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

The heavy quark search at the LHC

We explore further the discovery potential for heavy quarks at the LHC, with emphasis on the $t'$ and $b'$ of a sequential fourth family associated with electroweak symmetry breaking. We consider QCD multijets, $t\bar{t}+\rm{jets}$, $W+\rm{jets}$ and single $t$ 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 $W$'s and $t$'s, to be used in the reconstruction of the $t'$ or $b'$ mass. This along with other aspects of event selection can reduce backgrounds to very manageable levels. It even allows a search for both $t'$ and $b'$ in the absence of $b$-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

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

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

t' at the LHC: the physics of discovery

A search for a fourth family at the LHC is presently a low priority, but we argue that an effective search can be conducted early with only a few inverse femtobarns of data. We discuss a method based on invariant masses of single jets for identifying the $W$'s originating from heavy quark decays. This can significantly increase signal to background in the reconstruction of the $t'$ mass. We also study the various types of physics that can impact the background estimate, most notably higher order effects, initial state radiation, and models of the underlying event.Comment: 16 pages, 12 figures, small improvements, version to appear in JHE

Multiphoton Production at High Energies in the Standard Model I

We examine multiphoton production in the electroweak sector of the Standard Model in the high energy limit using the equivalence theorem in combination with spinor helicity techniques. We obtain recursion relations for currents consisting of a charged scalar, spinor, or vector line that radiates $n$ photons. Closed form solutions to these recursion relations for arbitrary $n$ are presented for the cases of like-helicity and one unlike-helicity photon production. We apply the currents singly and in pairs to obtain amplitudes for processes involving the production of $n$ photons with up to two unlike helicities from a pair of charged particles. The replacement of one or more photons by transversely polarized $$Z$-bosons is also discussed.Comment: 75 pages, CLNS 91/111

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