Memorial Volume on Abdus Salam's 90th Birthday

The following sections are included:

• Preface
• Contents

The death of Abdus Salam in 1996 was a great loss not only to his family and the scientific community; it was a loss to all mankind. For he was not only one of the finest physicists of the twentieth century, having unified two of the four fundamental forces of nature, but he dedicated his life to the betterment of science and education in the developing world. So although he won the Nobel Prize for physics, a Nobel Peace Prize would have been equally appropriate…

Having significantly interacted over 17 years with Abdus Salam, as an undergraduate, postgraduate, postdoc, and eventually as an academic colleague, I will try to paint a personal picture of Salam which may convey something about the man, his greatness and his humanity…

Local events are characterized by “where”, “when” and “what”. Just as (bosonic) spacetime forms the backdrop for location and time, (fermionic) property space can serve as the backdrop for the attributes of a system. With such a scenario I shall describe a scheme that is capable of unifying gravitation and the other forces of nature. The generalized metric contains the curvature of spacetime and property separately, with the gauge fields linking the bosonic and fermionic arenas. The super-Ricci scalar can then automatically yield the spacetime Lagrangian of gravitation and the Standard Model (plus a cosmological constant) upon integration over property coordinates.

By way of paying tribute to Abdus Salam, I first recall the ideas of higher unification which the two of us introduced in 1972–73 to remove certain shortcomings in the status of particle physics prevailing then, and then present their current role in theory as well as experiments. These attempts initiated the idea of grand unification and provided the core symmetry-structure G(2, 2, 4) = SU(2)_L × SU(2)_R × SU(4)-color towards such a unification. Embodied with quark-lepton unification and left-right symmetry, the symmetry G(2, 2, 4) is uniquely chosen as being the minimal one that permits members of a family to belong to a single multiplet. The minimal extension of G(2, 2, 4) to a simple group is given by the attractive SO(10)-symmetry that was suggested a year later. The new concepts, and the many advantages introduced by this core symmetry (which are, of course, retained by SO(10) as well) are noted. These include explanations of the observed: (i) (rather weird) electroweak and color quantum numbers of the members of a family; (ii) quantization of electric charge; (iii) electron-proton charge-ratio being −1; (iv) the co-existence of quarks and leptons; (v) likewise that of the three basic forces — the weak, electromagnetic and strong; (vi) the non-trivial cancelation of the triangle anomalies within each family; and opening the door for (vii) the appealing concept of parity being an exact symmetry of nature at the fundamental level…

A few episodes about Abdus Salam as physicist and friend will be my contribution to the Memorial Meeting for the 90^th birthday of a physicist whose life has been devoted to the progress of science the world over…

After the last missing piece, the Higgs particle, has probably been identified, the Standard Model of the subatomic particles appears to be a quite robust structure, that can survive on its own for a long time to come. Most researchers expect considerable modifications and improvements to come in the near future, but it could also be that the Model will stay essentially as it is. This, however, would also require a change in our thinking, and the question remains whether and how it can be reconciled with our desire for our theories to be “natural”.

Abdus Salam was my PhD Advisor and I had the privilege of working with him over a long period, in fact, over more than twenty years. I first got to know him in the role of professor and supervisor at Imperial College, London, but starting in the 1980s I also interacted with him at the ICTP in Trieste, Italy, which he had founded in the early 1960s and which subsequently was named after him. We also co-organized (together with Jogesh Pati and Yu Lu) the first BCSPIN school in Kathmandu, Nepal in 1989. Abdus Salam was an exceptional human being, scientist, administrator and politician. He had tremendous strength of character as well as tenacity and discipline. He also had a powerful vision for each of his many pursuits, from science and science education, to building international networks and collaborations to Pakistans political and economic future. Abdus Salam thought in global terms and acted as a global figure well before globalism became a common term…

Abdus Salam was a great man in more than one dimension. The conception and building of the ICTP system required much more than the intelligence of a great scientist. I will stress those other facets that made him such a unique personality: the optimism that coloured his views about men and women, his love for his people and his commitment to the less favoured peoples of the world and a crucial ingredient, his deep and complex sense of ethical values that pushed him towards engagement in the political reality. Endowed with a formidable power of persuasion and a healthy lack of respect for norms or rules that are not based on justice he made a big difference on many of us and will remain as an icon for future generations. I will also describe the final touches that Salam’s collaborators and successors had to add to keep his heritage flourishing.

