Loop Contributions Research Articles

Wilson line-based action for gluodynamics at the loop level

We develop quantum corrections to the Wilson line-based action which we recently derived through a transformation that eliminates triple gluon vertices from the Yang-Mills action on the light-cone. The action efficiently computes high multiplicity tree-level split-helicity amplitudes with the number of diagrams following the Delannoy number series. However, the absence of the triple gluon vertices results in missing loop contributions. To remedy this, we develop two equivalent approaches using the one-loop effective action method to systematically incorporate loop contributions to our action. In one approach there are solely Yang-Mills vertices in the loop whereas the other uses the interaction vertices of our action along with the kernels of the solution of our transformation in the loop. In addition to demonstrating the equivalence of both approaches, we validated the quantum completeness of the former by computing all 4-point one-loop amplitudes which could not be previously computed. Both of our approaches are easily extendable to develop quantum corrections to other reformulations of the Yang-Mills theory obtained via non-linear classical field transformations eliminating interaction vertices.

Heavy-to-light form factors to three loops

We compute three-loop corrections of O(αs3) to form factors with one massive and one massless quark coupling to an external vector, axialvector, scalar, pseudoscalar, or tensor current. We obtain analytic results for the color-planar contributions, for the contributions of light-quark loops, and the contributions with two heavy-quark loops. For the computation of the remaining master integrals we use the “expand and match” approach which leads to semianalytic results for the form factors. We implement our results in a and a ortran code which allows for fast and precise numerical evaluations in the physically relevant phase space. The form factors are used to compute the hard matching coefficients in Soft-Collinear Effective Theory for all currents. The tensor coefficients at lightlike momentum transfer are used to extract the hard function in B¯→Xsγ to three loops. Published by the American Physical Society 2024

Revealing the mechanism of subsynchronous torsional interaction caused by LCC-HVDC from the perspective of vector synchronization

Line-commutated converter-based high voltage direct current transmission (LCC-HVDC) has been widely applied worldwide due to its great advantages in realizing long-distance and large-capacity power transmission. However, it may also lead to instability problems, including subsynchronous torsional interaction (SSTI). This destructive phenomenon greatly threatens the safe and stable operation of power systems and has been widely concerned since the 1970 s. Existing literature has found that SSTI is caused by DC current control of rectifier station. However, the physical mechanism of this phenomenon has not been clarified clearly, which hampers further understanding of how negative damping is generated and whether it is evitable. To fill this gap, the physical process of SSTI caused by LCC-HVDC is clarified through the perspective of vector synchronization. Based on this, the negative damping mechanism is revealed. The influence of control on damping is also studied with the contribution of different control loops quantified. All results are verified through time-domain simulations and damping torque analysis.

Nonfactorizable charming-loop contribution to FCNC Bs→γl+l− decay

We present the first theoretical calculation of nonfactorizable charm-quark loop contributions to the Bs→γl+l− amplitude. We calculate the relevant form factors, HA,VNF(k′2,k2), and provide convenient parametrizations of our results in the form of fit functions of two variables, k′2 and k2, applicable in the region below hadron resonances, k′2<MJ/ψ2 and k2<Mϕ2. We report that factorizable and nonfactorizable charm contributions to the Bs→γl+l− amplitude have opposite signs. To compare the charm and the top contributions, it is convenient to express nonfactorizable charming loop contribution as a nonuniversal (i.e., dependent on the reaction) q2-dependent correction ΔNFC7(q2) to the Wilson coefficient C7. For the Bs→γl+l− amplitude, the correction is found to be positive, ΔNFC7(q2)/C7>0. Published by the American Physical Society 2024

Production of Xb via radiative transition of ϒ(10753)

