Thu·Feb 18, 2021Thursday·February 18, 2021

1. 01*

   Terrestrial Probes of Electromagnetically Interacting Dark Radiation

   Jui-Lin Kuo🇦🇹 · Maxim Pospelov🇺🇸 · Josef Pradler🇦🇹

   We study the possibility that dark radiation, sourced through the decay of dark matter in the late Universe, carries electromagnetic interactions. The relativistic flux of particles induces recoil signals in direct detection and neutrino experiments through its interaction with millicharge, electric/magnetic dipole moments, or anapole moment/charge radius. Taking the DM lifetime as 35 times the age of the Universe, as currently cosmologically allowed, we show that direct detection (neutrino) experiments have complementary sensitivity down to $ϵ\sim 10^{-11}$ $(10^{-12})$, $d_{\chi }/{\mu }_{\chi }\sim 10^{-9}{\mu }_B$ $(10^{-13}{\mu }_B)$, and $a_{\chi }/b_{\chi }\sim 10^{-2}{\mathrm{GeV}}^{-2}$ $(10^{-8}{\mathrm{GeV}}^{-2})$ on the respective couplings. Finally, we show that such dark radiation can lead to a satisfactory explanation of the recently observed XENON1T excess in the electron recoil signal without being in conflict with other bounds.

   hep-phastro-ph.COPRD(2021)·8 citations
2. 02*

   Jet quenching in expanding medium

   Souvik Priyam Adhya🇨🇿 · Carlos A. Salgado🇪🇸 · Martin Spousta🇨🇿 · Konrad Tywoniuk🇳🇴

   Comprehensive understanding of medium-induced radiative energy loss is of a paramount importance in describing observed jet quenching in heavy-ion collisions. In this work, we have calculated the medium-modified gluon splitting rates for different profiles of the expanding partonic medium, namely profiles for static, exponential, and Bjorken expanding medium. Here in this study, we have used the Baier-Dokshitzer-Mueller-Peigne-Schiff-Zakharov (BDMPSZ) formalism for multiple soft scatterings with a time-dependent transport coefficient for characterizing the expanding medium. Using the kinetic rate equation, we have numerically evaluated the distribution of the medium evolved gluon spectra for different medium profiles. We have presented a calculation of the jet $Q_{AA}$ which quantifies a sensitivity of the inclusive jet suppression on the way how the medium expands. Comparisons of predicted jet $Q_{AA}$ with experimental data from the LHC are also presented.

   hep-phPhys.Scripta(2021)·1 citation
3. 03*

   Possible studies at the first stage of the NICA collider operation with polarized and unpolarized proton and deuteron beams

   V.V. Abramov🇷🇺 · A. Aleshko🇷🇺 · V.A. Baskov🇷🇺 · E.Boos🇷🇺 · V.Bunichev🇷🇺 · O.D. Dalkarov🇷🇺 · R. El-Kholy🇪🇬 · A. Galoyan🇷🇺 · A.V. Guskov🇷🇺 · V.T. Kim🇷🇺 · E. Kokoulina🇷🇺 · I.A. Koop🇷🇺 and 23 other authors

   This paper contains suggestions for experiments with usage of the Spin Physics Detector (SPD) at the first stage of the SPD NICA Programme developing at JINR. Double polarized pp-, dd- and pd- collisions at c.m.s. NN energies of 3.4-10 GeV, which will be accessible at the initial stage of experiments, allow one to study spin dependence of the NN interaction, search for multiquark states at double strangeness, charm and beauty thresholds, study the short-range structure of the deuteron. Double polarized pd scattering offer a possibility to test the Standard Model through the search for T-invariance violation.

   hep-phhep-exPhys.Part.Nucl.(2021)·59 citations
4. 04*

   Scalar and fermion on-shell amplitudes in generalized Higgs effective field theory

