Mon·Jul 10, 2023Monday·July 10, 2023

1. 01*

   Triangle singularity in the $J/\psi \to \gamma \bar{p}\Delta$ decay

   Ke Wang🇨🇳 · Rong Li🇨🇳 · Bo-Chao Liu🇨🇳

   In this work, we study the role of triangle singularity in the $J/\psi \to \gamma \bar{p}\Delta$ decay. We find that through a triangle mechanism, involving a triangle loop composed by $\omega$, $\pi$ and $p$, this decay may develop a triangle singularity and produce a visible peak in the invariant mass $M_{\gamma \Delta }$ around 1.73 GeV with a width of 0.02 GeV. Such a triangle mechanism may also cause significant spin effects on the final $\Delta$, which can be detected by measuring its spin density matrix elements. Our calculations show that the branching ratios due to the triangle mechanism is Br($J/\psi \to \gamma \bar{p}\Delta ,\Delta \to \pi p$)=$1.058\times 10^{-6}$. Hopefully, this reaction can be investigated at BESIII and future experiments, e.g. Super Tau-Charm Facility, and the narrow width of the induced structure, the moving TS position and the distinct features of the spin density matrix elements of the $\Delta$ may serve as signals for the triangle singularity mechanism.

   hep-phPRD(2023)·7 citations
2. 02*

   Modular flavor symmetric models

   Tatsuo Kobayashi🇯🇵 · Morimitsu Tanimoto🇯🇵

   We review the modular flavor symmetric models of quarks and leptons focusing on our works. We present some flavor models of quarks and leptons by using finite modular groups and discuss the phenomenological implications. The modular flavor symmetry gives interesting phenomena at the fixed point of modulus. As a representative, we show the successful texture structure at the fixed point $\tau =\omega$. We also study CP violation, which occurs through the modulus stabilization. Finally, we study SMEFT with modular flavor symmetry by including higher dimensional operators.

   hep-phInt.J.Mod.Phys.A(2024)·105 citations
3. 03*

   Exploration of possible signals beyond special relativity using high-energy astroparticle physics

   Maykoll A. Reyes🇪🇸

   To unify the standard model of particle physics and general relativity, we may require a quantum description of gravity, which will change our notion of spacetime at very high energies. In this dissertation we explore possible traces of new physics beyond special relativity, using the propagation of high energy astroparticles. For this purpose, the two ways of going beyond Lorentz invariance are presented, a breaking of the Lorentz invariance (Lorentz invariance violation or LIV or its deformation (doubly special relativity or DSR), emphasizing their conceptual and phenomenological differences. For the study of LIV, the work focuses on the prediction of modifications in the expected neutrino flux on Earth, both from astrophysical and cosmogenic origin (from the interaction of cosmic rays with the background radiation during their propagation). For the study of DSR we focus instead on the search for anomalies in the time of flight of massless particles (time delays) and on the study of the expected flux of gamma rays on Earth. The results obtained show the possibility of using astroparticle observations as a window to quantum gravity phenomenology, at energies attainable at present and/or in the very near future.

   hep-phastro-ph.HEgr-qc3 citations
4. 04*

   Estimates of absolute branching fractions for the $f_0(1710)$ decays and radiative transitions $\psi (2S)\to \gamma f_0(1710)$ and ${\rm Y}(1S)\to \gamma f_0(1710)$

   N.N. Achasov🇷🇺 · G.N. Shestakov🇷🇺

   Using the result of the VES Collaboration for $Br(J/\psi \to \gamma f_0(1710))$, we estimate the absolute branching fractions for the $f_0(1710)$ decays into $\pi \pi$, $K\bar{K}$, $\eta \eta$, $\omega \omega$, and $\omega \varphi$. In addition, we estimate $Br(\psi (2S)\to \gamma f_0(1710))\approx 3.5\times 10^{-5}$ and $Br({\rm Y}(1S)\to \gamma f_0(1710))\approx 1\times 10^{-5}$.

