2,050 research outputs found

### A subtraction scheme for computing QCD jet cross sections at NNLO: regularization of real-virtual emission

We present a subtraction scheme for computing jet cross sections in
electron-positron annihilation at next-to-next-to-leading order accuracy in
perturbative QCD. In this second part we deal with the regularization of the
real-virtual contribution to the NNLO correction.Comment: 32 pages, LaTeX file, uses pstrick

### Antenna subtraction with hadronic initial states

The antenna subtraction method for the computation of higher order
corrections to jet observables and exclusive cross sections at collider
experiments is extended to include hadronic initial states. In addition to the
already known antenna subtraction with both radiators in the final state
(final-final antennae), we introduce antenna subtractions with one or two
radiators in the initial state (initial-final or initial-initial antennae). For
those, we derive the phase space factorization and discuss the allowed phase
space mappings at NLO and NNLO. We present integrated forms for all antenna
functions relevant to NLO calculations, and describe the construction of the
full antenna subtraction terms at NLO on two examples. The extension of the
formalism to NNLO is outlined.Comment: 33 pages, 3 figure

### Neutrino Splitting for Lorentz-Violating Neutrinos: Detailed Analysis

Lorentz-violating neutrino parameters have been severely constrained on the
basis of astrophysical considerations. In the high-energy limit, one generally
assumes a superluminal dispersion relation of an incoming neutrino of the form
E ~ |p|v, where E is the energy, p is the momentum and $v = sqrt(1 + delta) >
1. Lepton-pair creation due to a Cerenkov-radiation-like process (nu -> nu +
e^- + e^+) becomes possible above a certain energy threshold, and bounds on the
Lorentz-violating parameter delta can be derived. Here, we investigate a
related process, nu_i -> nu_i + nu_f + bar_nu_f, where nu_i is an incoming
neutrino mass eigenstate, while nu_f is the final neutrino mass eigenstate,
with a superluminal velocity that is slightly slower than that of the initial
state. This process is kinematically allowed if the Lorentz-violating
parameters at high energy differ for the different neutrino mass eigenstates.
Neutrino splitting is not subject to any significant energy threshold condition
and could yield quite a substantial contribution to decay and energy loss
processes at high energy, even if the differential Lorentz violation among
neutrino flavors is severely constrained by other experiments. We also discuss
the SU(2)-gauge invariance of the superluminal models and briefly discuss the
use of a generalized vierbein formalism in the formulation of the
Lorentz-violating Dirac equation.Comment: 17 pages; RevTeX; to appear in Physical Review

### The infrared structure of e+ e- --> 3 jets at NNLO reloaded

This paper gives detailed information on the structure of the infrared
singularities for the process e+ e- --> 3 jets at next-to-next-to-leading order
in perturbation theory. Particular emphasis is put on singularities associated
to soft gluons. The knowledge of the singularity structure allows the
construction of appropriate subtraction terms, which in turn can be implemented
into a numerical Monte Carlo program.Comment: 59 pages, additional comments added, version to be publishe

### Fully exclusive heavy quark-antiquark pair production from a colourless initial state at NNLO in QCD

We present a local subtraction scheme for computing next-to-next-to-leading order QCD corrections to the production of a massive quark-antiquark pair from a colourless initial state. The subtraction terms are built following the CoLoRFulNNLO method and refined in such a way that their integration gives rise to compact, fully analytic expressions. All ingredients necessary for a numerical implementation of our subtraction scheme are provided in detail. As an example, we calculate the fully differential decay rate of the Standard Model Higgs boson to massive bottom quarks at next-to-next-to-leading order accuracy in perturbative QCD

### Exact top Yukawa corrections to Higgs boson decay into bottom quarks

In this letter we present the results of the exact computation of
contributions to the Higgs boson decay into bottom quarks that are proportional
to the top Yukawa coupling. Our computation demonstrates that approximate
results already available in the literature turn out to be particularly
accurate for the three physical mass values of the Higgs boson, the bottom and
top quarks. Furthermore, contrary to expectations, the impact of these
corrections on differential distributions relevant for the searches of the
Higgs boson decaying into bottom quarks at the Large Hadron Collider is rather
small

### Separation of soft and collinear infrared limits of QCD squared matrix elements

We present a simple way of separating the overlap between the soft and collinear factorization formulae of QCD squared matrix elements. We check its validity explicitly for single and double unresolved emissions of tree-level processes. The new method makes possible the definition of helicity-dependent subtraction terms for regularizing the real contributions in computing radiative corrections to QCD jet cross sections. This implies application of Monte Carlo helicity summation in computing higher order corrections

### Neutrino Splitting for Lorentz-Violating Neutrinos: Detailed Analysis

Lorentz-violating neutrino parameters have been severely constrained on the basis of astrophysical considerations. In the high-energy limit, one generally assumes a superluminal dispersion relation of an incoming neutrino of the form Eâ‰ˆ |p âƒ—|v , where E is the energy, p âƒ— is the momentum and v â‚Œ âˆš(1+ Î´) \u3e 1. Lepton-pair creation due to a Cerenkov-radiation-like process (Î½ â†’ Î½ + Ðµ-+e+) becomes possible above a certain energy threshold, and bounds on the Lorentz-violating parameter Î´ can be derived. Here, we investigate a related process, Î½iâ†’ Î½i+ Î½f+ Î½ â€¾f, where Î½i is an incoming neutrino mass eigenstate, while Î½f is the final neutrino mass eigenstate, with a superluminal velocity that is slightly slower than that of the initial state. This process is kinematically allowed if the Lorentz-violating parameters at high energy differ for the different neutrino mass eigenstates. Neutrino splitting is not subject to any significant energy threshold condition and could yield quite a substantial contribution to decay and energy loss processes at high energy, even if the differential Lorentz violation among neutrino flavors is severely constrained by other experiments. We also discuss the SU(2)L-gauge invariance of the superluminal models and briefly discuss the use of a generalized vierbein formalism in the formulation of the Lorentz-violating Dirac equation

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