   Ryo Nagai🇮🇹 · Masaharu Tanabashi🇯🇵 · Koji Tsumura🇯🇵 · Yoshiki Uchida🇯🇵

   Beyond standard model (BSM) particles should be included in effective field theory in order to compute the scattering amplitudes involving these extra particles. We formulate an extension of Higgs effective field theory which contains arbitrary number of scalar and fermion fields with arbitrary electric and chromoelectric charges. The BSM Higgs sector is described by using the non-linear sigma model in a manner consistent with the spontaneous electroweak symmetry breaking. The chiral order counting rule is arranged consistently with the loop expansion. The leading order Lagrangian is organized in accord with the chiral order counting rule. We use a geometrical language to describe the particle interactions. The parametrization redundancy in the effective Lagrangian is resolved by describing the on-shell scattering amplitudes only with the covariant quantities in the scalar/fermion field space. We introduce a useful coordinate (normal coordinate), which simplifies the computations of the on-shell amplitudes significantly. We show the high energy behaviors of the scattering amplitudes determine the "curvature tensors" in the scalar/fermion field space. The massive spinor-wavefunction formalism is shown to be useful in the computations of on-shell helicity amplitudes.

   hep-phhep-thPRD(2021)·5 citations
5. 05*

   $D{\bar{D}}^{\ast }$ scattering and ${\chi }_{c1}(3872)$ in nuclear matter

   M. Albaladejo🇺🇸 · J. M. Nieves🇪🇸 · L. Tolos🇪🇸

   We study the behaviour of the ${\chi }_{c1}(3872)$, also known as $X(3872)$, in dense nuclear matter. We begin from a picture in vacuum of the $X(3872)$ as a purely molecular $(D{\bar{D}}^{\ast }-c.c.)$ state, generated as a bound state from a heavy-quark symmetry leading-order interaction between the charmed mesons, and analyze the $D{\bar{D}}^{\ast }$ scattering $T-$matrix ($T_{D{\bar{D}}^{\ast }}$) inside of the medium. Next, we consider also mixed-molecular scenarios and, in all cases, we determine the corresponding $X(3872)$ spectral function and the $D{\bar{D}}^{\ast }$ amplitude, with the mesons embedded in the dense environment. We find important nuclear corrections for $T_{D{\bar{D}}^{\ast }}$ and the pole position of the resonance, and discuss the dependence of these results on the $D{\bar{D}}^{\ast }$ molecular component in the $X(3872)$ wave-function. These predictions could be tested in the finite-density regime that can be accessed in the future CBM and PANDA experiments at FAIR.

   hep-phhep-exhep-thnucl-ex+1PRC(2021)·23 citations
6. 06*

   Analyticity and Regge asymptotics in virtual Compton scattering on the nucleon

   Irinel Caprini🇷🇴

   We test the consistency of the data on the nucleon structure functions with analyticity and the Regge asymptotics of the virtual Compton amplitude. By solving a functional extremal problem, we derive an optimal lower bound on the maximum difference between the exact amplitude and the dominant Reggeon contribution for energies $\nu$ above a certain high value ${\nu }_h(Q^2)$. Considering in particular the difference of the amplitudes $T_1^{\text{inel}}(\nu ,Q^2)$ for the proton and neutron, we find that the lower bound decreases in an impressive way when ${\nu }_h(Q^2)$ is increased, and represents a very small fraction of the magnitude of the dominant Reggeon. While the method cannot rule out the hypothesis of a fixed Regge pole, the results indicate that the data on the structure function are consistent with an asymptotic behaviour given by leading Reggeon contributions. We also show that the minimum of the lower bound as a function of the subtraction constant $S_1^{\text{inel}}(Q^2)$ provides a reasonable estimate of this quantity, in a frame similar, but not identical to the Reggeon dominance hypothesis.

   hep-phEPJC(2021)·3 citations
7. 07*

   A Phenomenological analysis on isospin-violating decay of $X(3872)$

   Qi Wu🇨🇳 · Dian-Yong Chen🇨🇳 · Takayuki Matsuki🇯🇵

   In a molecular scenario, we investigate the isospin-breaking hidden charm decay processes of $X(3872)$, i.e., $X(3872)\to {\pi }^{+}{\pi }^{-}J/\psi$, $X(3872)\to {\pi }^{+}{\pi }^{-}{\pi }^{0}J/\psi$, and $X(3872)\to {\pi }^0{\chi }_{cJ}$. We assume that the source of the strong isospin violation comes from the different coupling strengths of $X(3872)$ to its charged components $D^{\ast +}{D}^{-}$ and neutral components $D^{\ast 0}{\bar{D}}^0$ as well as the interference between the charged meson loops and neutral meson loops. The former effect could fix our parameters by using the measurement of the ratio $\Gamma [X(3872)\to {\pi }^{+}{\pi }^{-}{\pi }^{0}J/\psi ]/\Gamma [X(3872)\to {\pi }^{+}{\pi }^{-}J/\psi ]$. With the determined parameter range, we find that the estimated ratio $\Gamma [X(3872)\to {\pi }^0{\chi }_{c1}/\Gamma [X(3872)\to {\pi }^{+}{\pi }^{-}J/\psi ]$ is well consistent with the experimental measurement from the BESIII collaboration. Moreover, the partial width ratio of ${\pi }^0{\chi }_{cJ}$ for $J=0,1,2$ is estimated to be $1.77\sim 1.65:1:1.09\sim 1.43$, which could be tested by further precise measurements of BESIII and Belle II.