We studied the radiative transitions between the ϒ(10753), the S−D mixed state of the ϒ(4S) and ϒ1(3D13), and the Xb, the heavy quark flavor symmetry counterpart of the X(3782) in the bottomonium sector. The radiative transition was assumed to occur through the intermediate bottom mesons, including P-wave B1(′) mesons as well as the S-wave B(*) ones. The consideration of the B1(′) mesons leads to the couplings to be in S-wave, and hence enhances the contributions of the intermediate meson loops. The radiative decay width for the ϒ(10753)→γXb is predicted to be order of 10 keV, corresponding to a branching fraction of 10−4. Based on the theoretical results, we strongly suggest to search for the Xb in the e+e−→γXb with Xb→ππχb1 near s=10.754 GeV, and it is hoped that the calculations here could be tested by the future Belle II experiments. Published by the American Physical Society 2024

On β-function of N = 2 supersymmetric integrable sigma-models

We study the regularization scheme dependence of Kähler (N = 2) supersymmetric sigma models. At the one-loop order the metric β function is the same as in the non-supersymmetric case and it coincides with the Ricci tensor. The first correction in the MS scheme is known to appear in the fourth loop [1, 2]. We show that for certain integrable Kähler backgrounds, such as the complete T-dual of η-deformed CPn\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\mathbbm{CP}(n) $$\\end{document} sigma models, there is a scheme in which the fourth loop contribution vanishes.

Total cross section of the process e++e−→Σ0+Σ¯0 in the vicinity of charmonium ψ(3770) including the D -meson loop and three-gluon contributions

For the study of the structure of baryons it is necessary to investigate the production of a baryon pair in e+e− annihilation. The baryon-antibaryon pair production at the electron-positron linear collider makes it possible to investigate in detail the basic structure of the Standard Model. The creation of baryon-antibaryon pairs in electron-positron annihilation provides an increasingly powerful tool at higher c.m. energies. We present phenomenological results for Σ0Σ¯0 production in e+e− interaction at the BESIII and Colliders. In the present work, we investigate a hyperon pair produced in the reaction e+e−→Σ0Σ¯0. We calculate the total cross section of the process e+e−→Σ0Σ¯0 taking into account the contributions of the D-meson loop and three gluon loops as well as the interference of all diagrams to the Born approximation. For these contributions large relative phases are generated with respect to the pure electromagnetic mechanism. For the large momentum transferred region we obtain as a byproduct a fit of the electromagnetic form factor of the Σ hyperon. Published by the American Physical Society 2024

Analysis of final state lepton polarization-dependent observables in H → ℓ+ℓ−γ in the SM at loop level

Recently, the CMS and ATLAS collaborations have announced the results for H → Z[→ ℓ+ℓ−]γ with ℓ = e or μ [1, 2], where H → Zγ is a sub-process of H → ℓ+ℓ−γ. This semi-leptonic Higgs decay gets both resonant and non-resonant contributions from the loop-induced H → Z[→ ℓ+ℓ−]γ. To probe further features coming from these contributions to H → ℓ+ℓ−γ, we argue that the polarization of the final state leptons is also an important parameter. We show that the interference of resonant and non-resonant contributions, which is negligible in the case of unpolarized leptons, plays a significant role when considering the polarization of the final state lepton. For this purpose, we have calculated the polarized decay rates and the longitudinal (PL), normal (PN), and transverse (PT) polarization asymmetries. We find that these asymmetries purely come from the loop contributions and are helpful to further investigate the resonant and non-resonant nature of H → Z[→ ℓ+ℓ−]γ decay. We observe that for ℓ = e, μ, the longitudinal decay rate is highly suppressed around mℓℓ ≈ 60 GeV when the final lepton spin is −12\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ -\\frac{1}{2} $$\\end{document}, dramatically increasing the corresponding lepton polarization asymmetries. Furthermore, we analyze another observable, the ratio of decay rates Ri±ll′\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {R}_{i\\pm}^{{\\mathcal{ll}}^{\\prime }} $$\\end{document}, where ℓ and ℓ′ refer to different final state lepton generations. Precise measurements of these observables at the HL-LHC and the planned e+e− collider can provide fertile ground to test not only the SM but also to examine the signatures of possible NP beyond the SM.

