Thu·Sep 19, 2019Thursday·September 19, 2019

1. 01*

   Calculating the five-loop QED contribution to the electron anomalous magnetic moment: Graphs without lepton loops

   Sergey Volkov🇷🇺

   This paper describes a computation of a part of the QED contribution to the electron anomalous magnetic moment that was performed by the author with the help of a supercomputer. The computed part includes all 5-loop QED Feynman graphs without lepton loops. The calculation has led to the result $A_1^{(10)}[\text{no lepton loops}]=6.793(90)$ that is slightly different than the value $7.668(159)$ presented by T. Aoyama, T. Kinoshita, and M. Nio in 2018. The discrepancy is about $4.8\sigma$. The computation gives the first independent check for that value. A shift in the fine-structure constant prediction is revealed in the paper. The developed calculation method is based on (a) a subtraction procedure for removing all ultraviolet and infrared divergences in Feynman parametric space before integration; (b) a nonadaptive Monte Carlo integration that uses the probability density functions that are constructed for each Feynman graph individually using its combinatorial structure. The method is described briefly in the paper (with the corresponding references to the previous papers). The values for the contributions of nine gauge-invariant classes splitting the whole set are presented in the paper. Moreover, the whole set of all 5-loop graphs without lepton loops is split into 807 subsets for comparison (in the future) of the calculated values with the values obtained by another methods. These detailed results are presented in the supplemental materials. Also, the supplemental materials contain the contribution values for each of 3213 individual Feynman graphs. An "oscillating" nature of these values is discussed. Technical details of the realization are described.

   hep-phPRD(2019)·103 citations
2. 02*

   CP-violating Higgs-gauge boson couplings in $H\nu \bar{\nu }$ production at three energy stages of CLIC

   O. Karadeniz🇹🇷 · A. Senol🇹🇷 · K. Y. Oyulmaz🇹🇷 · H. Denizli🇹🇷

   A phenomenological study of CP-violating dimension-six operators via the $e^{+}{e}^{-}\to \nu \bar{\nu }H$ process is performed in a model-independent Standard Model effective field theory framework at all energy stages of CLIC using the updated baseline integrated luminosities. All signal and relevant background events are generated in MadGraph and passed through PYTHIA for parton showering and hadronization at parton level. Detector effects are considered via tuned CLIC detector cards in Delphes. Since we reconstruct the Higgs boson from a pair of b-jets, limits on CP-violating dimension-six couplings are obtained at three $b$-tagging working points: tight, medium and loose defined in the CLIC Delphes card for all three energy stages of CLIC. Our best 95 \% C.L. limits at the loose working point (90 \% b-tagging efficiency) on ${\tilde{c}}_{HW}$ and ${\tilde{c}}_{HB}$ are $[-7.0\times 10^{-3};7.0\times 10^{-3}]$ and $[-3.0\times 10^{-2};3.0\times 10^{-2}]$, respectively at the 3 TeV energy stage of CLIC with an integrated luminosity of 5.0 ab${}^{-1}$. Considering a 0.3 \% systematic uncertainty from possible experimental sources worsens the limits on these couplings by a factor of two.

   hep-phhep-exEPJC(2020)·13 citations
3. 03*

   The Proton Radius Puzzle

   Gil Paz🇺🇸

   In 2010 the proton charge radius was extracted for the first time from muonic hydrogen, a bound state of a muon and a proton. The value obtained was five standard deviations away from the regular hydrogen extraction. Taken at face value, this might be an indication of a new force in nature coupling to muons, but not to electrons. It also forces us to reexamine our understanding of the structure of the proton. Here I describe an ongoing theoretical research effort that seeks to address this "proton radius puzzle". In particular, I will present the development of new effective field theoretical tools that seek to directly connect muonic hydrogen and muon-proton scattering.

   hep-ph5 citations
4. 04*

   Comment on "An improved upper limit on the neutrino mass from a direct kinematic method by KATRIN"

   Alan Chodos🇺🇸

   We note that the central value of the KATRIN measurement has negative mass squared, and wonder why the statistical analysis excludes such values a priori.

