Precision top pair production at hadron colliders

We demonstrate the impact of recent NNLO calculations on precision top quark phenomenology.Comment: Based on talks given at the 11th DESY Workshop "Loops and Legs in Quantum Field Theory 2012", the 7th International Workshop on the CKM Unitarity Triangle "CKM 2012" and the 5th International Workshop on Top Quark Physics "Top 2012

Determination of the top quark mass from leptonic observables

We present a procedure for the determination of the mass of the top quark at the LHC based on leptonic observables in dilepton $t\bar{t}$ events. Our approach utilises the shapes of kinematic distributions through their few lowest Mellin moments; it is notable for its minimal sensitivity to the modelling of long-distance effects, for not requiring the reconstruction of top quarks, and for having a competitive precision, with theory errors on the extracted top mass of the order of 0.8 GeV. A novel aspect of our work is the study of theoretical biases that might influence in a dramatic way the determination of the top mass, and which are potentially relevant to all template-based methods. We propose a comprehensive strategy that helps minimise the impact of such biases, and leads to a reliable top mass extraction at hadron colliders.Comment: 29 pages, 3 figure

Final state interactions in single- and multi-particle inclusive cross sections for hadronic collisions

We study the role of low momentum transfer (soft) interactions between high-transverse momentum heavy particles and beam remnants (spectators) in hadronic collisions. Such final-state interactions are power suppressed for single-particle inclusive cross sections whenever that particle is accompanied by a recoiling high-p_T partner whose momentum is not fixed. An example is the single-top inclusive cross section in top pair production. Final-state soft interactions in multi-particle inclusive cross sections, including transverse momentum distributions, however, produce leading power corrections in the absence of hard recoiling radiation. Nonperturbative corrections due to scattering from spectators are generically suppressed by powers of \Lambda/p'_T, where \Lambda is a hadronic scale, and p'_T is the largest transverse momentum of radiation recoiling against the particles whose momenta are observed.Comment: 18 pages, 6 figure

A Fused Elastic Net Logistic Regression Model for Multi-Task Binary Classification

Multi-task learning has shown to significantly enhance the performance of multiple related learning tasks in a variety of situations. We present the fused logistic regression, a sparse multi-task learning approach for binary classification. Specifically, we introduce sparsity inducing penalties over parameter differences of related logistic regression models to encode similarity across related tasks. The resulting joint learning task is cast into a form that lends itself to be efficiently optimized with a recursive variant of the alternating direction method of multipliers. We show results on synthetic data and describe the regime of settings where our multi-task approach achieves significant improvements over the single task learning approach and discuss the implications on applying the fused logistic regression in different real world settings.Comment: 17 page

Top++: a program for the calculation of the top-pair cross-section at hadron colliders

We present the program Top++ for the numerical evaluation of the total inclusive cross-section for producing top quark pairs at hadron colliders. The program calculates the cross-section in a) fixed order approach with exact next-to-next-to leading order (NNLO) accuracy and b) by including soft-gluon resummation for the hadronic cross-section in Mellin space with full next-to-next-to-leading logarithmic (NNLL) accuracy. The program offers the user significant flexibility through the large number (29) of available options. Top++ is written in C++. It has a very simple to use interface that is intuitive and directly reflects the physics. The running of the program requires no programing experience from the user.Comment: v2.0: Major update: includes full NNLO result; functionality updates. Program webpage: http://www.alexandermitov.com/softwar

NNLO corrections to top pair production at hadron colliders: the quark-gluon reaction

We compute the next-to-next-to-leading order QCD correction to the total inclusive top pair production cross-section in the reaction qg \to t\bar t + X. We find moderate O(1%) correction to central values at both Tevatron and LHC. The scale variation of the cross-section remains unchanged at the Tevatron and is significantly reduced at the LHC. We find that recently introduced approximation based on the high-energy limit of the top pair cross-section significantly deviates from the exact result. The results derived in the present work are included in version 1.4 of the program Top++. Work towards computing the reaction gg\to t\bar t+X is ongoing.Comment: 17+1 pages, 6 figure

Option Pricing by Branching Process

2000 Mathematics Subject Classification: 60J80, 62P05.The randomly indexed Galton-Watson branching process has been used for the model of daily stock prices. Using this stock price process we derive a new formula for the price of European call options.This paper is partially supported by NSF of Bulgaria, Grant No VU-MI-105/2005

NNLO splitting and coefficient functions with time-like kinematics

We discuss recent results on the three-loop (next-to-next-to-leading order, NNLO) time-like splitting functions of QCD and the two-loop (NNLO) coefficient functions in one-particle inclusive e+e- annihilation. These results form the basis for extracting fragmentation functions for light and heavy flavors with NNLO accuracy that will be needed at the LHC and ILC. The two-loop calculations have been performed in Mellin space based on a new method, the main features of which we also describe briefly.Comment: Presented by A.M. at Loops and Legs in Quantum Field Theory, 23-28 April 2006, Eisenach, German

Diagrammatic Exponentiation for Products of Wilson Lines

We provide a recursive diagrammatic prescription for the exponentiation of gauge theory amplitudes involving products of Wilson lines and loops. This construction generalizes the concept of webs, originally developed for eikonal form factors and cross sections with two eikonal lines, to general soft functions in QCD and related gauge theories. Our coordinate space arguments apply to arbitrary paths for the lines.Comment: 16 pages, 4 figures; minor corrections, version to appear in Phys. Rev.

Threshold Resummation for Top-Pair Hadroproduction to Next-to-Next-to-Leading Log

We derive the threshold-resummed total cross section for heavy quark production in hadronic collisions accurate to next-to-next-to-leading logarithm, employing recent advances on soft anomalous dimension matrices for massive pair production in the relevant kinematic limit. We also derive the relation between heavy quark threshold resummations for fixed pair kinematics and the inclusive cross section. As a check of our results, we have verified that they reproduce all poles of the color-averaged q\bar{q} -> t\bar{t} amplitudes at two loops, noting that the latter are insensitive to the color-antisymmetric terms of the soft anomalous dimension.Comment: 18 pages; Expanded discussion, added references. Results unchanged