One-loop Research Articles

Polarized gluon pseudodistributions at short distances

We formulate the basic points of the pseudo-PDF approach to the lattice calculation of polarized gluon PDFs. We present the results of our calculations of the one-loop corrections for the bilocal Gμα(z) overset{sim }{G} λβ (0) correlator of gluonic fields. Expressions are given for a general situation when all four indices are arbitrary, and also for specific combinations of indices corresponding to three matrix elements that contain the twist-2 invariant amplitude related to the polarized PDF. We study the evolution properties of these matrix elements, and derive matching relations between Euclidean and light-cone Ioffe-time distributions. These relations are necessary for extraction of the polarized gluon distributions from the lattice data.

Achieving Effective Renormalization Scale and Scheme Independence via the Principle of Observable Effective Matching

In this work, we explicate a new approach for eliminating renormalization scale and scheme (RSS) dependence in observables. We develop this approach by matching RSS-dependent observables (such as cross-sections and decay rates) to a theory which is independent of both these forms of dependencies. We term the fundamental basis behind this approach as the principle of observable effective matching (POEM), which entails matching of a scale- and scheme-dependent observable with the fully physical scale (PS) and dynamical scale-dependent theory at loop orders at which RSS independence is guaranteed. This is aimed toward achieving so-called “effective” RSS-independent expressions as the resulting dynamical dependence is derived from a particular order in RSS-dependent perturbation theory. With this matching at a PS at which the coupling (and masses) is experimentally determined at this scale, we obtain an “effective theoretical observable (ETO)”, a finite-order RSS-independent version of the RSS-dependent observable. We illustrate our approach with a study of the cross-section ratio Re+e− for e+e− → hadrons, which is demonstrated to achieve scale and scheme independence utilizing the three- and four-loop order MS̄ scheme expression in QCD perturbation theory via matching at both one-loop and two-loop orders for obtaining the ETO. With two-loop matching, we obtain an ETO prediction of 311Re+e−eff=1.052431−0.0006+0.0006 at Q = 31.6GeV, which is in excellent agreement with the experimental value of 311Re+e−exp=1.0527−0.005+0.005. Given its new conceptual basis, ease of use, and performance, we contend that POEM be explored in its application for obtaining ETOs for predicting RSS-independent observables across domains of high-energy theory and phenomenology as well as other areas of fundamental and applied physics, such as cosmology and statistical and condensed matter physics.

Universal properties of active membranes.

We put forward a general field theory for nearly flat fluid membranes with embedded activators and analyze their critical properties using renormalization group techniques. Depending on the membrane-activator coupling, we find a crossover between acoustic and diffusive scaling regimes, with mean-field dynamical critical exponents z=1 and 2, respectively. We argue that the acoustic scaling, which is exact in all spatial dimensions, leads to an early-time behavior, which is representative of the spatiotemporal patterns observed at the leading edge of motile cells, such as oscillations superposed on the growth of the membrane width. In the case of mean-field diffusive scaling, one-loop corrections to the mean-field exponents reveal universal behavior distinct from the Kardar-Parisi-Zhang scaling of passive interfaces and signs of strong-coupling behavior.

Three-loop order approach to flat polymerized membranes.

We derive the three-loop order renormalization group equationsthat describe the flat phase of polymerized membranes within the modified minimal subtraction scheme, following the pioneering one-loop order computation of Aronovitz and Lubensky [Phys. Rev. Lett. 60, 2634 (1988)10.1103/PhysRevLett.60.2634] and the recent two-loop order one of Coquand, Mouhanna, and Teber [Phys. Rev. E 101, 062104 (2020)2470-004510.1103/PhysRevE.101.062104]. We analyze the fixed points of these equationsand compute the associated field anomalous dimension η at three-loop order. Our results display a marked proximity with those obtained using nonperturbative techniques and reexpanded in powers of ε=4-D. Moreover, the three-loop order value that we get for η at the stable fixed point, η=0.8872, in D=2, is compatible with known theoretical results and within the range of accepted numerical values.

One-loop correction to the AdS/BCFT partition function in three-dimensional pure gravity

We calculate the tree-level partition function of Euclidean BTZ black hole with the end of the world branes (ETW branes) for arbitrary tension and the one-loop partition function of Euclidean thermal $AdS_{3}$ in the presence of a tensionless ETW brane with the Neumann boundary condition. At the tree level, our results match with the previous ones in non-rotating cases, but at the one-loop level, our results contain unexpected terms, which contain the fluctuations of the ghost fields. However particularly in the case where the chemical potential is zero, we get a similar form as the original result in AdS/CFT case, but the exponent is slightly changed. In this case the ghost contribution looks going away and the partition function becomes physical in a sense that the coefficients of the expansion in powers of $q$ are positive, which means that the number of states at the level is always positive.

