the JHEP erratu
The Schur-Horn theorem for operators and frames with prescribed norms and frame operator
Let be a Hilbert space. Given a bounded positive definite
operator on , and a bounded sequence of non negative real numbers, the pair is
frame admissible, if there exists a frame on
with frame operator , such that , . We relate the existence of such frames with the Schur-Horn
theorem of majorization, and give a reformulation of the extended version of
Schur-Horn theorem, due to A. Neumann. We use it to get necessary conditions
(and to generalize known sufficient conditions) for a pair ,
to be frame admissible.Comment: To appear in Illinois Journal of Mat
Two charges on plane in a magnetic field: special trajectories
A classical mechanics of two Coulomb charges on a plane and
subject to a constant magnetic field perpendicular to a plane is
considered. Special "superintegrable" trajectories (circular and linear) for
which the distance between charges remains unchanged are indicated as well as
their respectful constants of motion. The number of the independent constants
of motion for special trajectories is larger for generic ones. A classification
of pairs of charges for which special trajectories occur is given. The special
trajectories for three particular cases of two electrons, (electron -
positron), (electron - -particle) are described explicitly.Comment: 22 pages, 5 figure
Type Ia supernova counts at high z: signatures of cosmological models and progenitors
Determination of the rates at which supernovae of Type Ia (SNe Ia) occur in
the early Universe can give signatures of the time spent by the binary
progenitor systems to reach explosion and of the geometry of the Universe.
Observations made within the Supernova Cosmology Project are already providing
the first numbers. Here it is shown that, for any assumed SNe Ia progenitor,
SNe Ia counts up to are useful tests of the SNe Ia
progenitor systems and cosmological tracers of a possible non-zero value of the
cosmological constant, . The SNe Ia counts at high redshifts compare
differently with those at lower redshifts depending on the cosmological model.
Flat --dominated universes would show a more significant
increase of the SNe Ia counts at than a flat,
universe. Here we consider three sorts of universes: a flat universe with
, , ;
an open universe with , ,
; and a flat, --dominated universe with , , ). On the
other hand, the SNe Ia counts from one class of binary progenitors (double
degenerate systems) should not increase steeply in the to range,
contrary to what should be seen for other binary progenitors. A measurement of
the SNe Ia counts up to is within reach of ongoing SNe Ia searches
at high redshifts.Comment: 16 pages, incl. 2 figures. To appear in ApJ (Letters
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