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Different sets of electroweak input parameters are discussed for SMEFT predictions at the LHC. The {Gmu,mZ,mW} one is presently recommended., Comment: LHC EFT WG note, 5 pages

We construct predictions for top quark pair differential distributions at hadron colliders that combine state-of-the-art NNLO QCD calculations with double resummation at NNLL' accuracy of threshold logarithms arising from soft gluon emissions and of small mass logarithms. This is the first time a resummed calculation at full NNLO+NNLL' accuracy in QCD for a process with non-trivial color structure has been completed at the differential level. Of main interest to us is the stability of the M_{tt} and top-quark p_T distributions in the boosted regime where fixed order calculations may become strongly dependent on the choice of dynamic scales. With the help of numeric and analytic arguments we confirm that the choice for the factorization and renormalization scales advocated recently by some of the authors is indeed optimal. We further derive a set of optimized kinematics-dependent scales for the matching functions which appear in the resummed calculations. Our NNLO+NNLL' prediction for the top-pair invariant mass is significantly less sensitive to the choice of factorization scale than the fixed order prediction, even at NNLO. Notably, the resummed and fixed order calculations are in nearly perfect agreement with each other in the full M_{tt} range when the optimal dynamic scale is used. For the top-quark p_T distribution the resummation performed here has less of an impact and instead we find that upgrading the matching with fixed-order from NLO+NNLL' to NNLO+NNLL' to be an important effect, a point to be kept in mind when using NLO-based Monte Carlo event generators to calculate this distribution., Comment: 45 pages, 12 figures, 2 tables. Updated formatting and included a new appendix. Matches journal version

We study the resummation of soft gluon emission corrections to the production of a top-antitop pair in association with a Z boson at the Large Hadron Collider to next-to-next-to-leading logarithmic accuracy. By means of an in-house parton level Monte Carlo code we evaluate the resummation formula for the total cross section and several differential distributions at a center-of-mass energy of 13 TeV, and we match these calculations to next-to-leading order results., Comment: 21 pages, 7 figures. arXiv admin note: text overlap with arXiv:1611.00049

We study the resummation of soft gluon emission corrections to the production of a top-antitop pair in association with a Higgs boson at the Large Hadron Collider. Starting from a soft-gluon resummation formula derived in previous work, we develop a bespoke parton-level Monte Carlo program which can be used to calculate the total cross section along with differential distributions. We use this tool to study the phenomenological impact of the resummation to next-to-next-to-leading logarithmic (NNLL) accuracy, finding that these corrections increase the total cross section and the differential distributions with respect to NLO calculations of the same observables., Comment: 26 pages, 9 figures. A few typos and an incorrect reference were fixed

We consider soft gluon emission corrections to the production of a top-antitop pair in association with a W boson at the Large Hadron Collider. We obtain a soft-gluon resummation formula for this production process which is valid up to next-to-next-to-leading logarithmic accuracy. We evaluate the soft gluon resummation formula in Mellin space by means of an in-house parton level Monte Carlo code which allows us to obtain predictions for the total cross section as well as for several differential distributions. We study the impact of the soft-gluon resummation corrections in comparison to fixed order calculations., Comment: 31 pages, 8 figures and 5 tables

We consider soft gluon emission corrections to the production of a top-antitop pair in association with a Higgs boson at hadron colliders. In particular, we present a soft-gluon resummation formula for this production process and gather all elements needed to evaluate it at next-to-next-to-leading logarithmic order. We employ these results to obtain approximate next-to-next-to-leading order (NNLO) formulas, and implement them in a bespoke parton-level Monte Carlo program which can be used to calculate the total cross section along with arbitrary differential distributions. We use this tool to study the phenomenological impact of the approximate NNLO corrections, finding that they increase the total cross section and the differential distributions which we evaluated in this work., Comment: 35 pages, 5 tables and 12 figures. Version published in JHEP 1603 (2016) 124

