Subtraction Scheme Research Articles

Subtraction of the tt¯ contribution in tWb¯ production at the one-loop level

The tWb¯ production contributes to the real corrections to the tW cross section. It would interfere with the top quark pair production, causing difficulties in a clear definition of the tWb¯ events. The subtraction of the tt¯ contributions has been performed in the diagram removal or diagram subtraction schemes for the tree-level processes. However, these schemes rely on the ability to identify the double resonant diagrams and thus can not be extended to loop diagrams. We propose a new scheme to subtract the tt¯ contributions by power expansion of the squared amplitude in the resonant region. In order to cancel the infra-red divergences of the loop amplitudes, a widely used method is to introduce the dipole counter-terms, an ingredient in calculations of the full next-to-leading order QCD corrections. In our scheme, these counter-terms are also power-expanded. As a proof of principle, we calculate the one-loop correction to the dd¯ → b¯Wt process, and present the invariant mass distribution of the Wb¯ system.

Complete Next-to-Leading Order QCD Corrections to ZZ Production in Gluon Fusion

We calculate the complete next-to-leading order (NLO) QCD corrections to loop-induced gg→ZZ production including full top-quark mass effects. The two-loop virtual corrections are obtained by combining analytic results for the massless, Higgs-mediated, and one-loop factorizable contributions with numerically computed amplitudes containing the top-quark mass. We show that the choice of subtraction scheme for the virtual contribution impacts the precision with which the virtual contribution must be evaluated in order to obtain sufficiently precise phenomenological predictions. For direct production through a massive top-quark loop, we observe that the relative NLO corrections are large. The direct massive and Higgs-mediated contributions individually increase relative to the massless production at high diboson invariant mass, but interfere destructively with each other. At the Large Hadron Collider, the NLO corrections to the gluon channel give a sizable contribution to the pp→ZZ+X cross section at N3LO. Published by the American Physical Society 2025

The simplest minimal subtraction for massive scalar field theory

The simplest minimal subtraction method for massive λϕ4 scalar field theory is presented. We utilize the one-particle irreducible vertex parts framework to deal only with the primitive divergent ones that can be renormalized multiplicatively. We give a unified description for spacetime metric tensor with either Minkowski or Euclidean signature. The partial-p operation in the remaining diagrams of the two-point vertex part eliminates its overlapping divergences. We show how the parametric dissociation transform effectively removes the external momentum dependence of the coefficient of the squared bare mass after performing the partial-p operation in the two-point vertex part diagrams. The resemblance of this method with a minimal subtraction scheme in the massless theory is pointed out. We derive the Callan-Symanzik equations using minimal subtraction arguments and discuss the scaling limit in the ultraviolet region. We apply the method to determine critical exponents for an O(N) internal symmetry at least up to two-loop order with a flat Euclidean metric and find perfect agreement with all previous results in the literature.

Detecting the flavor content of the vacuum using the Dirac operator spectrum

We compute the overlap Dirac spectrum on three gauge ensembles generated using 2+1-flavor domain wall fermions. The three ensembles have different lattice spacings, and two of them have quark masses tuned to the physical point. The spectral density is determined up to λ∼100 MeV with subpercentage statistical uncertainty. We find that the density is close to a constant below λ∼20 MeV as predicted by chiral perturbative theory (χPT) and then increases linearly due to the strange quark mass. By fitting to the next-to-leading order χPT form and using the nonperturbative renormalization using the regularization independent momentum subtraction scheme, the SU(2) (keeping the strange quark mass at the physical point) and SU(3) chiral condensates at MS¯ 2 GeV are determined to be Σ=(265.4(0.5)(4.2) MeV)3 and Σ0=(234.3(0.5)(25.8) MeV)3, respectively. The pion decay constants are also determined to be F=84.1(1.9)(8.0) and F0=58.6(0.5)(10.0) MeV. The systematic errors are carefully estimated including the effects of fitting ranges and the uncertainty of low-energy constant L6. We also show that one can resolve the sea flavor content of the sea quarks and constrain their masses with ∼10%–20% statistical uncertainties using the Dirac spectral density. Published by the American Physical Society 2024