   hep-phhep-exnucl-exnucl-thJETP Lett.(2023)·1 citation
5. 05*

   New Early Dark Energy as a solution to the $H_0$ and $S_8$ tensions

   Florian Niedermann🇸🇪 · Martin S. Sloth🇩🇰

   New Early Dark Energy introduces a new phase of dark energy that decays in a fast-triggered phase transition around matter-radiation equality. The presence of a trigger mechanism sets it apart from other early dark energy models. Here, we will argue that New Early Dark Energy offers a simple and natural framework to extend $\Lambda$CDM while also providing a pathway to resolving the $H_0$ tension alongside its smaller cousin, the $S_8$ tension. At the microscopic level, we discuss the possibility that the trigger is either given by an ultralight scalar field or a dark sector temperature. In both cases, it prompts the transition of an $\mathrm{eV}$-mass scalar field from its false to its true minimum. Furthermore, we argue that the same phase transition could give rise to a dynamic process for generating neutrino masses.

   hep-phastro-ph.COhep-thHubble Constant Tension: Springer(2024)·37 citations
6. 06*

   Signatures of afterglows from light dark matter boosted by supernova neutrinos in current and future large underground detectors

   Yen-Hsun Lin🇹🇼 · Tsung-Han Tsai🇹🇼 · Guey-Lin Lin🇹🇼 · Henry Tsz-King Wong🇹🇼 · Meng-Ru Wu🇹🇼

   Supernova neutrino boosted dark matter (SN$\nu$ BDM) and its afterglow effect have been shown to be a promising signature for beyond Standard Model (bSM) physics. The time-evolution feature of SN$\nu$ BDM allows for %the possibly direct inference of DM mass $m_{\chi }$, and results in significant background suppression with improving sensitivity. This paper extends the earlier study and provides a general framework for computing the SN$\nu$ BDM fluxes for a supernova that occurs at any location in our galaxy. A bSM $U(1{)}_{L_{\mu }-L_{\tau }}$ model with its gauge boson coupling to both DM and the second and third generation of leptons is considered, which allows for both DM-$\nu$ and DM-$e$ interactions. Detailed analysis of the temporal profile, angular distribution, and energy spectrum of the SN$\nu$ BDM are performed. Unique signatures in SN$\nu$ BDM allowing extraction of $m_{\chi }$ and detail features that contain information of the underlying interaction type are discussed. Expected sensitivities on the above new physics model from Super-Kamiokande, Hyper-Kamiokande, and DUNE detections of BDM events induced by the next galactic SN are derived and compared with the existing bounds.

   hep-phastro-ph.COastro-ph.HEPRD(2023)·17 citations
7. 07*

   Electron-positron, parton-parton and photon-photon production of $\tau$-lepton pairs: anomalous magnetic and electric dipole moments spin effects

   Sw. Banerjee🇺🇸 · A.Yu. Korchin🇺🇦 · E. Richter-Was🇵🇱 · Z. Was🇵🇱

   Anomalous contributions to the electric and magnetic dipole moments of the $\tau$ lepton from new physics scenarios have brought renewed interest in the development of new charge-parity violating signatures in $\tau$-pair production at Belle II energies, and also at higher energies of the Large Hadron Collider and the Future Circular Collider. In this paper, we discuss the effects of spin correlations, including transverse degrees of freedom, in the $\tau$-pair production and decay. These studies include calculating analytical formulas, obtaining numerical results, and building semi-realistic observables sensitive to the transverse spin correlations induced by the dipole moments of the $\tau$ lepton. The effects of such anomalous contributions to the dipole moments are introduced on top of precision simulations of $e^{-}{e}^{+}\to {\tau }^{-}{\tau }^{+}$, $q\bar{q}\to {\tau }^{-}{\tau }^{+}$ and $\gamma \gamma \to {\tau }^{-}{\tau }^{+}$ processes, involving multi-body final states. The $\tau$ decays are simulated along with radiative corrections, in particular electroweak box contributions of $WW$ and $ZZ$ exchanges are taken into account. Respective extensions of the Standard Model amplitudes and the reweighting algorithms are implemented into the KKMC Monte Carlo, which is used to simulate $\tau$-pair production in $e^{-}{e}^{+}$ collisions, and the TauSpinner program, which is used to reweight events with $\tau$ pair produced in $pp$ collisions.

