Tue·Sep 27, 2005Tuesday·September 27, 2005

1. 01*

   Chiral limit of 2-color QCD at strong couplings

   Shailesh Chandrasekharan🇺🇸 · Fu-Jiun Jiang (Duke University)🇺🇸

   We study two-color lattice QCD with massless staggered fermions in the strong coupling limit using a new and efficient cluster algorithm. We focus on the phase diagram of the model as a function of temperature $T$ and baryon chemical potential $\mu$ by working on $L_t\times L^d$ lattices in both $d=2,3$. In $d=3$ we find that at $\mu =0$ the ground state of the system breaks the global U(2) symmetry present in the model to U(1), while the finite temperature phase transition (with $L_t=4$) which restores the symmetry is a weak first order transition. In $d=2$ we find evidence for a novel phase transition similar to the Berezinky-Kosterlitz-Thouless phenomena. On the other hand the quantum (T=0) phase transition to a symmetric phase as a function of $\mu$ is second order in both $d=2,3$ and belongs to the mean field universality class.

   hep-latPoS(2006)·6 citations
2. 02*

   Chiral phase transition as an Anderson transition in the Instanton Liquid Model for QCD

   Antonio M. Garcia-Garcia🇺🇸 · James C. Osborn🇺🇸

   We study the spectrum and eigenmodes of the QCD Dirac operator in a gauge background given by an Instanton Liquid Model (ILM) at temperatures around the chiral phase transition. For two massless quark flavors we observe that at the chiral phase transition, both the low lying eigenmodes and the spectrum of the QCD Dirac operator resemble those of a disordered conductor at the Anderson transition. In particular we present results showing that the eigenvectors are multifractal and the spectral correlations are well described by critical statistics. We also find an additional temperature dependent mobility edge located in the bulk of the spectrum with properties quantitatively similar to those of a 3D disordered conductor at the Anderson transition. This feature is present in both quenched and unquenched simulations. Finally we argue that our findings are not in principle restricted to the ILM approximation and may also be found in lattice simulations.

   hep-latcond-mat.dis-nnhep-thPoS(2006)·5 citations
3. 03*

   QCD Level Density from Maximum Entropy Method

   Shinji Ejiri🇯🇵 · Tetsuo Hatsuda🇯🇵

   We propose a method to calculate the QCD level density directly from the thermodynamic quantities obtained by lattice QCD simulations with the use of the maximum entropy method (MEM). Understanding QCD thermodynamics from QCD spectral properties has its own importance. Also it has a close connection to phenomenological analyses of the lattice data as well as experimental data on the basis of hadronic resonances. Our feasibility study shows that the MEM can provide a useful tool to study QCD level density.

   hep-latPoS(2006)·4 citations
4. 04*

   Electromagnetic mass difference on the lattice

   Yusuke Namekawa🇯🇵 · Yoshio Kikukawa🇯🇵

   We calculate electromagnetic mass difference of mesons using a method proposed by Duncan {\it et al}. The RG-improved gauge action and the non-compact Abelian gauge action are employed to generate configurations. Quark propagators in the range of $m_{PS}/m_V=0.76-0.51$ are obtained with the meanfield-improved clover quark action. Chiral and continuum extrapolations are performed and the results are compared with experiments. Finite size effects are also examined. Quark masses are extracted from the measured spectrum. Our preliminary values for light quark masses are $m_u^{\overline{MS}}(\mu =2GeV)=3.03(19)$ MeV, $m_d^{\overline{MS}}(\mu =2GeV)=4.44(28)$ MeV, $m_s^{\overline{MS}}(\mu =2GeV)=99.2(52)$ MeV.

   hep-latPoS(2006)·6 citations
5. 05*

   Lattice QCD Evidence for Exotic Tetraquark Resonance

   Hideo Suganuma (Kyoto Univ.)🇯🇵 · Kyosuke Tsumura (Kyoto Univ.)🇯🇵 · Noriyoshi Ishii (Tokyo Inst. Tech.)🇯🇵 · Fumiko Okiharu (Nihon Univ.)🇯🇵

