2,122 research outputs found

### Virtual amplitudes and threshold behaviour of hadronic top-quark pair-production cross sections

We present the two-loop virtual amplitudes for the production of a top-quark pair in gluon fusion. The evaluation method is based on a numerical solution of differential equations for master integrals in function of the quark velocity and scattering angle starting from a boundary at high-energy. The results are given for the renormalized infrared finite remainders on a large grid and have recently been used in the calculation of the total cross sections at the next-to-next-to-leading order. For convenience, we also give the known results for the quark annihilation case on the same grid. Outside of the kinematical range covered by the grid, we provide threshold and high-energy expansions

### The soft function for color octet production at threshold

We evaluate the next-to-next-to-leading order soft function for the production of a massive color octet state at rest in the collision of two massless colored partons in either the fundamental or the adjoint representation. The main application of our result is the determination of the threshold expansion of the heavy-quark pair-production cross sections in the quark annihilation and gluon fusion channels. We discuss the factorization necessary for this purpose and explain the relationship between hard functions and virtual amplitudes

### Matching the Nagy-Soper parton shower at next-to-leading order

We present an Mc@Nlo-like matching of next-to-leading order QCD calculations with the Nagy-Soper parton shower. An implementation of the algorithm within the Helac-Dipoles Monte Carlo generator is used to address the uncertainties and ambiguities of the matching scheme. First results obtained using the Nagy-Soper parton shower implementation in Deductor in conjunction with the Helac-Nlo framework are given for the pp â†’ t t Â¯ j + X $pp\to t\overline{t}j+X$ process at the LHC with s = 8 $\sqrt{s}=8$ TeV. Effects of resummation are discussed for various observables

### Higgs boson to di-tau channel in chargino-neutralino searches at the LHC

We consider chargino-neutralino production, Ï‡ Ëœ 2 0 Ï‡ Ëœ 1 Â± â†’ h Ï‡ Ëœ 1 0 W Â± Ï‡ Ëœ 1 0 ${\tilde{\chi}}_2^0{\tilde{\chi}}_1^{\pm}\to \left(h{\tilde{\chi}}_1^0\right)\left({W}^{\pm }{\tilde{\chi}}_1^0\right)$ , which results in Higgs boson final states that subsequently decay (inclusively) to leptons (either h â†’ Ï„ + Ï„ âˆ’ or h â†’ W + W âˆ’ â†’ ( e + e âˆ’ ,Î¼ + Î¼ âˆ’ ,Ï„ + Ï„ âˆ’ )+ T ). Such channels are dominant in large regions of the allowed supersymmetric parameter space for many concrete supersymmetric models. The existence of leptons allows for good control over the backgrounds, rendering this channel competitive to the conventional h â†’ b b Â¯ $b\overline{b}$ channel. We include hadronic decays of the Ï„ leptons in our analysis through a Ï„ -identification algorithm. We consider integrated luminosities of 100 fb âˆ’1 , 300 fb âˆ’1 and 3000 fb âˆ’1 , for an LHC running at pp centre-of-mass energy of 14 TeV and provide the expected constraints on the M 2 - M 1 plane

### Comparing EFT and exact one-loop analyses of non-degenerate stops

We develop a universal approach to the one-loop effective field theory (EFT) using the Covariant Derivative Expansion (CDE) method. We generalise previous results to include broader classes of UV models, showing how expressions previously obtained assuming degenerate heavy-particle masses can be extended to non-degenerate cases. We apply our method to the general MSSM with non-degenerate stop squarks, illustrating our approach with calculations of the coefficients of dimension-6 operators contributing to the hgg and hÎ³Î³ couplings, and comparing with exact calculations of one-loop Feynman diagrams. We then use present and projected future sensitivities to these operator coefficients to obtain present and possible future indirect constraints on stop masses. The current sensitivity is already comparable to that of direct LHC searches, and future FCC-ee measurements could be sensitive to stop masses above a TeV. The universality of our one-loop EFT approach facilitates extending these constraints to a broader class of UV models

### Lattice QCD

A general introduction to lattice QCD suitable for graduate students in
experimental and theoretical particle physics. Aimed at those who want to know
how lattice calculations are done, and what the pitfalls are, without having to
do the calculations themselves.Comment: Lectures given at 55th Scottish Universities Summer School, St
Andrews, August 200

### Physics of Binary Information

Basic concepts of theoretical particle physics, including quantum mechanics
and Poincar\'e invariance, the leptonic mass spectrum and the proton mass, can
be derived, without reference to first principles, from intrinsic properties of
the simplest elements of information represented by binary data. What we
comprehend as physical reality is, therefore, a reflection of mathematically
determined logical structures, built from elements of binary data.Comment: 8 page

### The Charm of Theoretical Physics (1958-1993)

Personal recollections on theoretical particle physics in the years when the
Standard Theory was formed. In the background, the remarkable development of
Italian theoretical physics in the second part of the last century, with great
personalities like Bruno Touschek, Raoul Gatto, Nicola Cabibbo and their
schools.Comment: 53 pages, 12 figures, to be published in The European Physical
Journal H. New version with added text and figure

### The Future of U.S. Particle Theory: Report of the DPF Theory Panel

This report summarizes the findings of the DPF Theory Panel which was formed
with a goal of understanding the scientific problems and opportunities of the
next decade, as well as the challenges involved in sustaining a first-class
program in theoretical particle physics research in the United States.Comment: 23 pages, LaTeX, Chapter 5 of the report "Planning the Future of U.S.
Particle Physics (Snowmass 2013)

### Computer Algebra in Particle Physics

These lectures given to graduate students in theoretical particle physics,
provide an introduction to the ``inner workings'' of computer algebra systems.
Computer algebra has become an indispensable tool for precision calculations in
particle physics. A good knowledge of the basics of computer algebra systems
allows one to exploit these systems more efficiently.Comment: 56 pages, lectures given at the "Seminario Nazionale di Fisica
Teorica", Parma, September 200

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