   hep-phPRD(2024)·14 citations
8. 08*

   SN1987A and neutrino non-radiative decay

   Pilar Iváñez-Ballesteros (APC, Paris)🇫🇷 · M. Cristina Volpe (APC, Paris)🇫🇷

   We investigate neutrino non-radiative two-body decay in vacuum, in relation to SN1987A. In a full $3\nu$ decay framework, we perform a detailed likelihood analysis of the 24 neutrino events from SN1987A observed by Kamiokande-II, IMB, and Baksan. We consider both normal and inverted neutrino mass orderings, and the possibility of strongly hierarchical and quasi-degenerate neutrino mass patterns. The results of the likelihood analysis show that the sensitivity is too low to derive bounds in the case of normal mass ordering. On the contrary, in the case of inverted mass ordering we obtain the bound $\tau /m\ge 2.4\times 10^5$ s/eV ($1.2\times 10^5$) s/eV at 68 $\%$ (90 $\%$) CL on the lifetime-to-mass ratio of the mass eigenstates ${\nu }_2$ and ${\nu }_1$.

   hep-phastro-ph.HEastro-ph.SRhep-exPLB(2023)·27 citations
9. 09*

   New physics analysis of ${\Lambda }_b\to ({\Lambda }^{\ast }(\to p{K}^{-}),\Lambda (\to p\pi ))({\mu }^{+}{\mu }^{-},\nu \bar{\nu })$ baryonic decays under SMEFT framework

   Nilakshi Das🇮🇳 · Rupak Dutta🇮🇳

   The di-leptons and di-neutrinos observed in the final states of flavor-changing neutral b decays provide an ideal platform for probing physics beyond the standard model. Although the latest measurements of $R_{K^{(\ast )}}$ agree well with the standard model prediction, there exists several other observables such as $P_5^{\prime }$, $\mathcal{B}(B_s\to \varphi {\mu }^{+}{\mu }^{-})$ and $\mathcal{B}(B_s\to {\mu }^{+}{\mu }^{-})$ in $b\to s\ell \ell$ transition decays that shows deviation from the standard model prediction. Similalry, very recently Belle II collaboration reported a more precise upper bound of $\mathcal{B}(B\to K^{+}\nu \bar{\nu })<4.1\times 10^{-5}$ by employing a new inclusive tagging approach and it also deviates from the standard model expectation. The $b\to s{l}^{+}{l}^{-}$ and $b\to s\nu \bar{\nu }$ transition decays are related not only in the standard model but also in beyond the standard model physics due to $SU(2{)}_L$ gauge symmetry, and can be most effectively investigated using the standard model effective field theory formalism. Additionally, the $b\to s\nu \bar{\nu }$ decay channels are theoretically cleaner than the corresponding $b\to s{l}^{+}{l}^{-}$ decays, as these processes do not get contributions from non-factorizable corrections and photonic penguin contributions. In this context, we study ${\Lambda }_b\to ({\Lambda }^{\ast }(\to p{K}^{-}),\Lambda (\to p\pi ))({\mu }^{+}{\mu }^{-},\nu \bar{\nu })$ baryonic decays undergoing $b\to s{\ell }^{+}{\ell }^{-}$ and $b\to s\nu \bar{\nu }$ quark level transitions in a standard model effective field theory formalism. We give predictions of several observables pertaining to these decay channels in the standard model and in case of several new physics scenarios.

   hep-phPRD(2023)·18 citations
10. 10*

    Recent progress on in-medium properties of heavy mesons from finite-temperature EFTs

    Gloria Montana🇺🇸 · Angels Ramos🇪🇸 · Laura Tolos🇪🇸 · Juan M. Torres-Rincon🇪🇸

    Mesons with heavy flavor content are an exceptional probe of the hot QCD medium produced in heavy-ion collisions. In the past few years, significant progress has been made toward describing the modification of the properties of heavy mesons in the hadronic phase at finite temperature. Ground-state and excited-state thermal spectral properties can be computed within a self-consistent many-body approach that employs appropriate hadron-hadron effective interactions, providing a unique opportunity to confront hadronic Effective Field Theory predictions with recent and forthcoming lattice QCD simulations and experimental data. In this article, we revisit the application of the imaginary-time formalism to extend the calculation of unitarized scattering amplitudes from the vacuum to finite temperature. These methods allow us to obtain the ground-state thermal spectral functions. The thermal properties of the excited states that are dynamically generated within the molecular picture are also directly accessible. We present here the results of this approach for the open-charm and open-bottom sectors. We also analyze how the heavy-flavor transport properties, which are strongly correlated to experimental observables in heavy-ion collisions, are modified in hot matter. In particular, transport coefficients can be computed using an off-shell kinetic theory that is fully consistent with the effective theory describing the scattering processes. The results of this procedure for both charm and bottom transport coefficients are briefly discussed.