   hep-ph0 citations
5. 05*

   Towards a model independent extraction of the Boer-Mulders function

   E. Christova🇧🇬 · D. Kotlorz🇵🇱 · E. Leader🇬🇧

   At present, the Boer-Mulders function for a given quark flavour has been extracted from data on semi-inclusive deep inelastic scattering using the simplifying, but theoretically inconsistent, assumption that it is proportional to the Sivers function for each quark flavour. In this paper, using the latest semi-inclusive deep inelastic COMPASS deuteron data on the $⟨\cos {\varphi }_h⟩$ and $⟨\cos 2{\varphi }_h⟩$ asymmetries we extract the collinear $x_B$-dependence of the Boer-Mulders function for the sum of the valence quarks $Q_V=u_V+d_V$ in an essentially model independent way, and find a significant disagreement with the published results. Our analysis also yields interesting information on the transverse momentum dependence of the unpolarized quark distribution and fragmentation functions.

   hep-ph3 citations
6. 06*

   Mixed QCD$\otimes$QED corrections to on-shell $Z$ boson production at the LHC

   Maximilian Delto🇩🇪 · Matthieu Jaquier🇩🇪 · Kirill Melnikov🇩🇪 · Raoul Röntsch🇨🇭

   We compute the mixed QCD$\otimes$QED corrections to the production of on-shell $Z$ bosons at the LHC at a fully-exclusive level. We also include the factorised NLO QCD correction to $Z$ boson production and NLO QED correction to $Z$ boson decay into two leptons. We make use of an abelianised version of the nested soft-collinear subtraction formalism to perform this computation. We study the phenomenological impact of the mixed QCD$\otimes$QED corrections for a number of observables relevant for LHC phenomenology.

   hep-phJHEP(2020)·75 citations
7. 07*

   Attractive inter-particle force in Van der Waals model of hadron gas in the grand canonical ensemble

   Yaroslav Krivenko-Emetov🇺🇦

   We generalize derivation of partition functions of the grand canonical ensemble for the multicomponent van der Waals gas of interacting particles by hardcore potentials to the case of the attractive large-distance mean field. The formulas obtained by the saddle point method for the thermodynamic potentials with the transparent non-relativistic limit to the case of conserving large number of particles for different gas components like neutrons and protons of nuclear matter can be used for analysis of experimental data for the particle number ratios in nucleus-nucleus collisions at high excitation energies.

   hep-phnucl-th4 citations
8. 08*

   Study of interference effects in the search for flavour-changing neutral current interactions involving the top quark and a photon or a $Z$ boson at the LHC

   Maura Barros🇵🇹 · Nuno Filipe Castro🇵🇹 · Johannes Erdmann🇩🇪 · Gregor Geßner🇩🇪 · Kevin Kröninger🇩🇪 · Salvatore La Cagnina🇩🇪 · Ana Peixoto🇵🇹

   Flavour-changing neutral-current interactions of the top quark can be searched for in top-quark pair production with one top quark decaying to an up-type quark and a neutral boson, and they can be searched for in the single production of a top quark in association with such a boson. Both processes interfere if an additional up-type quark is produced in the case of single production. The impact of these interference effects on searches for flavour-changing neutral currents at the LHC is studied for the case where the neutral boson is a photon or a $Z$ boson. Interference effects are found to be smaller than variations of the renormalisation and factorisation scales.

   hep-phhep-exEur.Phys.J.Plus(2020)·10 citations
9. 09*

   Ward Identities for the Standard Model Effective Field Theory

   Tyler Corbett🇩🇰 · Andreas Helset🇩🇰 · Michael Trott🇩🇰

   We derive Ward identities for the Standard Model Effective Field Theory using the background field method. The resulting symmetry constraints on the Standard Model Effective Field Theory are basis independent, and constrain the perturbative and power-counting expansions. A geometric description of the field connections, and real representations for the $\mathrm{SU}(2{)}_{\mathrm{L}}\times \mathrm{U}(1{)}_{\mathrm{Y}}$ generators, underlies the derivation.

   hep-phPRD(2020)·26 citations
10. 10*

    Generalized Parton Distributions and Pseudo-Distributions

    Anatoly Radyushkin🇺🇸

    We derive one-loop matching relations for the Ioffe-time distributions related to the pion distribution amplitude (DA) and generalized parton distributions (GPDs). They are obtained from a universal expression for the one-loop correction in an operator form, and will be used in the ongoing lattice calculations of the pion DA and GPDs based on the parton pseudo-distributions approach.