Generation of non-Gaussian states of light using deterministic photon subtraction

Abstract We explore a recently demonstrated deterministic photon subtraction scheme, based on single-photon Raman interaction with a Λ-type three-level atom, as a tool for manipulating quantum state of few-photon light pulses. We establish a comprehensive theoretical framework using input–output formalism and quantum regression theorem, enabling calculation of the first order autocorrelation matrices of the output light and identification of the temporal modes present in the generated light via their eigendecomposition. By modeling the entire system as a quantum network consisting multiple virtual cavities and a lambda-type emitter cascaded in two parallel guided modes of opposite propagation directions, we extract the quantum state occupying the modes of interest. For both squeezed vacuum and coherent light input pulses, the Wigner function of the output light after photon subtraction clearly reveals its non-Gaussian character. Furthermore, we propose a measurement-based scheme on the subtracted photon which can lead to conditional generation of quantum states resembling Schrodinger’s kitten state directly from coherent input light with fidelities above 99%. This result is particularly nothworthy, as coherent pulses, unlike the squeezed vacuum inputs commonly used in previous studies, are readily available in most experimental setups.

Gauge-invariant renormalization of four-quark operators

We study the renormalization of four-quark operators in one-loop perturbation theory. We employ a coordinate-space gauge-invariant renormalization scheme (GIRS), which can be advantageous compared to other schemes, especially in nonperturbative lattice investigations. From our perturbative calculations, we extract the conversion factors between GIRS and the modified minimal subtraction scheme (MS¯) at the next-to-leading order. As a by-product, we also obtain the relevant anomalous dimensions in the GIRS scheme. A formidable issue in the study of the four-quark operators is that operators with different Dirac matrices mix among themselves upon renormalization. We focus on both parity-conserving and parity-violating four-quark operators, which change flavor numbers by two units (ΔF=2). The extraction of the conversion factors entails the calculation of two-point Green’s functions involving products of two four-quark operators, as well as three-point Green’s functions with one four-quark and two bilinear operators. The significance of our results lies in their potential to refine our understanding of QCD phenomena, offering insights into the precision of Cabibbo-Kobayashi-Maskawa (CKM) matrix elements and shedding light on the nonperturbative treatment of complex mixing patterns associated with four-quark operators. Published by the American Physical Society 2024

Impact of gauge fixing precision on the continuum limit of nonlocal quark-bilinear lattice operators

We analyze the gauge fixing precision dependence of some nonlocal quark-bilinear lattice operators interesting in computing parton physics for several measurements, using five lattice spacings ranging from 0.032 to 0.121 fm. Our results show that gauge-dependent nonlocal measurements are significantly more sensitive to the precision of gauge fixing than anticipated. The impact of imprecise gauge fixing is significant for fine lattices and long distances. For instance, even with the typically defined precision of Landau gauge fixing of 10−8, the deviation caused by imprecise gauge fixing can reach 12%, when calculating the trace of Wilson lines at 1.2 fm with a lattice spacing of approximately 0.03 fm. Similar behavior has been observed in ξ gauge and Coulomb gauge as well. For both quasi-parton-distribution functions (quasi-PDFs) and quasi-transverse-momentum-dependent PDFs operators renormalized using the regularization independent momentum subtraction (RI/MOM) scheme, convergence for different lattice spacings at long distance is only observed when the precision of Landau gauge fixing is sufficiently high. To describe these findings quantitatively, we propose an empirical formula to estimate the required precision. Published by the American Physical Society 2024