   hep-phhep-exEPJC(2021)·49 citations
8. 08*

   Leptophilic fermion WIMP ~ Role of future lepton colliders

   Shun-ichi Horigome🇯🇵 · Taisuke Katayose🇯🇵 · Shigeki Matsumoto🇯🇵 · Ipsita Saha🇯🇵

   The leptophilic weakly interacting massive particle (WIMP) is realized in a minimal renormalizable model scenario where scalar mediators with lepton number establish the WIMP interaction with the standard model (SM) leptons. We perform a comprehensive analysis for such a WIMP scenario for two distinct cases with an SU(2) doublet or singlet mediator considering all the relevant theoretical, cosmological and experimental constraints at present. We show that the mono-photon search at near-future lepton collider experiments (ILC, FCC-ee, CEPC, etc.) can play a significant role to probe the yet unexplored parameter range allowed by the WIMP relic density constraint. This will complement the search prospect at the near-future hadron collider experiment (HL-LHC). Furthermore, we discuss the combined model scenario including both the doublet and singlet mediator. The combined model is capable of explaining the long-standing muon (g-2) anomaly which is an additional advantage. We demonstrate that the allowed region for anomalous muon (g-2) explanation, which has been updated very recently at Fermi National Accelerator Laboratory, can also be probed at the future colliders which will thus be a simultaneous authentication of the model scenario.

   hep-phPRD(2021)·30 citations
9. 09*

   Production of hidden-charm strange pentaquarks $P_{cs}$ from the $K^{-}p\to J/\psi \Lambda$ reaction

   Samson Clymton🇰🇷 · Hee-Jin Kim🇰🇷 · Hyun-Chul Kim🇰🇷

   We investigate the production of the hidden-charm pentaquark $P_{cs}^0(4459)$ with strangeness in the $K^{-}p\to J/\psi \Lambda$ reaction, employing two different theoretical frameworks, i.e., the effective Lagrangian method and the Regge approach. Having determined all relevant coupling constants, we are able to compute the total and differential cross sections for the $K^{-}p\to J/\psi \Lambda$ reaction. We examine the contributions of $P_{cs}$ with different sets of spin-parity quantum number assigned. The present results may give a guide for possible future experiments.

   hep-phhep-exPRD(2021)·20 citations
10. 10*

    Metastable strings and dumbbells in supersymmetric hybrid inflation

    Wilfried Buchmuller🇩🇪

    We study symmetry breaking and topological defects in a supersymmetric model with gauge group $\text{U}(2)$, which can be identified with the right-handed part $\text{SU}(2{)}_R\times \text{U}(1{)}_{B-L}$ of an extended electroweak symmetry of the Standard Model. The model has two phases of hybrid inflation terminated by tachyonic preheating where either monopoles and strings or, alternatively, dumbbells are formed. In the first case a stochastic gravitational wave background is predicted in the LIGO-Virgo band, possibly extending to the LISA frequency band and to nanohertz frequencies, which is generated by a metastable cosmic string network. In the second case no topological defects survive inflation and no stochastic gravitational wave background is produced.