   We study the manifestly exotic tetraquark D${}_{s0}^{++}(cu\bar{s}\bar{d})$ and the scalar tetraquark $f_0(ud\bar{u}\bar{d})$ in SU(3)${}_c$ anisotropic quenched lattice QCD with the $O(a)$-improved Wilson (clover) fermion with various quark masses including the idealized SU(4)${}_f$ case. For $f_0(ud\bar{u}\bar{d})$ etc., we only consider connected diagrams at the quenched level, i.e., the tetraquark $f_0(ud\bar{u}\bar{d})$ is identical with D${}_{s0}^{++}(cu\bar{s}\bar{d})$ in the idealized SU(4)${}_f$ case. First, for comparison, we study the lowest $q\bar{q}$ scalar meson, and find that it has a large mass of about 1.37GeV after chiral extrapolation, which corresponds to $f_0(1370)$. Second, we investigate the lowest 4Q state in the spatial periodic boundary condition, and find that it is just a scattering state of two pseudoscalar mesons, as is expected. Third, to extract spatially-localized 4Q resonances, we use the Hybrid Boundary Condition (HBC) method, where anti-periodic and periodic boundary conditions are imposed on quarks ($c$,$u$) and antiquarks ($\bar{s}$,$\bar{d}$), respectively. By applying the HBC on a finite-volume lattice, the threshold of the two-meson scattering state is raised up, while the mass of a compact 4Q resonance is almost unchanged. In HBC, we find a nontrivial 4Q resonance state about 100 MeV below the two-meson threshold in some quark-mass region. Its chiral behavior largely differs from a two-meson scattering state. The scalar tetraquark $f_0(ud\bar{u}\bar{d})$ is found to have the mass of about 1.1GeV after chiral extrapolation, and seems to correspond to $f_0(980)$. Then, the manifestly exotic tetraquark D${}_{s0}^{++}(cu\bar{s}\bar{d})$ would exist around 1GeV in the idealized SU(4)${}_f$ chiral limit. Finally, MEM analysis is applied to obtain the spectral function of the 4Q system.

   hep-latPoS(2006)·26 citations
6. 06*

   Critical temperature in QCD with two flavors of dynamical quarks

   V.G. Bornyakov🇷🇺 · M.N. Chernodub🇷🇺 · Y. Mori🇯🇵 · S.M. Morozov🇷🇺 · Y. Nakamura🇩🇪 · M.I. Polikarpov🇷🇺 · G. Schierholz🇩🇪 · A.A. Slavnov🇷🇺 · H. Stueben · T. Suzuki🇯🇵

   We present results obtained in QCD with two flavors of non-perturbatively improved Wilson fermions at finite temperature on $16^3\times 8$ and $24^3\times 10$ lattices. We determine the transition temperature in the range of quark masses $0.6<m_{\pi }/m_{\rho }<0.8$ at lattice spacing a$\approx$0.1 fm and extrapolate the transition temperature to the continuum and to the chiral limits. We also discuss the order of phase transition.

   hep-latPoS(2006)·22 citations
7. 07*

   Neutron electric dipole moment on the lattice

   Eigo Shintani🇯🇵 · S. Aoki🇯🇵 · N. Ishizuka🇯🇵 · K. Kanaya🇯🇵 · Y. Kikukawa🇯🇵 · Y. Kuramashi🇯🇵 · M. Okawa🇯🇵 · A. Ukawa🇯🇵 · T. Yoshié🇯🇵

   We carry out a feasibility study toward a lattice QCD calculation of the neutron electric dipole moment (NEDM) in the presence of the $\theta$ term using two different approaches. In the first method, we calculate the CP-odd electromagnetic form factor $F_3$, which becomes the NEDM in the zero momentum transfer limit. At the first order in $\theta$, we derive a formula connecting the lattice three-point function to the CP-odd electromagnetic form factor. In the second method we directly extract the NEDM from the energy difference between spin-up and spin-down neutron states in the presence of a constant electric field, without expanding a small but non-zero $\theta$. We test both approaches numerically, employing the domain-wall quark action with the RG improved gauge action in quenched QCD at $a^{-1}\simeq 2$ GeV on a $16^3\times 32\times 16$ lattice, and further applying the second method to the clover quark action at a similar lattice spacing and nucleon mass. We obtain good signals from both approaches. In particular the second method works well with both fermion formulations.

   hep-lathep-phnucl-thPoS(2006)·6 citations
8. 08*

   Electromagnetic properties of hadrons with two flavors of dynamical domain wall fermions