I begin with some memories of Abdus Salam who was my PhD supervisor. After reviewing the theory of nonlinear realisations and Kac–Moody algebras, I explain how to construct the nonlinear realisation based on the Kac–Moody algebra E₁₁ and its vector representation. I explain how this field theory leads to dynamical equations which contain an infinite number of fields defined on a space–time with an infinite number of coordinates. I then show that these unique dynamical equations, when truncated to low level fields and the usual coordinates of space–time, lead to precisely the equations of motion of 11-dimensional supergravity theory. By taking different group decompositions of E₁₁ we find all the maximal supergravity theories, including the gauged maximal supergravities, and as a result the nonlinear realisation should be thought of as a unified theory that is the low energy effective action for type II strings and branes. These results essentially confirm the E₁₁ conjecture given many years ago.

This is a tribute to Abdus Salam’s memory whose insight and creative thinking set for me a role model to follow. In this contribution I show that the simple requirement of volume quantization in space–time (with Euclidean signature) uniquely determines the geometry to be that of a noncommutative space whose finite part is based on an algebra that leads to Pati–Salam grand unified models. The Standard Model corresponds to a special case where a mathematical constraint (order one condition) is satisfied. This provides evidence that Salam was a visionary who was generations ahead of his time.

In 1978, Salam and Strathdee suggested on the basis of Froissart boundedness that curvature-squared terms should be included in the gravitational Lagrangian. Despite the presence of ghosts in such theories, the subject has remained a persistent topic in approaches to quantum gravity and cosmology. In this article, the space of spherically symmetric solutions to such theories is explored, highlighting horizonless solutions, wormholes and non-Schwarzschild black holes.

For more than 50 years, the Abdus Salam International Centre for Theoretical Physics has fostered the growth and sustainability of physics and mathematics in the developing world, benefitting hundreds of thousands of scientists. What began as a dream by its founder, Pakistani Nobel Laureate Abdus Salam, has become a first-rate international research hub connecting scientists from all corners of the globe. As the social and economic situations in many developing countries has shifted, ICTP has responded with the creation of relevant research and training programmes that continue to boost science in disadvantaged parts of the world. Today, ICTP remains a beacon of hope for scientists who aspire to greatness.

Professor Abdus Salam deeply believed that ‘scientific thought is the common heritage of all mankind’ and he had the dream that the developing world should benefit and could contribute substantially to that heritage, on par with the developed world…

It is with great pleasure, honor and privilege that I participate in this meeting to celebrate the life and achievements of Professor Abdus Salam. I thank the organizers for the kind invitation…

For all its brilliant success stories, theoretical physics is actually in a lamentable state. The best way to highlight the situation and at the same time point out that it is not difficult to do better — using action principles — is to present several examples.

Abdus Salam challenged the chiral gauge nature of the Standard Model by paving the road towards the Left-Right symmetric electro-weak theory. I describe here the logical and historical construction of this theory, by emphasising the pioneering and key role it played for neutrino mass. I show that it is a self-contained and predictive model with the Higgs origin of neutrino mass, in complete analogy with the SM situation regarding charged fermions.

The charge given to me by the organisers of the memorial meeting for Prof. Abdus Salam’s 90th birthday is to recall my personal impressions of him and review an aspect of the standard model (SM) physics related to my work. Salam was, first and foremost, a brilliant theoretical physicist whose work is still very much en vogue, currently being tested precisely by the experiments at the Large Hadron Collider (LHC). Salam was, however, equally effective as a scientific advisor to many institutions, such as IAEA and CERN, but also to the government of Pakistan as the chief scientific strategist. He was also an untiring advocate of scientific research and higher education in developing countries, which took a concrete form in the International Centre for Theoretical Physics (ICTP) in Trieste. I discuss these aspects of his scientific life seen from my perspective in the first part. In the second part of my talk, which may appear as a disjoint piece to the first, I summarise some selected topics in rare B-decays — the current flavour physics frontier. Experiments carried out over several decades are largely in agreement with the SM, thanks also to dedicated theoretical effort in their interpretation. However, this field is undergoing an anomalous phase in a number of key measurements, in particular reported by LHCb, triggering a very lively debate and model building. These anomalies, which I review here, are too numerous to be ignored, but none is individually significant enough to announce a breakdown of the SM.