    hep-phhep-latPRD(2019)·72 citations
11. 11*

    Inclusive productions of ${\rm Y}(1S,2S,3S)$ and ${\chi }_b(1P,2P,3P)$ via the Higgs boson decay

    Zhan Sun🇨🇳 · Yang Ma🇺🇸

    In this paper, we carry out the complete $\mathcal{O}(\alpha {\alpha }_s^2)$-order study on the inclusive productions of ${\rm Y}(nS)$ and ${\chi }_b(nP)$ ($n=1,2,3$) via the Standard Model Higgs boson decay, within the framework of nonrelativistic QCD. The feeddown effects via the higher excited states are found to be substantial. The color-octet ${}^3{S}_1^{[8]}$ state related processes consisting of $H^0\to b\bar{b}{[}^3{S}_1^{[8]}]+g$ and $H^0\to b\bar{b}{[}^3{S}_1^{[8]}]+Q+\bar{Q}$ ($Q=c,b$) play a vital role in the predictions on the decay widths. Moreover, our newly calculated next-to-leading order QCD corrections to $H^0\to b\bar{b}{[}^3{S}_1^{[8]}]+g$ can enhance its leading-order result by 3-4 times, subsequently magnifying the total ${}^3{S}_1^{[8]}$ contributions by about $40\%$. Such a remarkable enhancement will to a large extent influence the phenomenological conclusions. For the color-singlet ${}^3{P}_J^{[1]}$ state, in addition to $H^0\to b\bar{b}{[}^3{P}_J^{[1]}]+b+\bar{b}$, the newly introduced light hadrons associated process, $H^0\to b\bar{b}{[}^3{P}_J^{[1]}]+g+g$, can also provide non-negligible contributions, especially for ${}^3{P}_2^{[1]}$. Summing up all the contributions, we have ${\mathcal{B}}_{H^0\to {\chi }_b(nP)+X}\sim 10^{-6}-10^{-5}$ and ${\mathcal{B}}_{H^0\to {\rm Y}(nS)+X}\sim 10^{-5}-10^{-4}$, which meets marginally nowadays LHC experimental data and can help in understanding the heavy quarkonium production mechanism as well as the Yukawa couplings.

    hep-phPRD(2019)·7 citations
12. 12*

    New physics in $b\to s\ell \ell$ transitions at one loop

    Rupert Coy🇫🇷 · Michele Frigerio🇫🇷 · Federico Mescia🇪🇸 · Olcyr Sumensari🇮🇹

    We investigate new-physics contributions to $b\to s\ell \ell$ transitions in the context of an effective field theory extension of the Standard Model, including operator mixing at one loop. We identify the few scenarios where a single Wilson coefficient, $C/{\Lambda }^2\sim 1/{\mathrm{TeV}}^2$, induces a substantial shift in the lepton flavour universality ratios $R_K$ and $R_{K^{\ast }}$ at one loop, while evading $Z$-pole precision tests, collider bounds, and other flavour constraints. Good fits to the present data are achieved by a left-handed current operator with quark-flavour indices $(2,2)$ or $(3,3)$, hitherto overlooked. Interestingly, the running of the Standard Model Yukawa matrices gives the dominant effect for these scenarios. We match the favoured effective-theory scenarios to minimal, single-mediator models, which are subject to additional stringent constraints. Notably, we recognise three viable instances of a leptoquark with one coupling to fermions only. If the anomalies were confirmed, it appears that one-loop explanations have good prospects of being directly tested at the LHC.

    hep-phEPJC(2020)·30 citations
13. 13*

    A Standard Model explanation for the excess of electron-like events in MiniBooNE

    A.Ioannisian🇦🇲

    We study the dependence of neutral current (NC) neutrino-induced ${\pi }^0$/photon production (${\nu }_{\mu }+A\to {\nu }_{\mu }+1{\pi }^0/\gamma +X$) on the atomic number of the target nucleus, A, at 4-momentum transfers relevant to the MiniBooNE experiment: $\Delta$ resonance mass region. Our conclusion is based on experimental data for photon-nucleus interactions from the A2 collaboration at the Mainz MAMI accelerator. We work in the approximation that decays of $\Delta$ resonance unaffected by its production channel, via photon or Z boson. $1{\pi }^0+X$ production scales as A${}^{2/3}$, the surface area of the nucleus. Meanwhile the photons created in $\Delta$ decays will leave the nucleus, and that cross section will be proportional to the atomic number of the nucleus. Thus the ratio of photon production to ${\pi }^0$ production is proportional to A${}^{1/3}$. For carbon ${}^{12}$C this factor is $\approx$2.3. MiniBooNE normalises the rate of photon production to the measured ${\pi }^0$ production rate. The reduced neutral pion production rate would yield at least twice as many photons as previously expected, thus significantly lowering the number of unexplained electron-like events.