Renormalization of nonlocal gluon operators on the lattice

Wen study the renormalization of a complete set of gauge-invariant gluon nonlocal operators in lattice perturbation theory. We determine the mixing pattern under renormalization of these operators using symmetry arguments, which extend beyond perturbation theory. Additionally, we derive the renormalization factors of the operators within the modified minimal subtraction (MS¯) scheme up to one loop. To enable a nonperturbative renormalization procedure, we investigate a suitable version of the modified regularization-invariant (RI′) scheme, and we calculate the conversion factors from that scheme to MS¯. The computations are performed by employing both dimensional and lattice regularizations, using the Wilson gluon action. This work is relevant to nonperturbative studies of the gluon parton distribution functions (PDFs) on the lattice. Published by the American Physical Society 2024

Systematic improvement of x -dependent unpolarized nucleon generalized parton distributions in lattice-QCD calculation

We present a first study of the effects of renormalization-group resummation (RGR) and leading-renormalon resummation (LRR) on the systematic errors of the unpolarized isovector nucleon generalized parton distribution in the framework of large-momentum effective theory. This work is done using lattice gauge ensembles generated by the MILC Collaboration, consisting of 2+1+1 flavors of highly improved staggered quarks with a physical pion mass at lattice spacing a≈0.09 fm and a box width L≈5.76 fm. We present results for the nucleon H and E generalized parton distributions (GPDs) with average boost momentum Pz≈2 GeV at momentum transfers Q2=[0,0.97] GeV2 at skewness ξ=0 as well as Q2∈0.23 GeV2 at ξ=0.1, renormalized in the modified minimal subtraction (MS¯) scheme at scale μ=2.0 GeV, with two- and one-loop matching, respectively. We demonstrate that the simultaneous application of RGR and LRR significantly reduces the systematic errors in renormalized matrix elements and distributions for both the zero and nonzero skewness GPDs, and that it is necessary to include both RGR and LRR at higher orders in the matching and renormalization processes. Published by the American Physical Society 2024

N3LO power corrections for 0-jettiness subtractions with fiducial cuts

We compute the leading logarithmic power corrections at next-to-next-to-next-to-leading order for 0-jettiness subtractions for Drell-Yan and Higgs production in gluon fusion differential in both the invariant mass and rapidity of the color singlet. We review how to disentangle these power corrections from those arising from the presence of fiducial and isolation cuts by using Projection-to-Born improved slicing. Our results include all the channels contributing at leading logarithmic order for these processes, including the off-diagonal channels that receive contributions from soft quark emission. We study the numerical impact of the power corrections for Drell-Yan and Higgs production and find it to become negligible compared to the size of the N3LO corrections only below τcut ~ 10−5. We estimate that in a fully differential calculation at N3LO combining the Projection-to-Born improved slicing method and our results for the leading logarithmic power corrections may allow for keeping the slicing uncertainties under control already with τcut ≲ 10−3, marking a significant improvement in efficiency for these methods. These results constitute a crucial ingredient for fully differential N3LO calculations based on the N-jettiness subtraction scheme.

Phase estimation via multi-photon subtraction inside the SU(1,1) interferometer

To improve the phase sensitivity, multi-photon subtraction schemes (multi-PSS) within the SU(1,1) interferometer are proposed. The input states are the coherent state and the vacuum state, and the detection method is homodyne detection. The effects of multi-photon subtraction on phase sensitivity, quantum Fisher information (QFI), and quantum Cramér-Rao bound (QCRB) are analyzed under both ideal and photon losses situations. It is shown that the internal subtraction operation can improve the phase sensitivity, which becomes better performance by increasing subtraction number. It can also efficiently improve the robustness of the SU(1,1) interferometer against internal photon losses. By comparing separatively arbitrary photon subtraction on the two-mode inside SU(1,1) interferometer, the performance differences under different conditions are analyzed, including the asymmetric properties of non-Gaussian operations on the phase precision and the QFI. Our proposed scheme represents a valuable method for achieving quantum precision measurements.