The LHCb collaboration has recently performed a first measurement of the angular production asymmetry in the distribution of beauty quarks and anti-quarks at a hadron collider. We calculate the corresponding standard model prediction for this asymmetry at fixed-order in perturbation theory. Our results show good agreement with the data, which is provided differentially for three bins in the invariant mass of the $b \bar b$ system. We also present similar predictions for both beauty-quark and charm-quark final states within the LHCb acceptance for a collision energy of $\sqrt{s} = 13 \, {\rm TeV}$. We finally point out that a measurement of the ratio of the $b \bar b$ and $c \bar c$ cross sections may be useful for experimentally validating charm-tagging efficiencies., Comment: 4.5 pages + references, 1 figure, 4 tables

We derive the hard functions for all 2->2 processes in massless QCD up to next-to-next-to-leading order (NNLO) in the strong coupling constant. By employing the known one- and two-loop helicity amplitudes for these processes, we obtain analytic expressions for the ultraviolet and infrared finite, minimally subtracted hard functions, which are matrices in color space. These hard functions will be useful in carrying out higher-order resummations in processes such as dijet and highly energetic top-quark pair production by means of soft-collinear effective theory methods., Comment: 20 pages

We review a Soft Collinear Effective Theory approach to the study of factorization and resummation of QCD effects in top-quark pair production. In particular, we consider differential cross sections such as the top-quark pair invariant mass distribution and the top-quark transverse momentum and rapidity distributions. Furthermore, we focus our attention on the large invariant mass and large transverse momentum kinematic regions, characteristic of boosted top quarks. We discuss the factorization of the differential cross section in the double soft gluon emission and small top-quark mass limit, both in Pair Invariant Mass (PIM) and One Particle Inclusive (1PI) kinematics. The factorization formulas can be employed in order to implement the simultaneous resummation of soft emission and small mass effects up to next-to-next-to-leading logarithmic accuracy. The results are also used to construct improved next-to-next-to-leading order approximations for the differential cross sections., Comment: 6 pages. Proceedings of the Second Annual Conference on Large Hadron Collider Physics (LHCP 2014), Columbia University, New York, June 2-7, 2014

Motivated by the recent measurement of the dimuon asymmetry by the D{\O} collaboration, which could be interpreted as an enhanced decay rate difference in the neutral $B_d$-meson system, we investigate the possible size of new-physics contributions to $\Delta \Gamma_d$. In particular, we perform model-independent studies of non-standard effects associated to the dimension-six current-current operators $(\bar{d} p)(\bar p^{\hspace{0.25mm}\prime} b)$ with $p,p^\prime= u,c$ as well as $(\bar{d}b) (\bar\tau\tau)$. In both cases we find that for certain flavour or Lorentz structures of the operators sizable deviations of $\Delta \Gamma_d$ away from the Standard Model expectation cannot be excluded in a model-independent fashion., Comment: 35 pages, 14 figures. Equation (5.10) corrected, references added. Conclusions remain unchanged

We study single-particle inclusive (1PI) distributions in top-quark pair production at hadron colliders, working in the highly boosted regime where the top-quark p_T is much larger than its mass. In particular, we derive a novel factorization formula valid in the small-mass and soft limits of the differential partonic cross section. This provides a framework for the simultaneous resummation of soft gluon corrections and small-mass logarithms, and also an efficient means of obtaining higher-order corrections to the differential cross section in this limit. The result involves five distinct one-scale functions, three of which arise through the subfactorization of soft real radiation in the small-mass limit. We list the NNLO corrections to each of these functions, building on results in the literature by performing a new calculation of a soft function involving four light-like Wilson lines to this order. We thus obtain a nearly complete description of the small-mass limit of the differential partonic cross section at NNLO near threshold, missing only terms involving closed top-quark loops in the virtual corrections., Comment: 36 pages

We obtain a soft plus virtual approximation to the NNLO QCD contributions to the top-pair invariant mass distribution at hadron colliders. It is valid up to corrections of order m_t^2/M^2, with M the pair invariant mass. This is currently the most complete QCD calculation for a differential cross section in top-quark pair production, and is useful for describing the high invariant mass region characteristic of boosted top quarks. We use our results to construct an improved NNLO approximation for the pair invariant mass distribution and compare it with previous, less complete approximations based on logarithmic terms from NNLL soft-gluon resummation alone. We find that the new NNLO approximation produces moderate enhancements of the differential cross section compared to previous ones, the effect being slightly more important at low values of invariant mass than at high ones. On the other hand, at high values of invariant mass the new NNLO corrections are dominated by even higher-order effects included in NNLL soft-gluon resummation, reaffirming the need for resummation in describing the highly boosted regime., Comment: 23 pages, 5 tables, 1 figure; version published in JHEP