   N. Yamada (KEK, Graduate U. Adv. Studies)🇯🇵 · T. Blum (Connecticut U. & RIKEN BNL)🇺🇸 · M. Hayakawa (RIKEN)🇯🇵 · T. Izubuchi (Kanazawa U. & RIKEN BNL) (for RBC Collaboration)🇺🇸

   We present the determination of the light quark masses using electromagnetic splittings of pions and kaons. The meson masses are calculated on $SU(3)\times U(1)$ gauge configurations, where SU(3) gauge fields include sea quark effects of two degenerate flavors and the U(1) gauge fields are incorporated in non-compact form. Possible sources of systematic uncertainty are discussed.

   hep-latPoS(2006)·9 citations
9. 09*

   Density-density correlators using all-to-all propagators

   Constantia Alexandrou🇨🇾 · Petros Dimopoulos🇮🇹 · Giannis Koutsou🇨🇾 · Hartmut Neff🇬🇧

   We present a study of gauge invariant density-density correlators. Density-density correlators probe hadron wave functions and thus can be used to study hadron deformation. Their zero momentum projection requires the computation of all-to-all propagators, which are evaluated with the standard stochastic technique, the dilution method and the stochastic sequential technique. We compare the results to a previous analysis that did not employ the zero momentum projection.

   hep-latPoS(2006)·3 citations
10. 10*

    Dynamical supersymmetry breaking and phase diagram of the lattice Wess-Zumino model

    Matteo Beccaria🇮🇹 · Gian Fabrizio De Angelis🇮🇹 · Massimo Campostrini🇮🇹 · Alessandra Feo🇮🇹

    We study dynamical supersymmetry breaking and the transition point by non-perturbative lattice techniques in a class of two-dimensional N=1 Wess-Zumino model. The method is based on the calculation of rigorous lower bounds on the ground state energy density in the infinite-lattice limit. Such bounds are useful in the discussion of supersymmetry phase transition. The transition point is determined with this method and then compared with recent results based on large-scale Green Function Monte Carlo simulations with good agreement.

    hep-latPoS(2006)·1 citation
11. 11*

    A new method for computation of QCD thermodynamics: EOS, specific heat and speed of sound

    Rajiv V. Gavai🇮🇳 · Sourendu Gupta🇮🇳 · Swagato Mukherjee🇮🇳

    We propose a new variant of the operator method for the computation of the equation of state of QCD, which yields positive pressure for all temperatures and all values of temporal lattice spacings. Using this new method, we calculate the continuum limit of pressure, energy density, entropy density, specific heat, and the speed of sound, in quenched QCD, for 0.9 \le T/T_c \le 3.

    hep-latPoS(2006)·4 citations
12. 12*

    Heavy quark masses from Fermilab Fermions

    Matthew Nobes🇺🇸 · Howard Trottier🇨🇦

    Using automated perturbation theory techniques, we have computed the one-loop mass of Fermilab fermions, with an improved gluon action. We will present the results of these calculations, and the resulting predictions for the charm and bottom quark masses in the MSbar scheme. We report mc(mc) = 1:22(9) GeV and mb(mb) = 4:7(4) GeV. In addition we present results for the one-loop coeffcients of the Fermilab action.

    hep-latPoS(2006)·14 citations
13. 13*

    J/\Psi at high temperatures in anisotropic lattice QCD

    Hideaki Iida (Tokyo Inst. Tech.)🇯🇵 · Takumi Doi (RIKEN BNL)🇺🇸 · Noriyoshi Ishii (Tokyo Inst. Tech.)🇯🇵 · Hideo Suganuma (Tokyo Inst. Tech.)🇯🇵