Transverse momentum-dependent heavy-quark fragmentation at next-to-leading order

The transverse momentum-dependent fragmentation functions (TMD FFs) of heavy (bottom and charm) quarks, which we recently introduced, are universal building blocks that enter predictions for a large number of observables involving final-state heavy quarks or hadrons. They enable the extension of fixed-order subtraction schemes to quasi-collinear limits, and are of particular interest in their own right as probes of the nonperturbative dynamics of hadronization. In this paper we calculate all TMD FFs involving heavy quarks and the associated TMD matrix element in heavy-quark effective theory (HQET) to next-to-leading order in the strong interaction. Our results confirm the renormalization properties, large-mass, and small-mass consistency relations predicted in our earlier work. We also derive and confirm a prediction for the large-z behavior of the heavy-quark TMD FF by extending, for the first time, the formalism of joint resummation to capture quark mass effects in heavy-quark fragmentation. Our final results in position space agree with those of a recent calculation by another group that used a highly orthogonal organization of singularities in the intermediate momentum-space steps, providing a strong independent cross check. As an immediate application, we present the complete quark mass dependence of the energy-energy correlator (EEC) in the back-to-back limit at Oαs\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\mathcal{O}\\left({\\alpha}_s\\right) $$\\end{document}.

Perturbative versus non-perturbative renormalization

Approximated functional renormalization group (FRG) equations lead to regulator-dependent β-functions, in analogy to the scheme-dependence of the perturbative renormalization group (pRG) approach. A scheme transformation redefines the couplings to relate the β-functions of the FRG method with an arbitrary regulator function to the pRG ones obtained in a given scheme. Here, we consider a periodic sine-Gordon scalar field theory in d = 2 dimensions and show that the relation of the FRG and pRG approaches is intricate. Although both the FRG and the pRG methods are known to be sufficient to obtain the critical frequency βc2=8π of the model independently of the choice of the regulator and the renormalization scheme, we show that one has to go beyond the standard pRG method (e.g. using an auxiliary mass term) or the Coulomb-gas representation in order to obtain the β-function of the wave function renormalization. This aspect makes the scheme transformation non-trivial. Comparing flow equations of the two-dimensional sine-Gordon theory without any scheme-transformation, i.e. redefinition of couplings, we find that the auxiliary mass pRG β-functions of the minimal subtraction scheme can be recovered within the FRG approach with the choice of the power-law regulator with b = 2, which therefore constitutes a preferred choice for the comparison of FRG and pRG flows.

Transverse momentum moments

We establish robust relations between Transverse Momentum Dependent distributions (TMDs) and collinear distributions. We define weighted integrals of TMDs that we call Transverse Momentum Moments (TMMs) and prove that TMMs are equal to collinear distributions evaluated in some minimal subtraction scheme. The conversion to the modified minimal subtraction (MS¯) scheme can be done by a calculable factor, which we derive up to three loops for some cases. We discuss in detail the zeroth, the first, and the second TMMs and provide phenomenological results for them based on the current extractions of TMDs. The results of this paper open new avenues for theoretical and phenomenological investigation of the three-dimensional and collinear hadron structures. Published by the American Physical Society 2024

Deterministic single photon subtraction with a cascade of waveguide-coupled atoms.

We present a specialized photon subtraction scheme that allows for the deterministic extraction of single photons from multiphoton states while preserving the input single-photon states unaltered. The proposed device integrates two Λ-type emitters with transitions selectively coupled to a single chiral waveguide through single photon Raman interaction (SPRINT). We develop a comprehensive theoretical model for the system using the input-output formalism within the SLH framework and conduct numerical simulations to analyze its interaction with traveling few-photon pulses of coherent light. We use these simulations to predict the scheme's operation and highlight how this two-emitter extension improves the original SPRINT-based deterministic single-photon subtraction when it comes to implementing undetectable photon number splitting attack on a quantum key distribution channel.

A new subtraction scheme at NLO exploiting the privilege of kT-factorization

We present a subtraction method for the calculation of real-radiation integrals at NLO in hybrid kT-factorization. The main difference with existing methods for collinear factorization is that we subtract the momentum recoil, occurring due to the mapping from an (n + 1)-particle phase space to an n-particle phase space, from the initial-state momenta, instead of distributing it over the final-state momenta.

