# INSPIRE - Topcites 2019 Edition Review

It is a given that the Particle Data Group's Review of Particle Properties [0] resides in a class all of its own in terms of citations. In 2019, the various editions of the Review of Particle Properties attracted 4,615 citations, almost four times the number of the next most highly cited article. In the Topcite lists, the RPP is assigned the rank of 0. Among the citations to the RPP from eprints, over 80% come from the hep-ph and hep-ex categories, and interestingly, a further 5% from astro-ph.

With the increasing synergy between particle physics and cosmology, knowledge of the cosmological parameters has gained increasing importance to the papers indexed by INSPIRE. These parameters are relevant to a diverse array of topics at the heart of current research in particle physics, including dark energy, dark matter, neutrino masses, models of cosmic inflation, and other issues of physics at energies near the Planck scale. The most used fit to cosmological parameters is that of the Planck Collaboration. The 2018 edition of the Planck parameters has appeared for the first time on the 2019 Topcite list and immediately took the number [1] position. This is actually the first time that a new paper has appeared at the top position since Maldacena's revolutionary paper on the AdS/CFT correspondence [3] did this in 1998. The wide-ranging array of uses of this parameter set is reflected in the citation breakdown by arXiv category: 55% from astro-ph, 27% from hep-ph and 13% from gr-qc. At number [2] we find Planck's 2015 fit to cosmological parameters, which held the top spot last year. Planck's final entry is its 2018 update to the results concerning constraints on inflation [23], replacing the 2015 version in the Top Forty.

It is worth noting that Maldacena's paper has remained on the annual topcites list in every year since 1998. This year it appears at number [3], with 1,105 citations.

We should remark that all is not well in the set of inputs to cosmological parameters. There appears to be an increasingly significant discrepancy between the value of the Hubble constant measured in today's universe from Cepheid variable stars, supernovae, and strong gravitational lenses and the value expected by applying standard $\Lambda$CDM cosmology to early-universe measurements of the cosmic microwave background and baryon acoustic oscillations. In each domain, there are multiple consistent observations, although the error bars assigned to each are still being debated. A recent review of this subject by Verde, Treu, and Riess can be found in [a].

We noted last year that gravitational-wave astronomy had arrived as a major topic in the topcites. This year, with eight papers [5,6,27,30,31,32,34,35] in the Top Forty (three of them new to the list), gravitational waves appear to be here to stay. This group of papers includes the October 2017 paper multi-messenger paper on a neutron star-neutron star coalescence [32] that was named "2017 breakthrough of the year" by Physics World. In addition to the implications of these observations for fundamental tests of gravitation and the physics of compact astrophysical objects, it is possible that the study of gravitational waves can shed light on cosmology, including the Hubble tension problem discussed in the previous paragraph. A first measurement of the Hubble constant from a gravitational "standard siren," with well-understood systematics but low statistics (1 observation) was presented in [b].

There is one more new paper on the Top Forty, the Xenon Collaboration's 2018 limit on the dark matter direct detection cross section [26]. This supersedes the 2017 Xenon first search result which appeared in last year's list. Xenon finds no signal above background and further reduces the parameter space for WIMP models. The interest in axions as dark matter candidates propelled Peccei and Quinn's 1977 Phys.Rev.Lett. [25] to a new milestone; it passed 5,000 citations in 2019.

The Top Forty contains ten papers devoted to software tools used to analyze LHC data, including papers on the event generators GEANT4 [4], MadGraph5_aMC@NLO [7], and PYTHIA [10,12,18], the event analysis algorithm for anti-$k_T$ jet clustering algorithm [11] and the software package FastJet [16], the parton distribution set NNPDF [28] and the fast detector simulation program DELPHES 3 [39]. This group also includes an especially instructive paper by Cowan, Cranmer, Gross, and Vitells on statistical methods for setting limits on new physics [33]. When it comes to giving credit for software, we may be at the beginning of an evolutionary branch point. The currently favored model, publishing a user manual in a prestigious journal and asking anyone using using the software to cite though journal article, has been in place for many decades. The HEP Software Foundation [c] notes the recommendation of FORCE11 Software Citation Working Group [d] to broaden the concept of ''publisher'' to include both traditional publishers that publish text and/or software papers as well as archives such as Zenodo that directly publish software. We have begun to see citations to software using Zenodo-minted DOIs, though so far this seems more common in the astronomy/astrophysics community.

The remaining papers on the topcites list have been described in previous editions of the report. These include additional papers on the AdS/CFT correspondence [14,21,29], the discovery of the Higgs boson [8,9] and the detailed descriptions of the ATLAS and CMS detectors [13,15], the discovery of dark energy [17,20], and foundational papers on black holes [19,37], inflationary cosmology [22,24] and neutrino masses [36,38].

Heath O'Connell and Michael Peskin
March 2020

### References

 [a] Tensions between the Early and the Late Universe L. Verde (ICREA, Barcelona & ICC, Barcelona U.), T. Treu (UCLA, Los Angeles (main)), A.G. Riess (Johns Hopkins U. (main) & Space Telescope Science Institute). Jul 24, 2019. 10 pp. Published in Nature Astronomy 2019 DOI: 10.1038/s41550-019-0902-0 e-Print: arXiv:1907.10625 [astro-ph.CO] | PDF References | BibTeX | LaTeX(US) | LaTeX(EU) | Harvmac | EndNote ADS Abstract Service [b] First measurement of the Hubble constant from a dark standard siren using the Dark Energy Survey galaxies and the LIGO/Virgo binary-black-hole merger GW170814 DES and LIGO Scientific and Virgo Collaborations (M. Soares-Santos (Brandeis U.) et al.). Jan 6, 2019. 19 pp. Published in Astrophys.J. 876 (2019) no.1, L7 FERMILAB-PUB-18-629-AE DOI: 10.3847/2041-8213/ab14f1 e-Print: arXiv:1901.01540 [astro-ph.CO] | PDF [c] HEP Software Foundation Community White Paper Working Group - Software Development, Deployment and Validation Benjamin Couturier (CERN) et al.. Dec 21, 2017. 25 pp. HSF-CWP-2017-13 e-Print: arXiv:1712.07959 [physics.comp-ph] | PDF References | BibTeX | LaTeX(US) | LaTeX(EU) | Harvmac | EndNote CERN Document Server; ADS Abstract Service [d] Software citation principles Smith AM, Katz DS, Niemeyer KE, FORCE11 Software Citation Working Group. 2016. PeerJ Computer Science 2:e86 DOI: 10.7717/peerj-cs.86