At high values of the pair invariant mass the differential cross section for top-quark pair production at hadron colliders factorizes into soft, hard, and fragmentation functions. In this paper we calculate the next-to-next-to-leading-order (NNLO) corrections to the soft function appearing in this factorization formula, thus providing the final piece needed to evaluate at NNLO the differential cross section in the virtual plus soft approximation in the large invariant-mass limit. Technically, this amounts to evaluating the vacuum expectation value of a soft Wilson loop operator built out of light-like Wilson lines for each of the four partons participating in the hard scattering process, with a certain constraint on the total energy of the soft radiation. Our result turns out to be surprisingly simple, because in the sum of all graphs the three and four parton contributions multiply color structures whose coefficients are governed by the non-abelian exponentiation theorem., Comment: 18 pages main text, 11 pages appendix

We investigate the production of highly energetic top-quark pairs at hadron colliders, focusing on the case where the invariant mass of the pair is much larger than the mass of the top quark. In particular, we set up a factorization formalism appropriate for describing the differential partonic cross section in the double soft and small-mass limit, and explain how to resum simultaneously logarithmic corrections arising from soft gluon emission and from the ratio of the pair-invariant mass to that of the top quark to next-to-next-to-leading logarithmic accuracy. We explore the implications of our results on approximate next-to-next-to-leading order formulas for the differential cross section in the soft limit, pointing out that they offer a simplified calculational procedure for determining the currently unknown delta-function terms in the limit of high invariant mass., Comment: 32 pages

We review theoretical calculations for top-quark production that include complete next-to-leading-order QCD corrections as well as higher-order soft-gluon corrections from threshold resummation. We discuss in detail the differences between various approaches that have appeared in the literature and review results for top-quark total cross sections and differential distributions at the Tevatron and the LHC., Comment: 35 pages, 10 figures; invited review for a special "Top and flavor physics in the LHC era" issue of the European Physical Journal C

We review the progress on the determination of the CKM matrix elements |V_cs|, |V_cd|, |V_cb|, |V_ub| and heavy quark masses presented at the 6th International Workshop on the CKM Unitarity Triangle., Comment: Proceedings of CKM2010, the 6th International Workshop on the CKM Unitarity Triangle, University of Warwick, UK, 6-10 September 2010. Reference added

We make use of recent results in effective theory and higher-order perturbative calculations to improve the theoretical predictions of the QCD contribution to the top-quark pair production forward-backward asymmetry at the Tevatron. In particular, we supplement the fixed-order NLO calculation with higher-order corrections from soft gluon resummation at NNLL accuracy performed in two different kinematic schemes, which allows us to make improved predictions for the asymmetry in the $p\bar p$ and $t\bar t$ rest frames as a function of the rapidity and invariant mass of the $t\bar t$ pair. Furthermore, we provide binned results which can be compared with the recent measurements of the forward-backward asymmetry in events with a large pair invariant mass or rapidity difference. Finally, we calculate at NLO+NNLL order the top-quark charge asymmetry at the LHC as a function of a lower rapidity cut-off for the top and antitop quarks., Comment: 12 pages, 6 figures, 4 tables

We make use of recent results in effective theory and higher-order perturbative calculations to improve the theoretical predictions of the top-quark pair production cross section at hadron colliders. In particular, we supplement the fixed-order NLO calculation with higher-order corrections from soft gluon resummation at NNLL accuracy. Uncertainties due to power corrections to the soft limit are estimated by combining results from single-particle inclusive and pair invariant-mass kinematics. We present our predictions as functions of the top-quark mass in both the pole scheme and the MS(bar) scheme. We also discuss the merits of using threshold masses as an alternative, and calculate the cross section with the top-quark mass defined in the 1S scheme as an illustrative example., Comment: 9 pages