A subtraction scheme for processes involving fragmentation functions at NLO

We present a novel subtraction method to remove the soft and collinear divergences at next-to-leading order for processes involving an arbitrary number of fragmentation functions, where this method acts directly in the hadronic centre-of-mass frame. We provide the analytical formulae of the subtraction terms in the general case where all the final state partons fragment to hadrons and for the two special cases when one of the partons of the final state does not fragment, i.e. it is a photon or involved in a jet.

Error suppression in multicomponent cat codes with photon subtraction and teleamplification

It is known that multiphoton states can be protected from decoherence due to a passive loss channel by applying noiseless attenuation before and noiseless amplification after the channel. In this work, we propose the combined use of multiphoton subtraction on four-component cat codes and teleamplification to effectively suppress errors under detection and environmental losses. The back-action from multiphoton subtraction modifies the encoded qubit encoded on cat states by suppressing the higher photon numbers, while simultaneously ensuring that the original qubit can be recovered effectively through teleamplification followed by error correction, thus preserving its quantum information. With realistic photon subtraction and teleamplification-based scheme followed by optimal error-correcting maps, one can achieve a worst-case fidelity (over all encoded pure states) of over 93.5% (82% with only noisy teleamplification) at a minimum success probability of about 3.42%, under a 10% environmental-loss rate, 95% detector efficiency and sufficiently large cat states with the coherent-state amplitudes of 2. This sets a promising standard for combating large passive losses in quantum-information tasks in the noisy intermediate-scale quantum (NISQ) era, such as direct quantum communication or the storage of encoded qubits on the photonic platform.

Gradient properties of perturbative multiscalar RG flows to six loops

The gradient property of the renormalisation group (RG) flow of multiscalar theories is examined perturbatively in d=4 and d=4−ε dimensions. Such theories undergo RG flows in the space of quartic couplings λI. Starting at five loops, the relevant vector field that determines the physical RG flow is not the beta function traditionally computed in a minimal subtraction scheme in dimensional regularisation, but a suitable modification of it, the B function. It is found that up to five loops the B vector field is gradient, i.e. BI=GIJ∂A/∂λJ with A a scalar and GIJ a rank-two symmetric tensor of the couplings. Up to five loops the beta function is also gradient, but it fails to be so at six loops. The conditions under which the B function (and hence the RG flow) is gradient at six loops are specified, but their verification rests on a separate six-loop computation that remains to be performed.

Pion valence quark distribution at physical pion mass of N f = 2 + 1 + 1 lattice QCD

We present a state-of-the-art calculation of the unpolarized pion valence-quark distribution in the framework of large-momentum effective theory (LaMET) with improved handling of systematic errors as well as two-loop perturbative matching. We use lattice ensembles generated by the MILC collaboration at lattice spacing a ≈ 0.09 fm, lattice volume 643 × 96, N f = 2 + 1 + 1 flavors of highly-improved staggered quarks and a physical pion mass. The LaMET matrix elements are calculated with pions boosted to momentum P z ≈ 1.72 GeV with high-statistics of O(106) measurements. We study the pion PDF in both hybrid-ratio and hybrid-regularization-independent momentum subtraction (hybrid-RI/MOM) schemes and also compare the systematic errors with and without the addition of leading-renormalon resummation (LRR) and renormalization-group resummation (RGR) in both the renormalization and lightcone matching. The final lightcone PDF results are presented in the modified minimal-subtraction scheme at renormalization scale μ = 2.0 GeV. We show that the x-dependent PDFs are compatible between the hybrid-ratio and hybrid-RI/MOM renormalization with the same improvements. We also show that systematics are greatly reduced by the simultaneous inclusion of RGR and LRR and that these methods are necessary if improved precision is to be reached with higher-order terms in renormalization and matching.