    J/\Psi and \eta_c above the QCD critical temperature T_c are studied in anisotropic quenched lattice QCD, considering whether the c\bar c systems above T_c are compact quasi-bound states or scattering states. We adopt the standard Wilson gauge action and O(a)-improved Wilson quark action with renormalized anisotropy a_s/a_t =4 at \beta=6.10 on 16^3\times (14-26) lattices, which correspond to the spatial lattice volume V\equiv L^3\simeq(1.55{\rm fm})^3 and temperatures T\simeq(1.11-2.07)T_c. To clarify whether compact charmonia survive in the deconfinement phase, we investigate spatial boundary-condition dependence of the energy of the c\bar c systems above T_c. In fact, for low-lying c \bar c scattering states, there appears a significant energy difference \Delta E \equiv E{\rm (APBC)}-E{\rm (PBC)} between periodic and anti-periodic boundary conditions as \Delta E\simeq2\sqrt{m_c^2+3\pi^2/L^2}-2m_c (m_c: charm quark mass) on the finite-volume lattice. In contrast, for compact charmonia, there is no significant energy difference between periodic and anti-periodic boundary conditions. As a lattice QCD result, we find almost no spatial boundary-condition dependence for the energy of the c\bar c system in J/\Psi and \eta_c channels for T\simeq(1.11-2.07)T_c, which indicates that J/\Psi and \eta_c would survive as compact c\bar c quasi-bound states below 2T_c.

    hep-latPoS(2006)·22 citations
14. 14*

    Status of the APENet project

    R. Ammendola🇮🇹 · R. Petronzio🇮🇹 · D. Rossetti🇮🇹 · A. Salamon🇮🇹 · N. Tantalo🇮🇹 · P. Vicini🇮🇹

    We present the current status of APENet, our custom 3-dimensional interconnect architecture for PC clusters environment. We report some micro-benchmarks on our recent large installation as well as new developments on the software and hardware side. The low level device driver has been reworked by following a custom hardware RDMA architecture, and MPICH-VMI, an implementation of the MPI library, has been ported to APENet.

    hep-latPoS(2006)·3 citations
15. 15*

    Dynamical twisted mass fermions

    F. Farchioni🇩🇪 · P. Hofmann🇩🇪 · K. Jansen🇩🇪 · I. Montvay🇩🇪 · G. Munster🇩🇪 · M. Papinutto🇩🇪 · E. E. Scholz🇩🇪 · L. Scorzato🇩🇪 · A. Shindler🇩🇪 · N. Ukita🇩🇪 · C. Urbach🇩🇪 · U. Wenger🇩🇪 · I. Wetzorke🇩🇪

    We summarize four contributions about dynamical twisted mass fermions. The resulting report covers results for N_f=2 obtained from three different gauge actions, namely the standard Wilson plaquette gauge action, the DBW2 and the tree-level Symanzik improved gauge action. In addition, first results for N_f=2+1+1 flavours of twisted mass fermions are discussed.

    hep-latPoS(2006)·28 citations
16. 16*

    Monte-Carlo simulation of the chiral Gross-Neveu model

    Tomasz Korzec🇩🇪 · Francesco Knechtli🇩🇪 · Ulli Wolff🇩🇪 · Bjorn Leder🇩🇪

    We investigate the two flavor chiral Gross-Neveu model in the Schroedinger functional on the lattice. The procedure necessary to recover chiral symmetry in the continuum limit of this model with Wilson fermions is discussed. We introduce several useful observables and present a first demonstration of the feasibility of Monte-Carlo simulations in this model.

    hep-latPoS(2006)·6 citations
17. 17*

    Structure of the Pion from Full Lattice QCD

    D. Brömmel🇩🇪 · M. Diehl🇩🇪 · M. Göckeler🇩🇪 · Ph. Hägler🇩🇪 · R. Horsley🇬🇧 · D. Pleiter🇩🇪 · P.E.L. Rakow🇬🇧 · A. Schäfer🇩🇪 · G. Schierholz🇩🇪 · J.M. Zanotti (QCDSF/UKQCD Collaboration)🇬🇧

    Moments of generalised parton distributions can be related to off-forward matrix elements of local operators. We calculate a few of the leading twist matrix elements for the pion on the lattice. The simulations are performed using two flavours of dynamical fermions and a range of pion masses from 550 to 1090 MeV. Our lattice spacings and spatial volumes lie in the range 0.07-0.12 fm and (1.6-2.2 fm)^3, respectively. Key features of our investigation are the use of O(a) improved Wilson fermions and non-perturbative renormalisation. We present first results for the two lowest moments of the generalised parton distributions of the pion and compare the pion electromagnetic form factor F_pi to experimental data. Good agreement is found between lattice data and experiment.