    hep-phnucl-thFront.in Phys.(2023)·8 citations
11. 11*

    Low Scale Seesaw with Local Lepton Number

    Hridoy Debnath🇺🇸 · Pavel Fileviez Perez🇺🇸

    We discuss a class of theories for Majorana neutrinos where the total lepton number is a local gauge symmetry. These theories predict a dark matter candidate from anomaly cancellation. We discuss the properties of the dark matter candidate and using the cosmological bounds, we obtain the upper bound on the lepton number symmetry breaking scale. The dark matter candidate has unique annihilation channels due to the fact that the theory predicts a light pseudo-Goldstone boson, the Majoron, and one can obtain the correct relic density in a large fraction of the parameter space. In this context, the seesaw scale is below the $\mathcal{O}(10^2)$TeV scale and one can hope to test the origin of neutrino masses at current or future colliders. We discuss the lepton number violating Higgs decays and the possibility to observe lepton number violation at the Large Hadron Collider.

    hep-phhep-exPRD(2023)·8 citations
12. 12*

    Pion quasiparticles in isospin medium from holography

    Weijian Liang🇨🇳 · Xuanmin Cao🇨🇳 · Hui Liu🇨🇳 · Danning Li🇨🇳

    The properties of the pion quasiparticle in hot and dense isospin medium, including the temperature and isospin chemical potential dependence of their screening mass, pole mass and thermal width, as well as their relationships with the pion superfluid phase transition, are investigated in the framework of two-flavor ($N_f=2$) soft-wall AdS/QCD models. We extract the screening mass of the pion from the pole of the spatial two-point Retarded correlation function. We find that the screening masses of both neutral and charged pions increase monotonously with the increasing of temperature. However, the isospin chemical potential ${\mu }_I$ would depress the screening masses of the charged pions, $m_{{\pi }^{\pm },\mathrm{scr}}$. With the increasing of ${\mu }_I$, $m_{{\pi }^{\pm },\mathrm{scr}}$ monotonically decrease to zero on the boundary between the normal phase and the pion superfluid phase, while the screening mass of the neutral pion, $m_{{\pi }^0,\mathrm{scr}}$, remains almost unchanged. The pole mass $m_{\mathrm{pole}}$ and thermal width $\Gamma$ of the pion are extracted from the pole of temporal two-point Retarded correlation function, i.e., the corresponding quasi-normal frequencies, $\omega =m_{\mathrm{pole}}-i\Gamma /2$. The results show that the pole masses of the three modes (${\pi }^0,{\pi }^{+},{\pi }^{-}$) are splitting at finite ${\mu }_I$. The thermal widths of the three modes monotonically increase with temperature. Furthermore, the pole mass of ${\pi }^{+}$ decreases almost linearly with the increasing of ${\mu }_I$ and reaches zero at ${\mu }_I={\mu }_I^c$, It means that ${\pi }^{+}$ becomes a massless Goldstone boson of the pion superfluid phase transition.

    hep-phhep-thPRD(2023)·5 citations
13. 13*

    Challenges in Interpreting the NANOGrav 15-Year Data Set as Early Universe Gravitational Waves Produced by ALP Induced Instability

    Michael Geller🇮🇱 · Subhajit Ghosh🇺🇸 · Sida Lu🇨🇳 · Yuhsin Tsai🇺🇸

    In this paper, we study a possible early universe source for the recent observation of a stochastic gravitational wave background at the NANOGrav pulsar timing array. The source is a tachyonic instability in a dark gauge field induced by an axion-like particle (ALP), a known source for gravitational waves. We find that relative to the previous analysis with the NANOGrav 12.5-year data set, the current 15-year data set favors parameter space with a relatively larger axion mass and decay constant. This favored parameter space is heavily constrained by $\Delta N_{\mathrm{eff}}$ and overproduction of ALP dark matter. While there are potential mechanisms for avoiding the second problem, evading the $\Delta N_{\mathrm{eff}}$ constraint remains highly challenging. In particular, we find that the gravitational wave magnitude is significantly suppressed with respect to the gauge boson dark radiation, which implies that successfully explaining the NANOGrav observation requires a large additional dark radiation, violating the cosmological constraints. Satisfying the $\Delta N_{\mathrm{eff}}$ constraint will limit the potential contribution from this mechanism to the observed signal to at most a percent level.