Loop contributions to the scalar power spectrum due to quartic order action in ultra slow roll inflation

The investigation of the theory of inflation beyond the linearorder in perturbations is important both for theoretical consistency andpotential observables.In the contemporary literature, the calculation of modifications to theinflationary scalar power spectrum due to the loops from the higher orderinteraction terms in the Hamiltonian have led to an interesting discussionregarding the validity of perturbation theory and the robustness of itspredictions.Recently, there have been many efforts to examine the contributions to thescalar power spectrum due to the loops arising from the cubic order termsin the action describing the perturbations, specifically in inflationaryscenarios that permit an epoch of ultra slow roll (USR).A brief phase of USR during inflation is known to lead to interesting featuresin the scalar power spectrum which in turn has significant observationalconsequences, such as the copious production of primordial black holes.In this work, we consider the loop contributions to the scalar power spectrumin a scenario of USR inflation arising due to the quartic order termsin the action describing the scalar perturbations.We compute the loop contributions to the scalar power spectrum due to thedominant term in the action at the quartic order in a scenario wherein ashort phase of USR is sandwiched between two stages of slow roll (SR) inflation.We analyze the behaviour of the loop contributions in terms of the parametersthat characterize the non-trivial inflationary dynamics, viz. the onset andduration of USR, and the smoothness of transitions between the USR and SR phases.We examine three different cases of the scenario — the late, intermediate andearly epochs of USR during inflation, each of which affects the scalar powerspectrum over different ranges of wave numbers.In the inflationary scenario involving a late phase of USR, for reasonable choicesof the parameters, we show that the loop corrections are negligible for the entirerange of wave numbers.In the intermediate case, the contributions from the loops prove to be scaleinvariant over large scales and, we find that these contributions can amountto 30% of the leading order (i.e. the Gaussian) power spectrum.In the case wherein USR sets in early, we find that the loop contributions couldbe negative and can dominate the power spectrum at the leading order, whichindicates a breakdown of the validity of the perturbative expansion.We discuss the origin of the negative sign and the divergences that arise in theloop contributions to the power spectrum.We conclude with a brief summary and outlook.

Entanglement entropy in scalar quantum electrodynamics

We find the entanglement entropy of a subregion of the vacuum state in scalar quantum electrodynamics, working perturbatively to the two-loop level. Doing so leads us to derive the Maxwell-Proca propagator in conical Euclidean space. The area law of entanglement entropy is recovered in both the massive and massless limits of the theory, as is expected. These results yield the renormalization group flow of entanglement entropy, and we find that loop contributions suppress entanglement entropy. We highlight these results in the light of the renormalization group flow of couplings and correlators, which are increased in scalar quantum electrodynamics, so that the potential tension between the increase in correlations between two points of spacetime and the decrease in entanglement entropy between two regions of spacetime with energy is discussed. We indeed show that the vacuum of a subregion of spacetime purifies with energy in scalar quantum electrodynamics, which is related to the concept of screening. Published by the American Physical Society 2024

Gravitational p → ∆+ transition form factors in chiral perturbation theory

The gravitational form factors of the transition from the proton to the ∆+ resonance are calculated to leading one-loop order using a manifestly Lorentz-invariant formulation of chiral perturbation theory. We take into account the leading electromagnetic and strong isospin-violating effects. The loop contributions to the transition form factors are found to be free of power-counting violating pieces, which is consistent with the absence of tree-level diagrams at the considered order. In this sense, our results can be regarded as predictions of chiral perturbation theory.

Bubble nucleation in the two-flavor quark-meson model* *Supported in part by the National Natural Science Foundation of China (NSFC) (11675048)

We investigate the dynamics of a first-order quark-hadron transition via homogeneous thermal nucleation in the two-flavor quark-meson model. The contribution of the fermionic vacuum loop in the effective thermodynamics potential and phase diagram, together with the location of the critical endpoint (CEP), is obtained in the temperature and chemical potential plane. For weak and strong first-order phase transitions, by taking the temperature as a variable, the critical bubble profiles, evolutions of the surface tension, and saddle-point action in the presence of a nucleation bubble are numerically calculated in detail when fixing the chemical potentials at and . Our results show that the system could be trapped in the metastable state for a long time as long as the temperature is between the metastable region characterized by the up and low spinodal lines. Moreover, the surface tension at criticality will rise to approximately when the chemical potential is very high. Such a small surface tension value would favor a mixed phase in the cores of compact stars and may have an important implication in astrophysics.

