5,699 research outputs found
Comments on claimed risk from metastable black holes
In a recent note, arXiv:0808.1415, it was argued that a hypothetical
metastable black hole scenario could pose collider risk not excluded by our
previous study. We comment on inconsistency of this proposed scenario.Comment: 3 pages; comment on arXiv:0808.141
Multi-Photon Amplitudes for Next-to-Leading Order QCD
We present the tree-level amplitudes involving one, two and three photons
that are required for next-to-leading order QCD calculations of production
rates of three final-state particles. We also present the required one-loop
amplitudes in terms of previously published results.Comment: LaTeX, 22 page
Four Statements about the Fourth Generation
This summary of the Workshop "Beyond the 3-generation SM in the LHC era"
presents a brief discussion of the following four statements about the fourth
generation: 1) It is not excluded by EW precision data; 2) It addresses some of
the currently open questions; 3) It can accommodate emerging possible hints of
new physics; 4) LHC has the potential to discover or fully exclude it.Comment: Summary of the "Beyond the 3-generation SM in the LHC era" Workshop,
CERN, September 4-5, 2008; 7 pages. V2: updated bibliography and minor typos
fixed. To appear in PMC Physics
The heavy quark search at the LHC
We explore further the discovery potential for heavy quarks at the LHC, with
emphasis on the and of a sequential fourth family associated with
electroweak symmetry breaking. We consider QCD multijets, ,
and single backgrounds using event generation based on
improved matrix elements and low sensitivity to the modeling of initial state
radiation. We exploit a jet mass technique for the identification of
hadronically decaying 's and 's, to be used in the reconstruction of the
or mass. This along with other aspects of event selection can reduce
backgrounds to very manageable levels. It even allows a search for both
and in the absence of -tagging, of interest for the early running of
the LHC. A heavy quark mass of order 600 GeV is motivated by the connection to
electroweak symmetry breaking, but our analysis is relevant for any new heavy
quarks with weak decay modes.Comment: 12 pages, 7 figure
Statistics and UV-IR Mixing with Twisted Poincare Invariance
We elaborate on the role of quantum statistics in twisted Poincare invariant
theories. It is shown that, in order to have twisted Poincare group as the
symmetry of a quantum theory, statistics must be twisted. It is also confirmed
that the removal of UV-IR mixing (in the absence of gauge fields) in such
theories is a natural consequence.Comment: 13 pages, LaTeX; typos correcte
Cosmological lepton asymmetry with a nonzero mixing angle \theta_{13}
While the baryon asymmetry of the Universe is nowadays well measured by
cosmological observations, the bounds on the lepton asymmetry in the form of
neutrinos are still significantly weaker. We place limits on the relic neutrino
asymmetries using some of the latest cosmological data, taking into account the
effect of flavor oscillations. We present our results for two different values
of the neutrino mixing angle \theta_{13}, and show that for large \theta_{13}
the limits on the total neutrino asymmetry become more stringent, diluting even
large initial flavor asymmetries. In particular, we find that the present
bounds are still dominated by the limits coming from Big Bang Nucleosynthesis,
while the limits on the total neutrino mass from cosmological data are
essentially independent of \theta_{13}. Finally, we perform a forecast for
COrE, taken as an example of a future CMB experiment, and find that it could
improve the limits on the total lepton asymmetry approximately by up to a
factor 6.6.Comment: 11 pages, 7 figures, 5 tables. v2: updated COrE specifications. v3:
matches Phys. Rev. D accepted versio
Independent measurement of the top quark mass and the light- and bottom-jet energy scales at hadron colliders
A method for the simultaneous determination of the energy scales for b-quark
jets and light jets, the jet energy resolution, and the top quark mass at
hadron colliders is presented. The method exploits the unique kinematics of
events with top-antitop pair production, where one of the top quarks involves a
leptonic and one a hadronic W boson decay. The paper shows a feasibility study
of how this simultaneous measurement can be performed at the upcoming LHC
experiments ATLAS and CMS.Comment: 10 pages, 5 figure
Evolution and nucleosynthesis of primordial low mass stars
We discuss in detail the evolutionary properties of low mass stars M< 1
M(Solar) having metallicity lower than Z=10^(-6) from the pre- main sequence up
to (almost) the end of the Asymptotic Giant Branch phase. We also discuss the
possibility that the large [C,N/Fe] observed on the surface of the most Iron
poor star presently known, HE0107-5240, may be attributed to the autopollution
induced by the penetration of the He convective shell into the H rich mantle
during the He core flash of a low mass, very low metallicity star. On the basis
of a quite detailed analysis, we conclude that the autopollution scenario
cannot be responsible for the observed chemical composition of HE0107-5240
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