INSPIRE - Topcites 2017 Edition Review

In the 2016 INSPIRE Topcites blog post, we suggested that it would be interesting to see what happened in 2017 following the discovery of gravitational waves. The original February 2016 LIGO/Virgo discovery [2] was joined by the observation of a second black hole merger in June 2016 [13] that makes its first appearance in the Top Forty. Even more striking this year was the discovery of a merger of two neutron stars. Unlike the case of black holes, neutron star mergers explode visible matter outside the event horizon of the final black hole, producing dramatic signatures in visible, X-ray, and gamma-ray radiation. This discovery was reported in one paper for the gravitational wave signal and another for the multi-messenger signal.

The implications of these observations are mainly for astrophysics rather than particle physics, but they are nevertheless spectacular - for example, providing evidence for neutron star mergers as the origin of heavy elements beyond iron in the galaxy. But the event also has implications for theories of gravity, since the simultaneous observation of gravity and electromagnetic waves demonstrates that these signals have the same speed to better than 1 part in 1015, excluding many alternatives to general relativity as the theory of gravity at very large scales (see, for example, these papers).

The discovery papers appeared only in October, and so did not yet accumulate the 300 citations needed for a spot on this year's Top Forty list. Look for these papers to appear prominently in 2018.

The top position in this year's list is held by the 2015 paper on cosmological parameters by the Planck Collaboration [1]. Two related papers from Planck [16,17] and the papers on the discovery of dark energy [18,21] also appear on the Top Forty list. This reflects the continuing importance to particle physics of information from cosmology, which informs our understanding (or lack thereof) of many of the major open issues of the field: dark matter, neutrino mass, quantum gravity, grand unification and new fields at extremely high energy (through models of cosmic inflation), and the nature of the Higgs boson. The Planck paper also shares 150 citations with the gravity wave observation paper [2]. Foundational papers on quantum gravity and inflation by Hawking [20], Guth [24], Starobinsky [25], and Bekenstein [39] also seem to have received a boost from the LIGO discovery. In particular, Bekenstein's paper makes its first appearance on the list this year.

The upper bound on the spin-independent dark matter cross section from the LUX Collaboration appears at [23]. The search for direct detection of dark matter continues apace, with new results from XENON and PandaX that appeared too late to accumulate sufficient citations for this year's list.

Just below the astrophysics and cosmology papers, we find the ATLAS and CMS papers on the discovery of the Higgs boson [3,4]. The ATLAS/CMS combined measurements of the Higgs boson couplings and mass also appear as [27,37]. Though these papers are from past measurements, the experimental study of the Higgs boson continues to pass new milestones. This past year, the discovery of the Higgs boson decay to b quarks completed the observation of the major Higgs boson decay modes. Papers on the ATLAS and CMS detectors appear at [11,12].

The continuing quest for an understanding of neutrino mass is represented on this year's list by the appearance of papers by Minkowski [30] and Mohapatra and Senjanovic's [34] on the seesaw mechanism for obtaining small neutrino masses. As in past years, we apologize that the earlier papers that introduced this mechanism by Yanagida, and Gell-Mann, Ramond, and Slansky do not appear, for reasons discussed in the Neutrino section of the 2003 Topcites Review. In 2003, Minkowski's paper -- truly the first one on this subject -- had only 16 citations; now this paper is properly recognized with almost 3,000 citations.

We are pleased to see that many of the positions in the Top Forty are held by papers that document impressive tools provided by our community to assist the analysis of experiments. These include papers on the GEANT4 simulation framework [7], the event generator PYTHIA [8,10,26], advanced methods for the study of hadronic jets [9,15], and parton distribution functions [22,33]. Also included are papers explaining remarkable codes that automate the calculation of cross sections to next-to-leading order [5,28,38], allowing everyone to explore the consequences of predictions with high theoretical precision. These tools require considerable effort and invention, and their creators deserve much credit. Please keep citing them! The list also includes two papers on statistical methods for collider physics [29,36]. These are useful papers, but we cannot hide our disappointment; the subject of these papers is how to present negative results of new physics searches.

The remaining papers are classic theoretical works on the AdS/CFT correspondence [6,14,19,32], the gauge hierarchy problem [31], and the strong CP problem [35].

Heath O'Connell and Michael Peskin

INSPIRE Topcites homepage