Sea-quark loop contributions to the d¯−u¯ asymmetry in the proton

QCD interactions for equal-mass fermion flavors are flavor blind. This fact is often used to state that disconnected sea-quark loop contributions are equal for u and d quarks in the mass symmetric case and therefore these disconnected sea-quark loop contributions cannot contribute to the well-known d¯−u¯ asymmetry in the proton. Instead, it is argued that one must look to the connected sector of lattice QCD correlation functions to find this difference. In this presentation, we note that these statements are true provided unphysical contributions in the sea-quark loop sector are included, contributions from baryons that do not appear in the physical spectrum. To respect the Pauli principle, these unphysical contributions from the disconnected sea-quark loop sector must cancel equally unphysical contributions in the connected sector. The remaining disconnected sea-quark loop contributions no longer have a balance between d¯ and u¯. Upon considering only physically observed baryons in the loop contributions, we illustrate an important contribution from the sea-quark loop sector to d¯−u¯ that enhances the leading connected contribution by 12%. Published by the American Physical Society 2024

Electroweak loop contributions to the direct detection of wino dark matter

Electroweak loop corrections to the matrix elements for the spin-independent scattering of cold dark matter particles on nuclei are generally small, typically below the uncertainty in the local density of cold dark matter. However, as shown in this paper, there are instances in which the electroweak loop corrections are relatively large, and change significantly the spin-independent dark matter scattering rate. An important example occurs when the dark matter particle is a wino, e.g., in anomaly-mediated supersymmetry breaking (AMSB) and pure gravity mediation (PGM) models. We find that the one-loop electroweak corrections to the spin-independent wino LSP scattering cross section generally interfere constructively with the tree-level contribution for AMSB models with negative Higgsino mixing, mu < 0, and in PGM-like models for both signs of mu , lifting the cross section out of the neutrino fog and into a range that is potentially detectable in the next generation of direct searches for cold dark matter scattering.

Galaxy bias renormalization group

The effective field theory of large-scale structure allows for a consistent perturbative bias expansion of the rest-frame galaxy density field. In this work, we present a systematic approach to renormalize galaxy bias parameters using a finite cutoff scale Λ. We derive the differential equations of the Wilson-Polchinski renormalization group that describe the evolution of the finite-scale bias parameters with Λ, analogous to the β-function running in QFT. We further provide the connection between the finite-cutoff scheme and the renormalization procedure for n-point functions that has been used as standard in the literature so far; some inconsistencies in the treatment of renormalized bias in current EFT analyses are pointed out as well. The fixed-cutoff scheme allows us to predict, in a principled way, the finite part of loop contributions which is due to perturbative modes and which, in the standard renormalization approach, is absorbed into counterterms. We expect that this will allow for the robust extraction of (a yet-to-be-determined amount of) additional cosmological information from galaxy clustering, both when using field-level techniques and n-point functions.

Enhancing the fracture toughness of laminated composites through loop warp yarns

The delamination tendency is a key factor affecting the practical use of laminated composites. How to improve the interlaminar strength and interlaminar fracture toughness of laminated composite is a focus of research on composite materials. A three-dimensional (3D) weaving technique is employed to weave loop warp yarns (loops) with 3D fiber bundles instead of warp yarns on the basis of plain fabrics. The contribution of loops to the interlayer performance is revealed by double cantilever beam (DCB) tests, end-notch flexure (ENF) tests, flexural tests, and double notch shear (DNS) tests. Test results show that the mode I and mode II interlaminar fracture toughness values of the single-sided-loop two-dimensional (2D) woven laminated composite (SWLC) are 77% and 58.2% higher than the interlaminar fracture toughness values of the general 2D woven laminated composite (GWLC). As companied with the ones of GWLC, flexural strength and modulus of SWLC increase by 73% and 69.1%, and the interlaminar shear strength of SWLC increases by 45.7%. The loop yarns act as a link between the interlaminar matrix and the reinforcing fiber fabric and thus improve the poor interlaminar performance of GWLC. The reported information may provide a reference for the application of the SWLC in practice.