Precision predictions for phenomenologically interesting observables such as the t-tbar invariant mass distribution and forward-backward asymmetry in top-quark pair production at hadron colliders require control over the differential cross section in perturbative QCD. In this paper we improve existing calculations of the doubly differential cross section in the invariant mass and scattering angle by using techniques from soft-collinear effective theory to perform an NNLL resummation of threshold logarithms, which become large when the invariant mass M of the top-quark pair approaches the partonic center-of-mass energy. We also derive an approximate formula for the differential cross section at NNLO in fixed-order perturbation theory, which completely determines the coefficients multiplying the singular plus distributions. We then match our results in the threshold region with the exact results at NLO in fixed-order perturbation theory, and perform a numerical analysis of the invariant mass distribution, the total cross section, and the forward-backward asymmetry. We argue that these are the most accurate predictions available for these observables at present. Using MSTW2008NNLO parton distribution functions (PDFs) along with \alpha_s(M_Z)=0.117 and m_t=173.1 GeV, we obtain for the inclusive production cross sections at the Tevatron and LHC the values \sigma_{Tevatron} = (6.30 +-0.19 +0.31-0.23) pb and \sigma_{LHC} = (149 +- 7 +- 8) pb, where the first error results from scale variations while the second reflects PDF uncertainties., Comment: 61 pages, 18 figures, version to appear in JHEP

We calculate the leading O(alpha_s^4) contributions to the invariant mass distribution of top-quark pairs produced at the Tevatron and LHC, in the limit where the invariant mass of the t-tbar pair approaches the partonic center-of-mass energy. Our results determine at NNLO in alpha_s the coefficients of all singular plus distributions and scale-dependent logarithms in the differential partonic cross sections for q-qbar, gg -> t-tbar + X. A numerical analysis showing the effects of the NNLO corrections on the central values and scale dependence of the invariant mass distribution is performed. The NNLO corrections are found to significantly enhance the cross section and reduce the perturbative uncertainties compared to the NLO calculation., Comment: 14 pages, 4 figures. Version published in Physics Letters B. Mathematica package updated.

The infrared divergences of QCD scattering amplitudes can be derived from an anomalous dimension \Gamma, which is a matrix in color space and depends on the momenta and masses of the external partons. It has recently been shown that in cases where there are at least two massive partons involved in the scattering process, starting at two-loop order \Gamma receives contributions involving color and momentum correlations between three (and more) partons. The three-parton correlations can be described by two universal functions F_1 and f_2. In this paper these functions are calculated at two-loop order in closed analytic form and their properties are studied in detail. Both functions are found to be suppressed like O(m^4/s^2) in the limit of small parton masses, in accordance with mass factorization theorems proposed in the literature. On the other hand, both functions are O(1) and even diverge logarithmically near the threshold for pair production of two heavy particles. As an application, we calculate the infrared poles in the q qbar --> t tbar and g g --> t tbar scattering amplitudes at two-loop order., Comment: 27 pages, 2 figures, includes 3 Mathematica files; v2: bug in one of the Mathematica files fixed, minor changes in the first four lines of Table 1

We complete the study of two-loop infrared singularities of scattering amplitudes with an arbitrary number of massive and massless partons in non-abelian gauge theories. To this end, we calculate the universal functions F_1 and f_2, which completely specify the structure of three-parton correlations in the soft anomalous-dimension matrix, at two-loop order in closed analytic form. Both functions are found to be suppressed like O(m^4/s^2) in the limit of small parton masses, in accordance with mass factorization theorems proposed in the literature. On the other hand, they are unsuppressed and diverge logarithmically near the threshold for pair production of two heavy particles. As an application, we calculate the two-loop anomalous-dimension matrix for q q_bar --> t t_bar near threshold and show that it is not diagonal in the s-channel singlet-octet basis., Comment: 4 pages, 1 figure

The calculation of partial decay rates in B --> X_u l nu decays at next-to-next-to-leading order (NNLO) in alpha_s and to leading order in 1/m_b is described. New results for the hard function are combined with known results for the jet function and shape-function moments in a numerical analysis which explores the impact of the NNLO corrections on partial decay rates and the determination of |V_{ub}|., Comment: Talk given at the 34th International Conference on High Energy Physics, Philadelphia, July 2008