    hep-phastro-ph.COhep-thJHEP(2021)·33 citations
11. 11*

    New ideas for handling of loop and angular integrals in D-dimensions in QCD

    Valery E. Lyubovitskij🇩🇪 · Fabian Wunder🇩🇪 · Alexey S. Zhevlakov🇷🇺

    We discuss new ideas for consideration of loop diagrams and angular integrals in $D$-dimensions in QCD. In case of loop diagrams, we propose the covariant formalism of expansion of tensorial loop integrals into the orthogonal basis of linear combinations of external momenta. It gives a very simple presentation for the final results and is more convenient for calculations on computer algebra systems. In case of angular integrals we demonstrate how to simplify the integration of differential cross sections over polar angles. Also we derive the recursion relations, which allow to reduce all occurring angular integrals to a short set of basic scalar integrals. All order $ϵ$-expansion is given for all angular integrals with up to two denominators based on the expansion of the basic integrals and using recursion relations. A geometric picture for partial fractioning is developed which provides a new rotational invariant algorithm to reduce the number of denominators.

    hep-phJHEP(2021)·28 citations
12. 12*

    Effective field theory interpretation of lepton magnetic and electric dipole moments

    Jason Aebischer🇺🇸 · Wouter Dekens🇺🇸 · Elizabeth E. Jenkins🇺🇸 · Aneesh V. Manohar🇺🇸 · Dipan Sengupta🇺🇸 · Peter Stoffer🇺🇸

    We perform a model-independent analysis of the magnetic and electric dipole moments of the muon and electron. We give expressions for the dipole moments in terms of operator coefficients of the low-energy effective field theory (LEFT) and the Standard Model effective field theory (SMEFT). We use one-loop renormalization group improved perturbation theory, including the one-loop matching from SMEFT onto LEFT, and one-loop lepton matrix elements of the effective-theory operators. Semileptonic four-fermion operators involving light quarks give sizable non-perturbative contributions to the dipole moments, which are included in our analysis. We find that only a very limited set of the SMEFT operators is able to generate the current deviation of the magnetic moment of the muon from its Standard Model expectation.

    hep-phhep-exJHEP(2021)·111 citations
13. 13*

    CMS measurements of EFT parameters with top quarks

    Nicolas Tonon🇩🇪

    Measurements carried out or reinterpreted within the framework of effective field theory (EFT) will constitute a key component of the LHC legacy in the quest towards physics beyond the standard model. Numerous EFT measurements were already published by the CMS Collaboration. In the top quark sector, four distinct approaches to EFT have been identified, each successfully applied in several analyses. We review the pros and cons of each approach, while illustrating them with recent analyses in which they were adopted.

    ↳ hep-exhep-ph0 citations
14. 14*

    Possibility of measurement of cosmic ray electron spectrum up to 100 TeV with two-layer water Cherenkov detector array

    A.Neronov🇫🇷 · D.Semikoz🇫🇷

    Measurements of cosmic ray electron+positron spectrum above 10 TeV with ground-based experiments is challenging because of the difficulty of rejection of hadronic extensive air shower background. We study the efficiency of rejection of the hadronic background with water Cherenkov detector array supplemented by muon detection layer. We show that addition of a continuous muon detection layer to the experimental setup allows to achieve a ~ 1e-5 rejection factor for hadronic background at 10 TeV and enables measurement of electron spectrum in 10-100 TeV energy range. We show that measurements of electron spectrum in this energy range do not require a high-altitude experiment and can be done with a sea-level detector.

    ↳ astro-ph.HEhep-ph2 citations
15. 15*

    Constraints on power law cosmology from cosmic chronometer, standard ruler, and standard candle data

    Joseph Ryan🇺🇸

    In this paper I investigate how well simple power law expansion fits observational data in comparison to the standard $\Lambda$CDM model. I analyze a data set consisting of cosmic chronometer, standard ruler, and standard candle measurements, finding that the $\Lambda$CDM model provides a better fit to most combinations of these data than the power law ansatz.

    ↳ astro-ph.COgr-qchep-phhep-thJCAP(2021)·10 citations
16. 16*

    Exploring the QCD phase diagram with fluctuations

    Volker Koch🇺🇸 · Volodymyr Vovchenko🇺🇸

    We report on recent progress concerning theoretical description of event-by-event fluctuations in heavy-ion collisions. Specifically we discuss a new Cooper-Frye particlization routine -- the subensemble sampler -- which is designed to incorporate effects of global conservation laws, thermal smearing and resonance decays on fluctuation measurements in various rapidity acceptances. First applications of the method to heavy-ion collisions at the LHC energies are presented and further necessary steps to analyze fluctuations from RHIC beam energy scan are outlined.

