1,720,991 research outputs found
Two-loop master integrals for a planar topology contributing to p p → tt̄ j
Full text linkWe report on recent progress for the QCD corrections to top quark pair plus jet production. In particular, we discuss a recent computation for the two-loop master integrals associated to a two-loop five-point pentagon-box integral configuration with one internal massive propagator, that contributes to top quark pair production in association with a jet in the QCD planar limit
Two-loop master integrals for the planar QCD massive corrections to di-photon and di-jet hadro-production
Full text linkAbstract We present the analytic calculation of the Master Integrals necessary to compute the planar massive QCD corrections to Di-photon (and Di-jet) production at hadron colliders. The master integrals are evaluated by means of the differential equations method and expressed in terms of multiple polylogarithms and one- or two-fold integrals of polylogarithms and irrational functions, up to transcendentality four
Two-loop amplitude for mixed QCD-EW corrections to gg → Hg
No full textWe report on the two-loop amplitude computation for the mixed QCD-electroweak corrections to the process gg → Hg, with exact dependence on the electroweak boson masses. This amplitude has been employed in the computation of next-to-leading order (NLO) mixed QCD-electroweak corrections to the Higgs-boson production rate in [47]. The master integrals that appear in the amplitude are evaluated by means of generalized power series expansions, which allows for fast and high-precision numerical evaluation of the amplitude in the physical phase-space, proving to be a powerful tool for phenomenological applications
OPE and a low-energy theorem in QCD-like theories
No full textAbstract We verify, both perturbatively and nonperturbatively asymptotically in the ultraviolet (UV), a special case of a low-energy theorem of the NSVZ type in QCD-like theories, recently derived in Phys. Rev. D 95 (2017) 054010, that relates the logarithmic derivative with respect to the gauge coupling, or the logarithmic derivative with respect to the renormalization-group (RG) invariant scale, of an n-point correlator of local operators in one side to an n + 1-point correlator with the insertion of TrF 2 at zero momentum in the other side. Our computation involves the operator product expansion (OPE) of the scalar glueball operator, TrF 2, in massless QCD, worked out perturbatively in JHEP 12 (2012) 119 — and in its RG-improved form in the present paper — by means of which we extract both the perturbative divergences and the nonperturbative UV asymptotics in both sides. We also discuss the role of the contact terms in the OPE, both finite and divergent, discovered some years ago in JHEP 12 (2012) 119, in relation to the low-energy theorem. Besides, working the other way around by assuming the low-energy theorem for any 2-point correlator of a multiplicatively renormalizable gauge-invariant operator, we compute in a massless QCD-like theory the corresponding perturbative OPE to the order of g 2 and nonperturbative asymptotics. The low-energy theorem has a number of applications: to the renormalization in asymptotically free QCD-like theories, both perturbatively and nonperturbatively in the large-N ’t Hooft and Veneziano expansions, and to the way the open/closed string duality may or may not be realized in the would-be solution by canonical string theories for QCD-like theories, both perturbatively and in the ’t Hooft large-N expansion. Our computations will also enter further developments based on the low-energy theorem
Operator mixing in massless QCD-like theories and Poincare'-Dulac theorem
Full text linkRecently, a geometric approach to operator mixing in massless QCD-like
theories -- that involves canonical forms based on the Poincare'-Dulac theorem
for the linear system that defines the renormalized mixing matrix in the
coordinate representation -- has been advocated in arXiv:2103.15527
. As a consequence, a classification of operator mixing in four cases --
depending on the canonical forms of , with
the matrix of the anomalous dimensions and
the beta function -- has been proposed: (I)
nonresonant diagonalizable, (II) resonant
diagonalizable, (III) nonresonant
nondiagonalizable, (IV) resonant
nondiagonalizable. In particular, in
arXiv:2103.15527 a detailed analysis of the case (I) -- where operator mixing
reduces to all orders of perturbation theory to the multiplicatively
renormalizable case -- has been provided. In the present paper, following the
aforementioned approach, we work out in the remaining three cases the canonical
forms for to all orders of perturbation theory,
the corresponding UV asymptotics of , and the physics interpretation.
We also work out in detail physical realizations of the cases (I) and (II).Comment: 35 pages, formulas unchanged, but some comments on the UV asymptotics
corrected, physical realizations of the resonant case and new references
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Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Experimental damage detection on small wind turbines through vibration and acoustic analysis
No full textDynamical control system optimization and noise and vibration mitigation are particularly pressing issues as regards horizontal-axis small wind turbines. A peculiarity of this technology is that the generator constitutes a non-negligible fraction of the total mass and therefore the electromechanical coupling is relevant. Condition monitoring of small wind turbine generators is an overlooked topic in the literature and in the operation of these systems. This work is devoted to damage diagnosis on a permanent magnet generator of a horizontal-axis wind turbine having 3 kW of maximum power and 2 meters of rotor diameter. The experimental analysis is conducted through wind tunnel tests and on a generator test rig where a damaged and an undamaged generators have been driven at different rotational speeds. The test rig data are useful for studying the low-frequency tail of the spectrum, where the characteristic frequencies of the bearing are located. A fault in the cage of the bearing supporting the generator is diagnosed using the spectral coherence analysis
Two-loop master integrals for pseudo-scalar quarkonium and leptonium production and decay
No full textWe compute the master integrals relevant for the two-loop corrections to pseudo-scalar quarkonium and leptonium production and decay. We present both analytic and high-precision numerical results. The analytic expressions are given in terms of multiple polylogarithms (MPLs), elliptic multiple polylogarithms (eMPLs) and iterated integrals of Eisenstein series. As an application of our results, we obtain for the first time an analytic expression for the two-loop amplitude for para-positronium decay to two photons at two loops
Two-loop form factors for pseudo-scalar quarkonium production and decay
No full textWe present the analytic expressions for the two-loop form factors for the production or decay of pseudo-scalar quarkonia, in a scheme where the quarks are produced at threshold. We consider the two-loop amplitude for the process γγ↔S0[1]1, that was previously known only numerically, as well as for the processes gg↔S0[1]1, γg↔S0[8]1 and gg↔S0[8]1, which have not been computed before. The two-loop corrections to gg↔S0[1]1 are the last missing ingredients for a full NNLO calculation of ηQ hadro-production. We discuss how the singularity structure of the amplitudes is affected by the threshold kinematics, which in particular introduces Coulomb singularities. In this context, we first show how the usual structure of the infrared singularities degenerates at threshold kinematics, and then extract the anomalous dimensions governing the Coulomb singularities for colour-singlet and octet channels, the latter being presented here for the first time. We give high-precision numerical results for the hard functions, which can be used for phenomenological studies of ηQ production and decay at NNLO
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