    hep-phastro-ph.COastro-ph.HEPRD(2024)·32 citations
14. 14*

    Confronting the 95 GeV excesses within the UN2HDM

    J. A. Aguilar-Saavedra🇪🇸 · H. B. Câmara🇵🇹 · F. R. Joaquim🇵🇹 · J. F. Seabra🇪🇸

    We consider the small excesses around 95 GeV found in several searches for a new scalar in $\gamma \gamma$, $\tau \tau$ and $b\bar{b}$ final states. Instead of trying to accommodate them all, as is usually done in the literature, in the context of a given Standard Model~(SM) extension, we investigate whether it would be possible that one or two of these excesses correspond to an actual new scalar, while the remaining ones are merely statistical fluctuations. To this end, we use as benchmark model the UN2HDM, a SM extension with one scalar doublet, one scalar singlet, and an extra $\text{U}(1{)}^{\prime }$ symmetry, which has been previously studied in the context of multiboson cascade decays. We show that most of the possibilities where the excesses in one or two of these channels disappear in the future can be accommodated by type-I or type-III UN2HDMs.

    hep-phhep-exPRD(2023)·57 citations
15. 15*

    Spectroscopy and femtoscopic correlation function of the $B\bar{D}$, $B=(N,\Delta )$ system in quark delocalization color screening model

    Xuejie Liu · Dianyong Chen · Hongxia Huang · Jialun Ping

    In this work, we systematically investigate the pentaquark systems with quark contents $qqqq\bar{c}$ with the analyzed total spin and parity quantum numbers of $J^P={\frac{1}{2}}^{-}$, $J^P={\frac{3}{2}}^{-}$ and $J^P={\frac{5}{2}}^{-}$, in the I=0, I=1 and I=2 isospin channels. The effective potentials between baryon and meson clusters are given, and the possible bound states are also investigated. Also, the study of the scattering process of the open channels is performed to identify possible resonance states. Our estimations indicate that several possible bound states and narrow baryon-meson resonances are found from corresponding the calculation processes. Furthermore, to bridge the gap between theoretical predictions and experimental measurement, we also extract the low-energy scattering parameters and compute the femtoscopic correlation functions for the $N\bar{D}$ system using the CATS framework. The results demonstrate that the predicted $I=0$ bound state manifests as a significant enhancement at low momentum accompanied by a characteristic suppression. In contrast, the $I=1$ correlations remain relatively flat as the predicted resonances are kinematically distant from the threshold. The $I=2$ sector exhibits strong spin dependence, where the bound state signal in the $J=1/2^{-}$ channel is largely masked by repulsive components in spin-averaged observables. This cancellation effect suggests that future experimental searches at ALICE and LHCb may require spin-selective measurements to identify such states. These predictions provide crucial theoretical guidance for future experiments.

    hep-phnucl-th2 citations
16. 16*

    Single field inflation in the light of Pulsar Timing Array Data: Quintessential interpretation of blue tilted tensor spectrum through Non-Bunch Davies initial condition

    Sayantan Choudhury🇮🇳

    In this work, we present a quintessential interpretation of having a blue-tilted tensor power spectrum for canonical single-field slow-roll inflation to explain the recently observed Pulsar Timing Array (NANOGrav 15-year and EPTA) signal of Gravitational Waves (GW). We formulate the complete semi-classical description of cosmological perturbation theory in terms of scalar and tensor modes using the Non-Bunch Davies initial condition. We found that the existence of the blue tilt ($n_t$) within the favoured range $1.2<n_t<2.5$ can be explained in terms of a newly derived consistency relation. Further, we compute a new field excursion formula using the Non-Bunch Davies initial condition, that validates the requirement of Effective Field Theory in the sub-Planckian regime, $|\Delta \varphi |\ll M_{\mathrm{pl}}$ for the allowed value of the tensor-to-scalar ratio, $r<0.06$ from CMB observations. In our study, we refer to this result as Anti Lyth bound as it violates the well-known Lyth bound originally derived for Bunch Davies initial condition. Further, we study the behaviour of the spectral density of GW and the associated abundance with the frequency, which shows that within the frequency domain $10^{-9}\mathrm{Hz}<f<10^{-7}\mathrm{Hz}$ the outcome obtained from our analysis is completely consistent with the Pulsar Timing Array (NANOGrav 15-year and EPTA) signal. Also, we found that the behaviour of GW spectra satisfies the CMB constraints at the low frequency, $f_{\ast }\sim 7.7\times 10^{-17}\mathrm{Hz}$ corresponding to the pivots scale wave number, $k_{\ast }\sim 0.05{\mathrm{Mpc}}^{-1}$. Finally, the sharp falling behaviour of the GW spectra within the frequency domain $10^{-7}\mathrm{Hz}<f<1\mathrm{Hz}$ validates our theory in the comparatively high-frequency regime as well.