    hep-latPoS(2006)·48 citations
18. 18*

    The Gluon Propagator in Lattice Landau Gauge with twisted boundary conditions

    Torsten Tok🇩🇪 · Kurt Langfeld🇩🇪 · Hugo Reinhardt🇩🇪 · Lorenz von Smekal🇦🇺

    We investigate the infrared behaviour of the gluon propagator in Landau gauge on a lattice with twisted boundary conditions. Analytic calculations using Dyson-Schwinger equations, exact renormalization group and stochastic quantization show that the gluon propagator in Landau gauge approaches zero for small momentum. On the other hand lattice calculations and calculations on a four-torus seem to give rise to a non-zero limit. One possible reason for this difference is the existence of zero-momentum fluctuation modes which potentially give a massive contribution to the gluon propagator. Our simulations show that with twisted boundary conditions these zero-momentum modes are suppressed and the gluon propagator becomes smaller than in a periodic ensemble.

    hep-latPoS(2006)·8 citations
19. 19*

    $\Delta I=3/2$ kaon weak matrix elements with non-zero total momentum

    T. Yamazaki (for the RBC Collaboration)🇺🇸

    We present preliminary results for the $\Delta I=3/2$ kaon decay matrix elements using domain wall fermions and the DBW2 gauge action at one coarse lattice spacing corresponding to $a^{-1}=1.3$ GeV. We employ an extention of the Lellouch and Lüscher formula for non-zero total momentum to extract the infinite volume, center-of-mass system decay amplitudes. We compare the result of $\mathrm{Re}{A}_2$ with previous results calculated by several methods, and experiment. We also show the I=2 $\pi \pi$ scattering phase shift.

    hep-latPoS(2006)·5 citations
20. 20*

    Dirac-Kähler fermions and exact lattice supersymmetry

    Simon Catterall🇺🇸

    We discuss a new approach to putting supersymmetric theories on the lattice. The basic idea is to start from a {\it twisted} formulation of the underlying supersymmetric theory in which the fermions are represented as grassmann valued antisymmetric tensor fields. The original supersymmetry algebra is replaced by a twisted algebra which contains a scalar nilpotent supercharge $Q$. Furthermore the action of the theory can then be written as the $Q$-variation of some function. The case of $\mathcal{N}=2$ super Yang-Mills theory in two dimensions is discussed in some detail. We then present our proposal for discretizing this theory and derive the resultant lattice action. The latter is local, free of spectrum doubling, gauge invariant and preserves the scalar supercharge invariance exactly. Some preliminary numerical results are then presented. The approach can be naturally generalized to yield a lattice action for $\mathcal{N}=4$ super Yang-Mills in four dimensions.

    hep-lathep-thPoS(2006)·31 citations
21. 21*

    Update on pi and K Physics

    MILC Collaboration: C. Bernard🇺🇸 · C. DeTar🇺🇸 · Steven Gottlieb🇺🇸 · U.M. Heller🇺🇸 · J.E. Hetrick🇺🇸 · L. Levkova🇺🇸 · F. Maresca🇺🇸 · J. Osborn🇺🇸 · D. Renner🇺🇸 · R. Sugar🇺🇸 · D. Toussaint🇺🇸

    We present an update of the MILC studies of the physics of light pseudoscalars using improved staggered fermions. New runs at lighter quark mass, as well as increased statistics for older sets, are enabling us to improve the results for decay constants in full QCD. In addition, we have analyzed quenched runs at two different lattice spacings. This makes possible a test of the applicability of staggered chiral perturbation theory in a different context.

    hep-latPoS(2006)·36 citations
22. 22*

    Bottomonia correlators and spectral functions at zero and finite temperature

    K. Petrov🇺🇸 · A. Jakovac🇭🇺 · P. Petreczky🇺🇸 · A. Velytsky🇺🇸

    We present preliminary studies of bottomonia spectral functions at zero and finite temperature using quenched anisotropic lattices. The heavy quark is treated within Fermilab approach. We find no modification of the ${\eta }_b$ and ${\rm Y}$ states up to temperatures $2.3T_c$ while our study suggest dissolution of ${\chi }_b$ state at $1.15T_c$.

    hep-latPoS(2006)·15 citations
23. 23*

    The volume dependence of spectral weights and the pentaquark state

    Constantia Alexandrou (Univ.of Cyprus)🇨🇾 · Antonios Tsapalis (IASA, Univ. of Athens)🇬🇷