Chiral theory of ρ -meson gravitational form factors

The low-energy chiral effective field theory of vector mesons and Goldstone bosons in external gravitational field is considered. The energy-momentum tensor is obtained and the gravitational form factors of the $\rho$-meson are calculated up to next-to-leading order in the chiral expansion. This amounts to considering tree-level and one-loop order diagrams. The chiral expansion of the form factors at zero momentum transfer as well as of the slope parameters is worked out. Also, the long-range behaviour of the energy and internal force distributions is obtained and analysed.

One-loop Form Factors for \(H\rightarrow \gamma^*\gamma^*\) in \(R_{\xi}\) Gauge

In this paper, we present general one-loop form factors for \(H\rightarrow \gamma^* \gamma^*\) in \(R_{\xi}\) gauge, considering all cases of two on-shell, one on-shell and two off-shell for final photons. The calculations are performed in standard model and in arbitrary beyond the standard models which charged scalar particles may be exchanged in one-loop diagrams. Analytic results for the form factors are shown in general forms which are expressed in terms of the Passarino-Veltman functions. We also confirm the results in previous computations which are available for the case of two on-shell photons. The \(\xi\)-independent of the result is also discussed. We find that numerical results are good stability with varying \(\xi=0,1\) and \(\xi\rightarrow \infty\).

Computing one-loop radiative corrections in τ → π(K)ν[γ] and testing new physics

Without a doubt the ratios Rτ/p = Γ(τ → Pντ[γ])/Γ(P → μνμ[γ]) (P = π, K) give a convenient scenario to test the lepton universality, the CKM unitarity and to search for non-standard interactions in τ decays. Moreover, the previous theoretical estimation of these observables is more than twenty-five years old and some assumptions of that estimation are unrealistic. Therefore, an update of Rτ/P was timely. The one-loop radiative corrections have been computed by considering an expansion of Chiral Perturbation Theory including the lightest spin-one resonances and respecting the short-distance behavior dictated by QCD. We have reported δRτ/π = (0.18±0.57)% and δRτ/K = (0.97±0.58)%, where the uncertainties have been induced fundamentally by the estimation of the counterterms. We have tested the lepton universality, the CKM unitarity and have searched for new physics in τ decays. As a by-product, we have also determined the theoretical radiative corrections to the τ → Pντ[γ] decay rates, δτπ = —(0.24 ± 0.56)% and δτK = —(0.15 ± 0.57)%.

Charged lepton EDM with extra Yukawa couplings

In a two Higgs doublet model with extra Yukawa couplings, we assess the new physics contributions to charged lepton electric dipole moment. We focus especially on muon (and tau) EDM where in the coming decade several experiments — Muon g-2, J-PARC and PSI (and Belle II) — will push sensitivities down by several orders of magnitude. With the working assumption that extra Yukawa couplings are analogous to SM ones in strength and taking exotic scalar masses in sub-TeV range, we find that μ and τ EDM can be enhanced to values larger than new physics scenarios that scale with lepton mass. The main effect comes from the flavor-conserving extra top coupling ρtt via well-known two-loop diagrams. Deviating from our working assumption, if the muon g − 2 anomaly arises from the one-loop diagram, driven by singly enhanced lepton flavor violating ρτμ coupling, it can also induce rather large muon EDM, accessible at upcoming experiments.

Graviton corrections to the Newtonian potential using invariant observables

We consider the effective theory of perturbative quantum gravity coupled to a point particle, quantizing fluctuations of both the gravitational field and the particle’s position around flat space. Using a recent relational approach to construct gauge-invariant observables, we compute one-loop graviton corrections to the invariant metric perturbation, whose time-time component gives the Newtonian gravitational potential. The resulting quantum correction consists of two parts: the first stems from graviton loops and agrees with the correction derived by other methods, while the second one is sourced by the quantum fluctuations of the particle’s position and energy-momentum, and may be viewed as an analog of a “Zitterbewegung”. As a check on the computation, we also recover classical corrections which agree with the perturbative expansion of the Schwarzschild metric.