I briefly review the theory status of exclusive rare radiative decays., Comment: Talk given at Flavor Physics & CP Violation Conference, Taipei, 2008

We compute NNLO (${\cal O}(\alpha_s^2)$) corrections to the hard-scattering kernels entering the QCD factorization formula for $B\to V\gamma$ decays, where $V$ is a light vector meson. We give complete NNLO results for the dipole operators $Q_7$ and $Q_8$, and partial results for $Q_1$ valid in the large-$\beta_0$ limit and neglecting the NNLO correction from hard spectator scattering. Large perturbative logarithms in the hard-scattering kernels are identified and resummed using soft-collinear effective theory. We use our results to estimate the branching fractions for $B\to K^*\gamma$ and $B_s\to \phi\gamma$ decays at NNLO and compare them with the current experimental data., Comment: 33 pages, 2 figures; text modified in sections 3 and 4, added 3 equations [(23),(40),(46)] and corrected Eq. (39); added 4 references; title slightly modified; to appear in the European Physical Journal C

Renormalization-group methods in soft-collinear effective theory are used to perform the resummation of large perturbative logarithms for deep-inelastic scattering in the threshold region x->1. The factorization theorem for the structure function F_2(x,Q^2) for x->1 is rederived in the effective theory, whereby contributions from the hard scale Q^2 and the jet scale Q^2(1-x) are encoded in Wilson coefficients of effective-theory operators. Resummation is achieved by solving the evolution equations for these operators. Simple analytic results for the resummed expressions are obtained directly in momentum space, and are free of the Landau-pole singularities inherent to the traditional moment-space results. We show analytically that the two methods are nonetheless equivalent order by order in the perturbative expansion, and perform a numerical comparison up to next-to-next-to-leading order in renormalization-group improved perturbation theory., Comment: 39 pages, 9 figures

We use soft-collinear effective theory (SCET) to study the factorization properties of deep inelastic scattering in the region of phase space where 1-x = O(Lambda_{QCD/Q}). By applying a regions analysis to loop diagrams in the Breit frame, we show that the appropriate version of SCET includes anti-hard-collinear, collinear, and soft-collinear fields. We find that the effects of the soft-collinear fields spoil perturbative factorization even at leading order in the 1/Q expansion., Comment: 22 pages, 4 figures. Reference added, other small changes for journal version

The renormalon calculus is used to calculate the terms of order $\beta_0^{n-1}\alpha_s^n$ in the perturbative expansions of the Wilson coefficients and hard-scattering kernels entering the QCD factorization formula for hadronic B-meson decays into two light pseudoscalar mesons. The asymptotic behavior of the expansions is analyzed, and a minimal model of power corrections arising from soft ``non-factorizable'' gluon exchange to the B->pi K,pi pi decay amplitudes is obtained, which takes into account the structure of the leading and subleading infrared renormalon singularities. Whereas the resulting power corrections are generally very small, some of the strong-interaction phases of the hard-scattering kernels receive sizeable two-loop corrections. The implications of these findings on CP asymmetries and branching ratios are investigated., Comment: 19 pages, 2 figures, journal version published in JHEP

Using the renormalon calculus, we study the asymptotic behavior of the perturbative expansion of the hard-scattering kernels entering the QCD factorization formula for the nonleptonic weak decays B->D M, where M is a light meson. In the ``large-beta_0 limit'', the kernels are infrared finite and free of endpoint singularities to all orders of perturbation theory. The leading infrared renormalon singularity corresponding to a power correction of order Lambda/m_b vanishes if the light meson has a symmetric light-cone distribution amplitude. We calculate the Borel transforms and the corresponding momentum distribution functions of the hard-scattering kernels, and resum the series of O(beta_0^{n-1} alpha_s^n) corrections to explore the numerical significance of higher-order perturbative and power corrections. We also derive explicit expressions for the O(beta_0 alpha_s^2) contributions to the kernels, and for the renormalon singularities corresponding to power corrections of order (Lambda/m_b)^2. Finally, we study the limit m_c->0 relevant to charmless hadronic decays such as B->pi pi., Comment: 27 pages, 4 figures