    ↳ nucl-thhep-phActa Phys.Polon.B(2021)·1 citation
17. 17*

    Axion search with quantum nondemolition detection of magnons

    Tomonori Ikeda🇯🇵 · Asuka Ito🇹🇼 · Kentaro Miuchi🇯🇵 · Jiro Soda🇯🇵 · Hisaya Kurashige🇯🇵 · Yutaka Shikano🇯🇵

    The axion provides a solution for the strong CP problem and is one of the leading candidates for dark matter. This paper proposes an axion detection scheme based on quantum nondemolition detection of magnon, i.e., quanta of collective spin excitations in solid, which is expected to be excited by the axion-electron interaction predicted by the Dine-Fischer-Srednicki-Zhitnitsky (DFSZ) model. The prototype detector is composed of a ferrimagnetic sphere as an electronic spin target and a superconducting qubit. Both of these are embedded inside a microwave cavity, which leads to a coherent effective interaction between the uniform magnetostatic mode in the ferrimagnetic crystal and the qubit. An upper limit for the coupling constant between an axion and an electron is obtained as $g_{aee}<2.6\times 10^{-6}$ at the 95% confidence level for the axion mass of $33.117$$\mu$eV $<m_a<33.130$$\mu$eV.

    ↳ hep-exastro-ph.COhep-phphysics.ins-det+1PRD(2022)·34 citations
18. 18*

    Peeking into the $\theta$ vacuum

    Ryuichiro Kitano🇯🇵 · Ryutaro Matsudo🇯🇵 · Norikazu Yamada🇯🇵 · Masahito Yamazaki🇯🇵

    We propose a subvolume method to study the $\theta$ dependence of the free energy density of the four-dimensional SU($N$) Yang-Mills theory on the lattice. As an attempt, the method is first applied to SU(2) Yang-Mills theory at $T=1.2T_c$ to understand the systematics of the method. We then proceed to the calculation of the vacuum energy density and obtain the $\theta$ dependence qualitatively different from the high temperature case. The numerical results combined with the theoretical requirements provide the evidence for the spontaneous CP violation at $\theta =\pi$, which is in accordance with the large $N$ prediction and indicates that the similarity between 4d SU($N$) and 2d CP${}^{N-1}$ theories does not hold for $N$=2.

    ↳ hep-lathep-phhep-thPLB(2021)·25 citations
19. 19*

    Massive $\Delta$-resonance admixed hypernuclear stars with anti-kaon condensations

    Vivek Baruah Thapa🇮🇳 · Monika Sinha🇮🇳 · Jia Jie Li🇨🇳 · Armen Sedrakian🇩🇪

    In this work, we study the effect of (anti)kaon condensation on the properties of compact stars that develop hypernuclear cores with and without an admixture of $\Delta$-resonances. We work within the covariant density functional theory with the parameters adjusted to $K$-atomic and kaon-nucleon scattering data in the kaonic sector. The density-dependent parameters in the hyperonic sector are adjusted to the data on $\Lambda$ and ${\Xi }^{-}$ hypernuclei data. The $\Delta$-resonance couplings are tuned to the data obtained from their scattering off nuclei and heavy-ion collision experiments. We find that (anti)kaon condensate leads to a softening of the equation of state and lower maximum masses of compact stars than in the absence of the condensate. Both the $K^{-}$ and ${\bar{K}}^0$-condensations occur through a second-order phase transition, which implies no mixed-phase formation. For large values of (anti)kaon and $\Delta$-resonance potentials in symmetric nuclear matter, we observe that condensation leads to an extinction of ${\Xi }^{-,0}$ hyperons. We also investigate the influence of inclusion of additional hidden-strangeness ${\sigma }^{\ast }$ meson in the functional and find that it leads to a substantial softening of the equation of state and delay in the onset of (anti)kaons.

    ↳ astro-ph.HEhep-phPRD(2021)·58 citations
20. 20*

    Constraining Light Dark Photons from GW190517 and GW190426_152155

    Diptimoy Ghosh🇮🇳 · Divya Sachdeva🇮🇳

    Ultralight dark photons predicted in several Standard Model extensions can trigger the superradiant instability around rotating black holes if their Compton wavelength is comparable to the Blackhole radius. Consequently, the angular momentum of the black hole is reduced to a value which depends upon the mass and spin of the black hole as well as the mass of the dark photon. We use the mass and spin measurements of the primary black holes in two recently observed binary black hole systems: GW190517 and GW190426_152155 to constrain dark photon mass in the ranges $1.7\times 10^{-14}\mathrm{eV}<m_{A^{\prime }}<7.6\times 10^{-13}\mathrm{eV}$ and $1.3\times 10^{-13}\mathrm{eV}<m_{A^{\prime }}<4.2\times 10^{-12}\mathrm{eV}$ respectively, assuming a timescale of a few million years from the time of formation of the binary black hole system to the time of their merger. We also discuss an interesting X-ray binary system, MAXI J1820_070, albeit with a relatively small value of the spin parameter.