Fermion geometry and the renormalization of the Standard Model Effective Field Theory

The geometry of field space governs on-shell scattering amplitudes. We formulate a geometric description of effective field theories which extends previous results for scalars and gauge fields to fermions. The field-space geometry reorganizes and simplifies the computation of quantum loop corrections. Using this geometric framework, we calculate the fermion loop contributions to the renormalization group equations for bosonic operators in the Standard Model Effective Field Theory up to mass dimension eight.

Leading loops in cosmological correlators

Cosmological correlators from inflation are often generated at tree level and hence loop contributions are bounded to be small corrections by perturbativity. Here we discuss a scenario where this is not the case. Recently, it has been shown that for any number of scalar fields of any mass, the parity-odd trispectrum of a massless scalar must vanish in the limit of exact scale invariance due to unitarity and the choice of initial state. By carefully handling UV-divergences, we show that the one-loop contribution is non-vanishing and hence leading. Surprisingly, the one-loop parity-odd trispectrum is simply a rational function of kinematics, which we compute explicitly in a series of models, including single-clock inflation. Although the loop contribution is the leading term in the parity-odd sector, its signal-to-noise ratio is typically bounded from above by that of a corresponding tree-level parity-even trispectrum, unless instrumental noise and systematics for the two observables differ. Furthermore, we identify a series of loop contributions to the wavefunction that cancel exactly when computing correlators, suggesting a more general phenomenon.

Lighting up the LHC with Dark Matter

We show that simultaneously explaining dark matter and the observed value of the muon’s magnetic dipole moment may lead to yet unexplored photon signals at the LHC. We consider the Minimal Supersymmetric Standard Model with electroweakino masses in the few-to-several hundred GeV range, and opposite sign of the Bino mass parameter with respect to both the Higgsino and Wino mass parameters. In such region of parameter space, the spin-independent elastic scattering cross section of a Bino-like dark matter candidate in direct detection experiment is suppressed by cancellations between different amplitudes, and the observed dark matter relic density can be realized via Bino-Wino co-annihilation. Moreover, the observed value of the muon’s magnetic dipole moment can be explained by Bino and Wino loop contributions. Interestingly, “radiative” decays of Wino-like neutralinos into the lightest neutralino and a photon are enhanced, whereas decays into leptons are suppressed. While these decay patterns weaken the reach of multi-lepton searches at the LHC, the radiative decay opens a new window for probing dark matter at the LHC through the exploration of parameter space regions beyond those currently accessible. To complement the current electroweakino searches, we propose searching for a single (soft) photon plus missing transverse energy, accompanied by a hard initial state radiation jet.

A missing trophic link: Contribution of the microbial loop to the estimation of the trophic position of pelagic consumers

AbstractTrophic position estimation has been a central issue in food web studies. Estimates using compound‐specific isotopic analyses of amino acids were generally based on the trophic enrichment of glutamic acid. However, this trophic position estimation mainly accounts for the trophic steps involving metazoa, as the isotopic fractionation of this amino acid is minimal at trophic steps within the microbial food web. Alternatively, trophic position estimates based on alanine seem to also reflect microbial trophic steps. The difference between these estimations can provide an index of the microbial food web contribution to the trophic position of a particular consumer. Here, we examined the differences between both trophic position estimates through a meta‐analysis of the published data over a large range of marine consumers. The results suggest that the microbial contribution to trophic position decreases as trophic position increases in the marine pelagic food web, showing the lowest values in top consumers. Ureotelic organisms showed the highest microbial contributions. The current data point to an upper limit for the estimation of this index at δ15N values of glutamic acid or alanine of ~ 18.5‰, or trophic positions of 3.9 or 4.7 for fish and ammoniotelic organisms, respectively. Under the stable isotope lens, bacteria and protists may play a key role in the estimation of trophic positions of consumers. However, uncertainties that related both to the microbial loop (e.g., metabolic bacterial pathways) and to metazoan consumers (e.g., influence of the gut microbiome) still obscure the establishment of clear quantitative links between microbial and metazoan food webs.