    hep-ph13 citations
14. 14*

    Probing parton saturation with forward $Z^0$-boson production at small transverse momentum in p+p and p+A collisions

    Cyrille Marquet🇫🇷 · Shu-Yi Wei🇫🇷 · Bo-Wen Xiao🇨🇳

    We calculate and compare the differential cross sections for forward $Z^0$-boson production at small transverse momentum, in proton-proton and proton-nucleus collisions, using both the collinear and dilute-dense factorization frameworks. In both cases, we implement a Sudakov resummation of the large logarithms generated by soft-gluon emissions, which is essential in order to describe the transverse momentum distribution of forward $Z^0$ bosons measured at the Tevatron and the LHC. We further compute the nuclear modification factor in the dilute-dense framework, hoping to single out signals of saturation effects at small values of $x$. Our predictions are compared with those obtained in the collinear factorization framework, using two different nuclear parton distribution functions.

    hep-phhep-exnucl-thPLB(2020)·21 citations
15. 15*

    Tumbling to the Top

    Giacomo Cacciapaglia🇫🇷 · Shahram Vatani🇫🇷 · Zhi-Wei Wang🇩🇰

    We propose a new mechanism to generate the couplings of the top quark to a composite Goldstone Higgs, which we dub {\it Global Extended Technicolor} (GETC). Top, techni-fermions and spin-1 mediators arise as bound states of a tumbling chiral gauge theory. We propose a simple model based on a tumbling $SU(4)$ dynamics, which predicts partial compositeness for the top and an $SU(3)$ model with 6 Dirac flavours for the low-energy composite Higgs. Neutron decay bounds require the new dynamics to confine above $10^{6÷7}$ TeV. A simple extension of the basic model allows to generate partial compositeness also for bottom and tau, and a walking dynamics from an intermediate $SU(3)$ theory with 10 flavours (6 light + 4 heavy), whose dynamics can be studied on the Lattice.

    hep-phhep-lathep-th9 citations
16. 16*

    Direct detection and complementary constraints for sub-GeV dark matter

    Kyrylo Bondarenko🇳🇱 · Alexey Boyarsky🇳🇱 · Torsten Bringmann🇳🇴 · Marco Hufnagel🇩🇪 · Kai Schmidt-Hoberg🇩🇪 · Anastasia Sokolenko🇳🇴

    Traditional direct searches for dark matter, looking for nuclear recoils in deep underground detectors, are challenged by an almost complete loss of sensitivity for light dark matter particles. Consequently, there is a significant effort in the community to devise new methods and experiments to overcome these difficulties, constantly pushing the limits of the lowest dark matter mass that can be probed this way. From a model-building perspective, the scattering of sub-GeV dark matter on nucleons essentially must proceed via new light mediator particles, given that collider searches place extremely stringent bounds on contact-type interactions. Here we present an updated compilation of relevant limits for the case of a scalar mediator, including a new estimate of the near-future sensitivity of the NA62 experiment as well as a detailed evaluation of the model-specific limits from Big Bang nucleosynthesis. We also derive updated and more general limits on DM particles upscattered by cosmic rays, applicable to arbitrary energy- and momentum dependences of the scattering cross section. Finally we stress that dark matter self-interactions, when evaluated beyond the common s-wave approximation, place stringent limits independently of the dark matter production mechanism. These are, for the relevant parameter space, generically comparable to those that apply in the commonly studied freeze-out case. We conclude that the combination of existing (or expected) constraints from accelerators and astrophysics, combined with cosmological requirements, puts robust limits on the maximally possible nuclear scattering rate. In most regions of parameter space these are at least competitive with the best projected limits from currently planned direct detection experiments.

