John Ellis on the Symbiosis Between Particle Physics & Astrophysics

Special Topic of Supersymmetry Interview, January 2012

John Ellis

John Ellis with Dimitri Nanopoulos (left) and Keith Olive (right). © CERN.

Our Special Topics analysis of supersymmetry research over the past decade shows that the work of Professor John Ellis ranks at #1 by total citations and by total papers, based on 134 papers cited a total of 4,632 times. Two of these papers appear on the top 20 papers lists over the past decade and over the past two years.

His work also appears in Essential Science IndicatorsSM from Thomson Reuters, where he ranks among the top 1% of researchers in Physics, with 164 papers cited a total of 4,594 times between January 1, 2001 and August 31, 2011.

Ellis is the James Clerk Maxwell Professor of Theoretical Physics at King's College London. He is also a Guest Professor in the Theory Division at CERN in Geneva, Switzerland, where he serves on the Steering Committee for the Compact Linear Collider (CLIC), and was a founding member of the committees selecting experiments for the Large Electron-Positron (LEP) Collider and the Large Hadron Collider (LHC).

Below, he talks with about his highly cited work as it relates to supersymmetry.

SW: Would you tell us a bit about your educational background and research experiences?

I went to school in London in the UK, and then studied applied mathematics and theoretical physics at Cambridge University as an undergraduate (1964 to 1967), continuing there to do my Ph.D., which I obtained in 1971.

SW: What first drew your interest to the research area of supersymmetry?

I first got interested in the mid-1970s, stimulated by the early papers of Wess, Zumino, and others formulating supersymmetric field theories. But it was rather academic curiosity until various people (Maiani, Witten, etc.) realized around 1980 that supersymmetric particles weighing about a TeV could help stabilize the electroweak mass scale by making quantum corrections naturally small.

Then in 1984, together with Hagelin, Nanopoulos, Olive, and Srednicki, we realized that the lightest supersymmetric particle would be a very natural candidate for cold dark matter and calculated its density in some detail (this paper now has over 1,000 citations in the SPIRES database; Ellis J, et al., "Supersymmetric relics from the Big Bang," Nuclear Physics B 238[2]: 453-76, 1984).

John Ellis
John Ellis with a large number of his collaborators. © CERN.

In 1990-91, in two papers together with Kelley and Nanopoulos ("Probing the desert using gauge coupling unification," Physics Letters B 260[1-2]: 131-7, 9 May 1991 and "Precision LEP data, supersymmetric guts and string unification," Physics Letters B 249[3-4]: 441-8, 25 October 1990) we also showed that supersymmetry would help unify the couplings of the Standard Model interactions, which had recently been measured accurately at LEP (795 and 429 citations, respectively).

Around that time, together with Ridolfi and Zwirner, we also calculated the mass of the lightest supersymmetric Higgs boson (over 1,000 citations; "Radiative corrections to the masses of supersymmetric Higgs bosons," Physics Letters B 257[1-2]: 83-91, 21 March 1991), getting a result that is very consistent with the indications from indirect data and the very recent direct evidence from searches at the LHC.

SW: Your most-cited paper in our analysis is the July 2003 Physics Letters B paper, "Supersymmetric dark matter in light of WMAP," (Ellis J, et al., 565[1-4]: 176-82, 17 July 2003). Could you talk a little bit about this paper and why it has been so influential?

We were among the first to realize that the new era of precision cosmology ushered in by the WMAP data would also constrain quite accurately models of physics beyond the Standard Model. Specifically, WMAP permitted a determination of the dark matter density that imposed important constraints on supersymmetric model parameters. This occurred at a time when physicists were looking forward to the searches for supersymmetry at the LHC and in astroparticle physics, so it was "the right paper in the right place at the right time."

SW: One of the aspects of your work is "particle astrophysics." Would you tell us about this, and some of the key papers you have published in this area (on our list or not)?

It has been realized since the 1970s that many fundamental issues in cosmology (origin of matter, nature of dark matter, etc.) can be resolved only by particle physics. Conversely, high-energy particles from astrophysical sources may cast light on fundamental physics. Hence a tight symbiotic relationship between particle physics and astrophysics has developed.

"During the past decade physicists were looking forward to data from the LHC, in particular concerning the Higgs boson and supersymmetry, in the expectation that LHC experiments would tell us finally whether these hypothesized particles exist or not."

Nowadays, I almost do not notice when including some astrophysical constraint on my particle model, or calculating some cosmological property using particle physics. Particle physics, high-energy astrophysics, and cosmology have merged.

In addition to the 2003 paper above and the 1984 dark matter paper mentioned earlier, I would mention a 1979 paper with Gaillard and Nanopoulos on baryogenesis (276 citations; "Baryon number generation in grand unified theories," Physics Letters B 80[4-5]: 360-4, 1979), several papers in the 1990s with Olive and others on the dark matter relic density and LEP constraints on supersymmetry, and recent papers on your list with Olive, Spanos, and others on dark matter detection.

SW: Earlier this year, you coauthored a paper that is already attracting citation attention: "Implications of initial LHC searches for supersymmetry," (European Physical Journal C 71[5]: art. no. 1634, May 2011). Please tell us about this paper.

The LHC is exploring for the first time the TeV energy range, which is where many of us expect supersymmetry to appear. The initial LHC results directly impact these expectations, and this paper discusses the impact. This paper is actually one of series that started in 2008, and it has been followed by a couple of more recent papers in 2011. This work is done with a group of a dozen or so people, roughly half theorists and half experimentalists, and makes a probabilistic global analysis of all experimental data relevant to supersymmetry, the most recent also discussing possible implications of the possible observation of the Higgs boson at the LHC.

SW: How have ideas on supersymmetry changed in the past decade? What are the primary challenges that remain to be met in the next?

During the past decade physicists were looking forward to data from the LHC, in particular concerning the Higgs boson and supersymmetry, in the expectation that LHC experiments would tell us finally whether these hypothesized particles exist or not. Before the LHC started, there was hope that the LHC might find supersymmetry in its initial runs. This has not happened so far, as discussed in the above papers, and there is some disappointment in the air among theorists.

However, the LHC is only at the beginning of its journey, and it will be some years before we know the answer. The primary challenge for experimentalists is to make their searches as sensitive as possible, and the primary challenge for theorists is to imagine all the possible signatures of supersymmetry that they could or should look for.End

John Ellis, Ph.D., FRS
Physics Department
King's College London
London, UK
Theory Division
Geneva, Switzerland


Ellis J., et al., “Supersymmetric dark matter in light of WMAP,” Phys. Lett. B. 565(1-4): 176-82, 17 July 2003 with 235 cites. Source: Essential Science Indicators from Clarivate Analytics.



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