    ↳ astro-ph.HEastro-ph.COgr-qchep-phPRD(2021)·16 citations
21. 21*

    Gravitational wave cosmology I: high frequency approximation

    Jared Fier🇺🇸 · Xiongjun Fang🇨🇳 · Bowen Li🇺🇸 · Shinji Mukohyama🇯🇵 · Anzhong Wang🇺🇸 · Tao Zhu🇨🇳

    In this paper, we systematically study gravitational waves (GWs) produced by remote compact astrophysical sources. To describe such GWs properly, we introduce three scales, $\lambda ,L_c$ and $L$, denoting, respectively, the typical wavelength of GWs, the scale of the cosmological perturbations, and the size of the observable universe. For GWs to be detected by the current and foreseeable detectors, the condition $\lambda \ll L_c\ll L$ holds, and such GWs can be well approximated as high-frequency GWs. In order for the backreaction of the GWs to the background to be negligible, we must assume that $\left|h_{\mu \nu }\right|\ll 1$, in addition to the condition $ϵ\ll 1$, which are also the conditions for the linearized Einstein field equations for $h_{\mu \nu }$ to be valid, where $g_{\mu \nu }={\gamma }_{\mu \nu }+ϵh_{\mu \nu }$, and ${\gamma }_{\mu \nu }$ denotes the background. To simplify the field equations, we show that the spatial, traceless, and Lorentz gauge conditions can be imposed simultaneously, even when the background is not vacuum, as long as the high-frequency GW approximation is valid. However, to develop the formulas that can be applicable to as many cases as possible, we first write down explicitly the linearized Einstein field equations by imposing only the spatial gauge. Applying the general formulas together with the geometrical optics approximation to such GWs, we find that they still move along null geodesics and its polarization bi-vector is parallel-transported, even when both the cosmological scalar and tensor perturbations are present. In addition, we also calculate the gravitational integrated Sachs-Wolfe effects, whereby the dependences of the amplitude, phase and luminosity distance of the GWs on these two kinds of perturbations are read out explicitly.

    ↳ astro-ph.COastro-ph.HEgr-qchep-ph+1PRD(2021)·17 citations
22. 22*

    Collider constraints on axion-like particles

    David d'Enterria🇨🇭

    The current status and future prospects of searches for axion-like particles (ALPs) at colliders, mostly focused on the CERN LHC, are summarized. Constraints on ALPs with masses above a few GeV that couple to photons, as well as to Z or Higgs bosons, have been set at the LHC through searches for new $a\to \gamma \gamma$ resonances in di-, tri-, and four-photon final states. Inclusive and exclusive diphotons in proton-proton and lead-lead collisions, pp, PbPb $\to a\to \gamma \gamma (+X)$, as well as exotic Z and Higgs boson decays, pp $\to \mathrm{Z},\mathrm{H}\to a\gamma \to 3\gamma$ and pp $\to \mathrm{H}\to aa\to 4\gamma$, have been analyzed. Exclusive searches in PbPb collisions provide the best exclusion limits for ALP masses $m_a\approx 5-$100 GeV, whereas the other channels are the most competitive ones over $m_a\approx 100$ GeV$-$2.6 TeV. Integrated ALP production cross sections up to $\sim$100 nb are excluded at 95% confidence level, corresponding to constraints on axion-photon couplings down to $g_{a\gamma }\approx$ 0.05 TeV${}^{-1}$, over broad mass ranges. Factors of 10$-$100 improvements in these limits are expected at the LHC approaching $g_{a\gamma }\approx 10^{-3}$ TeV${}^{-1}$ over $m_a\approx 1$ GeV$-$5 TeV in the next decade.

    ↳ hep-exhep-phnucl-exnucl-th87 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.