    hep-phastro-ph.COJHEP(2020)·114 citations
17. 17*

    Comment on "A critical look at $\beta$-function singularities at large $N$" by Alanne, Blasi and Dondi

    Francesco Sannino🇩🇰 · Zhi-Wei Wang🇩🇰

    We first briefly review the state-of-the-art of the large $N_f$ gauge-fermion theories and then show that the claim made in the paper by Alanne, Blasi and Dondi that "The singularities in the $\beta$ function and in the fermion mass anomalous dimension are simultaneously removed providing no hint for a UV fixed point in the large-N limit" is unwarranted. This is so since the author's truncation of the beta function violates the large number of matter fields counting.

    hep-phhep-lathep-th3 citations
18. 18*

    What is the amplitude of the Gravitational Waves background expected in the Starobinsky model ?

    Fabrizio Renzi🇮🇹 · Mehdi Shokri🇮🇹 · Alessandro Melchiorri🇮🇹

    The inflationary model proposed by Starobinski in 1979 predicts an amplitude of the spectrum of primordial gravitational waves, parametrized by the tensor to scalar ratio, of $r=0.0037$ in case of a scalar spectral index of $n_S=0.965$. This amplitude is currently used as a target value in the design of future CMB experiments with the ultimate goal of measuring it at more than five standard deviations. Here we evaluate how stable are the predictions of the Starobinski model on $r$ considering the experimental uncertainties on $n_S$ and the assumption of $\Lambda$CDM. We also consider inflationary models where the $R^2$ term in Starobinsky action is generalized to a $R^{2p}$ term with index $p$ close to unity. We found that current data place a lower limit of $r>0.0013$ at $95\%$ C.L. for the classic Starobinski model, and predict also a running of the scalar index different from zero at more than three standard deviation in the range $dn/dlnk=-0.0006_{-0.0001}^{+0.0002}$. A level of gravitational waves of $r\sim 0.001$ is therefore possible in the Starobinski scenario and it will not be clearly detectable by future CMB missions as LiteBIRD and CMB-S4. When assuming a more general $R^{2p}$ inflation we found no expected lower limit on $r$, and a running consistent with zero. We found that current data are able to place a tight constraints on the index of $R^{2p}$ models at $95\%$ C.L. i.e. $p=0.99_{-0.03}^{+0.02}$.

    ↳ astro-ph.COhep-phPhys.Dark Univ.(2020)·24 citations
19. 19*

    EHT constraint on the ultralight scalar hair of the M87 supermassive black hole

    Pedro V.P. Cunha🇵🇹 · Carlos A. R. Herdeiro🇵🇹 · Eugen Radu🇵🇹

    Hypothetical ultralight bosonic fields will spontaneously form macroscopic bosonic halos around Kerr black holes, via superradiance, transferring part of the mass and angular momentum of the black hole into the halo. Such process, however, is only efficient if resonant: when the Compton wavelength of the field approximately matches the gravitational scale of the black hole. For a complex-valued field, the process can form a stationary, bosonic field-black hole equilibrium state - a black hole with synchronised hair. For sufficiently massive black holes, such as the one at the centre of the M87 supergiant elliptic galaxy, the hairy black hole can be robust against its own superradiant instabilities, within a Hubble time. Studying the shadows of such scalar hairy black holes, we constrain the amount of hair which is compatible with the Event Horizon Telescope (EHT) observations of the M87 supermassive black hole, assuming the hair is a condensate of ultralight scalar particles of mass $\mu \sim 10^{-20}$ eV, as to be dynamically viable. We show the EHT observations set a weak constraint, in the sense that typical hairy black holes that could develop their hair dynamically, are compatible with the observations, when taking into account the EHT error bars and the black hole mass/distance uncertainty.

    ↳ gr-qcastro-ph.HEhep-phUniverse(2019)·135 citations
20. 20*

    Flattened Axion Monodromy Beyond Two Derivatives

    Francisco G. Pedro🇮🇹 · Alexander Westphal🇩🇪

    We study string inspired two-field models of large-field inflation based on axion monodromy in the presence of an interacting heavier modulus. This class of models has enough structure to approximate at least part of the backreaction effects known in full string theory, such as kinetic mixing with the axion, and flattening of the scalar potential. Yet, it is simple enough to fully describe the structure of higher-point curvature perturbation interactions driven by the adjusting modulus backreaction dynamics. We find that the presence of the heavy modulus can be described via two equivalent effective field theories, both of which can incorporate reductions of the speed of sound. Hence, the presence of heavier moduli in axion monodromy inflation constructions will necessarily generate some amount of non-Gaussianity accompanied by changes to $n_s$ and $r$ beyond what results from just from the well known adiabatic flattening backreaction.