    ↳ astro-ph.COgr-qchep-phhep-thEPJC(2024)·93 citations
17. 17*

    Atomic screening and $e^{+}{e}^{-}$ pair photoproduction at low energies

    P.A. Krachkov🇷🇺 · A.I. Milstein🇷🇺

    The effect of screening by atomic electrons on the behavior of electron and positron wave functions in the continuous spectrum at small distances is studied. It is shown that these asymptotics are affected not only by the static potential of atomic electrons, but also by the polarization potential, as well as by the exchange interaction, which is essential for nonrelativistic electrons. A simple analytical expression is obtained for the photoproduction cross section of $e^{+}{e}^{-}$ pair in an atomic field near the threshold. The spectrum and angular distribution of the produced particles are considered. It is shown that screening significantly affects the cross section in the near-threshold region.

    ↳ physics.atom-phhep-phPLB(2023)·2 citations
18. 18*

    The backreaction effect of the sound speed resonance in DBI inflation

    Bichu Li🇨🇳 · Chao Chen🇨🇳 · Bo Wang🇨🇳

    We examine the backreaction effect of the enhanced small-scale scalar perturbations from the sound speed resonance (SSR) mechanism for primordial black hole formation in Dirac-Born-Infeld (DBI) inflation on background as well as curvature perturbation, which can generate a considerable amount of primordial black holes (PBH) in the radiation-dominated epoch. Within the perturbative regime, the backreaction effect of perturbations on the background dynamics can be described by an effective action after integrating out the perturbation sector. Starting with the effective field theory of a specific DBI inflation model that incorporates SSR, we obtain the one-loop effective action by integrating out the scalar perturbations at the quadratic level. Using the effective Friedmann equations derived from this one-loop effective action, we solve the Hubble parameter with backreaction and the effective perturbation dynamics on this background as well. Our numerical findings reveal that, for a viable parameter space, the backreaction effect results in a relative correction to the Hubble parameter of approximately $10^{-7}$, whereas the relative correction to the slow-roll parameter can vary between $-0.3$ and $0.1$, before gradually converging to $10^{-7}$. Furthermore, our results show that the backreaction effect on SSR sound speed causes a slight reduction in the resonant peak of the curvature power spectrum, and the subsequent PBH formation predicted by the SSR mechanism remains almost unchanged.

    ↳ astro-ph.COgr-qchep-phhep-thPLB(2024)·6 citations
19. 19*

    Ricci Reheating Reloaded

    Giorgio Laverda🇵🇹 · Javier Rubio🇪🇸

    A Hubble-induced phase transition is a natural spontaneous symmetry breaking mechanism allowing for explosive particle production in non-oscillatory models of inflation involving non-minimally coupled spectator fields. In this work, we perform a comprehensive characterisation of this type of transitions as a tachyonic Ricci-heating mechanism, significantly extending previous results in the literature. By performing $\mathcal{O}(100)$ 3+1-dimensional classical lattice simulations, we explore the parameter space of two exemplary scenarios, numerically determining the main timescales in the process. Based on these results, we formulate a set of parametric equations that offer a practical approach for determining the efficiency of the heating process, the temperature at the onset of radiation domination, and the minimum number of e-folds of inflation needed to resolve the flatness and horizon problems in specific quintessential inflation scenarios. These parametric equations eliminate the need for additional lattice simulations, providing a convenient and efficient method for evaluating these key quantities.

    ↳ astro-ph.COgr-qchep-phJCAP(2024)·47 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.