Perturbatively exact w1+\u221e asymptotic symmetry of quantum self-dual gravity

The infinite tower of positive-helicity soft gravitons in any minimally coupled, tree-level, asymptotically flat four-dimensional (4D) gravity was recently shown to generate a w1+∞ asymptotic symmetry algebra. It is natural to ask whether this classical algebra acquires quantum corrections at loop level. We explore this in quantum self-dual gravity, whose amplitudes acquire known one-loop exact all-plus helicity quantum corrections. We show using collinear splitting formulae that, remarkably, the w1+∞ algebra persists in quantum self-dual gravity without corrections.

Universality of gauge coupling constant in the Einstein-QED system

In this paper, we discuss the universality of the renormalization of the gauge coupling constant in the quantum electrodynamics coupled to the Einstein's gravity in the framework of effective field theory in an arbitrary gauge. We observe that the renormalization of the three-point functions with different particles receive different contributions from the gravitational sector. Despite that, the universality of the gauge coupling constants is guaranteed by the Ward identity that makes the renormalized electric charge receive no contribution from the gravitational sector at one-loop order.

Baryon magnetic moment in large- Nc chiral perturbation theory: Complete analysis for Nc=3

Baryon magnetic moments are computed in baryon chiral perturbation theory in the large-$N_c$ limit at one-loop order, where $N_c$ is the number of color charges. Orders $\mathcal{O}(m_q^{1/2})$ and $\mathcal{O}(m_q \ln m_q)$ corrections are both evaluated including all the operator structures that participate at the physical value $N_c=3$. The complete expressions for octet and decuplet baryon magnetic moments in addition to decuplet-octet baryon transition moments are thus compared to their available counterparts obtained in heavy baryon chiral perturbation theory for degenerate intermediate baryons in the loops. Theoretical expressions fully agree at the physical values $N_c=3$ and $N_f=3$ flavors of light quarks. Some numerical evaluations are produced via a least-squares fit to explore the free parameters in the analysis. Results point out the necessity of incorporating the effects of non-degenerate intermediate baryons in the loops for a consistent determination of these free parameters.

QCD θ-vacuum in a uniform magnetic field

We study the θ-vacuum of QCD using two-flavor chiral perturbation theory (χPT) in the presence of a uniform, background magnetic field calculating the magnetic field-dependent free energy density, the topological density, the topological susceptibility and the fourth cumulant at one-loop order. We find that the topological susceptibility is enhanced by the magnetic field while the fourth topological cumulant is diminished at weak fields and enhanced at larger fields when θ=0. However, in the QCD vacuum with θ≠0, the topological susceptibility can be either monotonically enhanced or diminished relative to their θ-vacuum values. The fourth cumulant also exhibits monotonic enhancement or suppression except for regions of θ near 0 and 2π, where it is both diminished and enhanced. Finally, the topological density is enhanced for all magnetic fields with its relative shift being identical to the relative shift of the up and down quark condensates in the θ-vacuum.

Stochastic dynamics of chemotactic colonies with logistic growth

The interplay between cellular growth and cell-cell signaling is essential for the aggregation and proliferation of bacterial colonies, as well as for the self-organization of cell tissues. To investigate this interplay, we focus here on the collective properties of dividing chemotactic cell colonies by studying their long-time and large-scale dynamics through a renormalization group (RG) approach. The RG analysis reveals that a relevant but unconventional chemotactic interaction —corresponding to a polarity-induced mechanism— is generated by fluctuations at macroscopic scales, even when an underlying mechanism is absent at the microscopic level. This emerges from the interplay of the well-known Keller-Segel (KS) chemotactic nonlinearity and cell birth and death processes. At one-loop order, we find no stable fixed point of the RG flow equations. We discuss a connection between the dynamics investigated here and the celebrated Kardar-Parisi-Zhang (KPZ) equation with long-range correlated noise, which points at the existence of a strong-coupling, nonperturbative fixed point.

Study of electroweak penguin B decays at Belle II experiment

The electroweak b → sll (l = e, µ) transition is a flavor-changing neutral current process that mediates through a one-loop penguin diagram. The decay is considered to be a good probe for the New Physics as particles predicted in the beyond Standard Model theories can enter into the loop. The exclusive decay B → K (*) l + l − was first observed by the Belle experiment and it provides many observables such as the branching fraction, CP asymmetry, forward-backward asymmetry, and other angular observables. Recently, the LHCb experiment has reported some clue of a lepton flavor universality violation from the branching fraction ratio of the B → Kµ + µ − and B → Ke + e − decays. In this presentation, we report the status of the B → Kl + l − decay analysis at the Belle II experiment which started the data taking in 2019. We also, present an activity at the Belle II Chulalongkorn University group where we study the B → KJ/ψ decay which has the same topology as the B → Kl + l − .