    ↳ hep-thastro-ph.COhep-phPRD(2020)·8 citations
21. 21*

    Pion Valence Structure from Ioffe Time Pseudo-Distributions

    Bálint Joó🇺🇸 · Joseph Karpie🇺🇸 · Kostas Orginos🇺🇸 · Anatoly V. Radyushkin🇺🇸 · David G. Richards🇺🇸 · Raza Sabbir Sufian🇺🇸 · Savvas Zafeiropoulos🇩🇪

    We present a calculation of the pion valence quark distribution extracted using the formalism of reduced Ioffe time pseudo-distributions or more commonly known as pseudo-PDFs. Our calculation is carried out on two different 2+1 flavor QCD ensembles using the isotropic-clover fermion action, with lattice dimensions $24^3\times 64$ and $32^3\times 96$ at the lattice spacing of $a=0.127$ fm, and with the quark mass equivalent to a pion mass of $m_{\pi }\simeq 415$ MeV. We incorporate several combinations of smeared-point and smeared-smeared pion source-sink interpolation fields in obtaining the lattice QCD matrix elements using the summation method. After one-loop perturbative matching and combining the pseudo-distributions from these two ensembles, we extract the pion valence quark distribution using a phenomenological functional form motivated by the global fits of parton distribution functions. We also calculate the lowest four moments of the pion quark distribution through the "OPE without OPE". We present a qualitative comparison between our lattice QCD extraction of the pion valence quark distribution with that obtained from global fits and previous lattice QCD calculations.

    ↳ hep-lathep-phnucl-exnucl-thPRD(2019)·159 citations
22. 22*

    Matter Wave Interferometry for Inertial Sensing and Tests of Fundamental Physics

    D. Schlippert🇩🇪 · C. Meiners🇩🇪 · R.J. Rengelink🇩🇪 · C. Schubert🇲🇽 · D. Tell🇩🇪 · E. Wodey🇩🇪 · K.H. Zipfel🇩🇪 · W. Ertmer🇩🇪 · E.M. Rasel🇩🇪

    Very Long Baseline Atom Interferometry (VLBAI) corresponds to ground-based atomic matter-wave interferometry on large scales in space and time, letting the atomic wave functions interfere after free evolution times of several seconds or wave packet separation at the scale of meters. As inertial sensors, e.g., accelerometers, these devices take advantage of the quadratic scaling of the leading order phase shift with the free evolution time to enhance their sensitivity, giving rise to compelling experiments. With shot noise-limited instabilities better than $10^{-9}$ m/s${}^2$ at 1 s at the horizon, VLBAI may compete with state-of-the-art superconducting gravimeters, while providing absolute instead of relative measurements. When operated with several atomic states, isotopes, or species simultaneously, tests of the universality of free fall at a level of parts in $10^{13}$ and beyond are in reach. Finally, the large spatial extent of the interferometer allows one to probe the limits of coherence at macroscopic scales as well as the interplay of quantum mechanics and gravity. We report on the status of the VLBAI facility, its key features, and future prospects in fundamental science.

    ↳ physics.atom-phhep-ph15 citations
23. 23*

    Near-Conformal Dynamics at Large Charge

    Domenico Orlando🇮🇹 · Susanne Reffert🇨🇭 · Francesco Sannino🇩🇰

    We investigate four-dimensional near-conformal dynamics by means of the large-charge limit. We first introduce and justify the formalism in which near-conformal invariance is insured by adding a dilaton and then determine the large-charge spectrum of the theory. The dilaton can also be viewed as the radial mode of the EFT. We calculate the two-point functions of charged operators. We discover that the mass of the dilaton, parametrising the near-breaking of conformal invariance, induces a novel term that is logarithmic in the charge. One can therefore employ the large-charge limit to explore near-conformal dynamics and determine dilaton-related properties.

    ↳ hep-thhep-lathep-phPRD(2020)·34 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.