    Before studying the pentaquark system we examine the spectral weights of the two lowest scattering states in the two-pion system in the isospin I=2 channel on lattices of size $16^3\times 32$, $24^3\times 32$ and $32^3\times 64$ at $\beta =6.0$ in the quenched theory. We find that the spectral weights scale with the volume for large time separations. Therefore very accurate data are necessary in order that the spectral weights determined on different volumes yield a ratio that is precise enough to distinguish a scattering state from a single particle state. The pentaquark system is studied on the same lattices and scaling of the spectral weights of the low lying state is investigated. The accuracy of the results obtained for the scaling of spectral weights do not allow us to exclude a pentaquark resonance.

    hep-lathep-exhep-phPoS(2006)·7 citations
24. 24*

    A study of the N to Delta transition form factors in full QCD

    Constantia Alexandrou🇨🇾 · Robert Edwards🇺🇸 · Giannis Koutsou🇨🇾 · Theodoros Leontiou🇨🇾 · Hartmut Neff🇬🇧 · John W. Negele🇺🇸 · Wolfram Schroers🇩🇪 · Antonios Tsapalis🇬🇷

    The N to Delta transition form factors GM1, GE2 and GC2 are evaluated using dynamical MILC configurations and valence domain wall fermions at three values of quark mass corresponding to pion mass 606 MeV, 502 MeV and 364 MeV on lattices of spatial size $20^3$ and $28^3$. The unquenched results are compared to those obtained at similar pion mass in the quenched theory.

    hep-lathep-phnucl-exnucl-thPoS(2006)·12 citations
25. 25*

    Fermionic observables in Numerical Stochastic Perturbation Theory

    V. Miccio🇮🇹 · F. Di Renzo🇮🇹 · A. Mantovi🇮🇹 · C. Torrero🇮🇹 · L. Scorzato🇩🇪

    We present technical details of fermionic observables computations in NSPT. In particular we discuss the construction of composite operators starting from the inverse Dirac operator building block, the subtraction of UV divergences and the treatment of irrelevant contributions in extracting the continuum limit.

    hep-latPoS(2006)·0 citations
26. 26*

    Light hadron spectrum and quark masses in 2+1 flavor QCD

    CP-PACS · JLQCD Collaborations: T. Ishikawa · S. Aoki · O. Bär · M. Fukugita · S. Hashimoto · K.-I. Ishikawa · N. Ishizuka · Y. Iwasaki · K. Kanaya · T. Kaneko · Y. Kuramashi and 5 other authors

    CP-PACS and JLQCD collaborations are carrying out a joint project of the 2+1 flavor full QCD simulation. Gauge configurations are generated for the non-perturbatively $O(a)$-improved Wilson quark action and the Iwasaki gauge action using PHMC algorithm at three lattice spacings, $a\sim 0.076$, 0.010 and 0.122 fm, with a fixed physical volume $(2.0fm{)}^3$. We present analysis for the light meson spectrum and quark masses in the continuum limit, which are determined using data obtained from the simulations at the two coarser lattices. Our simulations reproduce experimental values of meson masses. The ud and strange quark masses turn out to be $m_{ud}^{\overline{MS}}(\mu =2GeV)=3.34(23)MeV$ and $m_s^{\overline{MS}}(\mu =2GeV)=86.7(5.9)MeV$. We also show preliminary results at our finest lattice spacing for which simulations are still being continued.

    hep-latPoS(2006)·17 citations
27. 27*

    The canonical approach to Finite Density QCD

    Slavo Kratochvila (Zurich, ETH)🇨🇭 · Philippe de Forcrand (Zurich, ETH & CERN)🇨🇭

    We present a canonical approach to study properties of QCD at finite baryon density rho, and apply it to the determination of the phase diagram of four-flavour QCD. For a pion mass of about 350 MeV, the first-order transition between the hadronic and the plasma phase gives rise to a co-existence region in the T-rho plane, which we study in detail. We obtain accurate results for systems containing up to 30 baryons and quark chemical potentials mu up to 2T. Our T-mu phase diagram agrees with the literature when mu/T < 1. At larger chemical potential, we observe a ``bending down'' of the phase boundary. We characterise the two phases with simple models: the hadron resonance gas in the hadronic phase, the free massless quark gas in the plasma phase.

    hep-latPoS(2006)·106 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.