Gravitational waves from the phase transition in the B-LSSM

Based on the gauge symmetry group SU(3)C ⨂ SU(2)L ⨂ U(1)Y ⨂ U(1)B–L, the minimal supersymmetric extension of the SM with local B-L gauge symmetry(B-LSSM) has been introduced. In this model, we study the Higgs masses with the one-loop zero temperature effective potential corrections. Besides, the finite temperature effective potentials connected with two U(1)B-L Higgs singlets are deduced specifically. Then we can obtain the gravitational wave spectrums generated from the strong first-order phase transition. In the B-LSSM, with the fine-tuned parameter regions, we can obtain the strength parameter αθ ~ 0.14 and the ratio of speed to Hubble rate β/Hn ~ 5 at nucleation temperature, and then obtain observable gravitational wave signals. The gravitational wave signals can be as strong as h2ΩGW ~ 10–9, which may be detectable in the future experiments.

Charged lepton flavor violation in light of muon g-2

The recent confirmation of the muon g-2 anomaly by the Fermilab g-2 experiment may harbinger a new era in mu and tau physics. In the context of general two Higgs doublet model, the discrepancy can be explained via one-loop exchange of sub-TeV exotic scalar and pseudoscalars, namely H and A, that have flavor changing neutral couplings rho _{tau mu } and rho _{mu tau } at sim 20 times the usual tau Yukawa coupling, lambda _tau . Taking rho _{ell ell ^prime }sim lambda _{ mathrm min(ell , ell ^prime )}, we show that the above solution to muon g-2 then predicts enhanced rates of various charged lepton flavor violating processes, which should be accessible at upcoming experiments. We cover muon related processes such as mu rightarrow e gamma , mu rightarrow eee and mu N rightarrow e N, and tau decays tau rightarrow mu gamma and tau rightarrow mu mu mu . A similar one-loop diagram with rho _{etau }= rho _{tau e} = mathcal{O}(lambda _e) induces mu rightarrow egamma , bringing the rate right into the sensitivity of the MEG II experiment. The mu egamma dipole can be probed further by mu rightarrow 3e and mu N rightarrow eN. With its promised sensitivity range and ability to use different nuclei, the mu N rightarrow eN conversion experiments can not only make discovery, but access the extra diagonal quark Yukawa couplings rho _{qq}. For the tau lepton, we find that tau rightarrow mu gamma would probe rho _{tau tau } down to lambda _tau or lower, while tau rightarrow 3mu would probe rho _{mu mu } to mathcal{O}(lambda _{mu }).

Factorization of log-corrections in AdS4/CFT3 from supergravity localization

We use the Atiyah-Singer index theorem to derive the general form of the one-loop corrections to observables in asymptotically anti-de Sitter (AdS4) supersymmetric backgrounds of abelian gauged supergravity. Using the method of supergravity localization combined with the factorization of the supergravity action on fixed points (NUTs) and fixed two-manifolds (Bolts) we show that an analogous factorization takes place for the one-loop determinants of supergravity fields. This allows us to propose a general fixed-point formula for the logarithmic corrections to a large class of supersymmetric partition functions in the large N expansion of a given 3d dual theory. The corrections are uniquely fixed by some simple topological data pertaining to a particular background in the form of its regularized Euler characteristic χ, together with a single dynamical coefficient that counts the underlying degrees of freedom of the theory.

One-loop structure of parton distribution for the gluon condensate and \u201czero modes\u201d

We present results for one-loop corrections to the recently introduced “gluon condensate” PDF F(x). In particular, we give expression for the gg-part of its evolution kernel. To enforce strict compliance with the gauge invariance requirements, we have used on-shell states for external gluons, and have obtained identical results both in Feynman and light-cone gauges. No “zero mode” δ(x) terms were found for the twist-4 gluon PDF F(x). However a q2δ(x) term was found for the ξ = 0 GPD F(x, q2) at nonzero momentum transfer q. Overall, our results do not agree with the original attempt of one-loop calculations of F(x) for gluon states, which sets alarm warning for calculations that use matrix elements with virtual external gluons and for lattice renormalization procedures based on their results.