In recent years, studies of long-range interacting (LRI) systems have taken center stage in the arena of statistical mechanics and dynamical system studies, due to new theoretical developments involving tools from as diverse a field as kinetic theory, non-equilibrium statistical mechanics, and large deviation theory, but also due to new and exciting experimental realizations of LRI systems. In the first, introductory, Section 1, we discuss the general features of long-range interactions, emphasizing in particular the main physical phenomenon of non-additivity, which leads to a plethora of distinct effects, both thermodynamic and dynamic, that are not observed with short-range interactions: Ensemble inequivalence, slow relaxation, broken ergodicity. In Section 2, we discuss several physical systems with long-range interactions: mean-field spin systems, self-gravitating systems, Euler equations in two dimensions, Coulomb systems, one-component electron plasma, dipolar systems, free-electron lasers. In Section 3, we discuss the general scenario of dynamical evolution of generic LRI systems. In Section 4, we discuss an illustrative example of LRI systems, the Kardar–Nagel spin system, which involves discrete degrees of freedom, while in Section 5, we discuss a paradigmatic example involving continuous degrees of freedom, the so-called Hamiltonian mean-field (HMF) model. For the former, we demonstrate the effects of ensemble inequivalence and slow relaxation, while for the HMF model, we emphasize in particular the occurrence of the so-called quasistationary states (QSSs) during relaxation towards the Boltzmann–Gibbs equilibrium state. The QSSs are non-equilibrium states with lifetimes that diverge with the system size, so that in the thermodynamic limit, the systems remain trapped in the QSSs, thereby making the latter the effective stationary states. In Section 5, we also discuss an experimental system involving atoms trapped in optical cavities, which may be modelled by the HMF system. In Section 6, we address the issue of ubiquity of the quasistationary behavior by considering a variety of models and dynamics, discussing in each case the conditions to observe QSSs. In Section 7, we investigate the issue of what happens when a long-range system is driven out of thermal equilibrium. Conclusions are drawn in Section 8.

Here I present a somewhat condensed and very personal report on SESAME (Synchrotron-light for Experimental Science and Applications in the Middle East) which is a regional “third-generation” synchrotron light source under construction in Allan, Jordan. It will be the Middle East’s first major international research center. It is expected, right now, to become operational during 2016/2017…

Since 2010 there has been a rich harvest of results on standard model physics by the ATLAS and CMS experiments operating on the Large Hadron Collider. In the summer of 2012, a spectacular discovery was made by these experiments of a new, heavy particle. All the subsequently analysed data point strongly to the properties of this particle as those expected for the Higgs boson associated with the Brout–Englert–Higgs mechanism postulated to explain the spontaneous symmetry breaking in the electroweak sector, thereby explaining how elementary particles acquire mass. This article focuses on the CMS experiment, the technological challenges encountered in its construction, describing some of the physics results obtained so far, including the discovery of the Higgs boson, and searches for the widely anticipated new physics beyond the standard model, and peer into the future involving the high-luminosity phase of the LHC. This article is complementary to the one by Peter Jenni that focuses on the ATLAS experiment.

The journey in search for the Higgs boson with the ATLAS and CMS experiments at the Large Hadron Collider (LHC) at CERN started more than two decades ago. But the first discussions motivating the LHC project dream date back even further into the 1980s. This article will recall some of these early historical considerations, mention some of the LHC machine milestones and achievements, focus as an example of a technological challenge on the unique ATLAS superconducting magnet system, and then give an account of the physics results so far, leading to, and featuring particularly, the Higgs boson results, and sketching finally prospects for the future. With its emphasis on the ATLAS experiment it is complementary to the preceding article by Tejinder S. Virdee which focused on the CMS experiment.

At the beginning of last century we witnessed the emergence of new physics, quantum theory and gravitational theory, which gave us correct understanding of the world of atoms and deep insight into the structure of universe we live in. Towards the end of the century, string theory emerged as the most promising candidate to unify these two theories…

We begin with a few words about Salam’s contribution to the growth of String Theory in India. In the technical talk we review results in SU(N) Chern–Simons plus vector matter theories in 2+1 dim in the large N limit. The dressing of charged matter by Chern–Simons gauge fields leads to anyons that interpolate between fermions and bosons and lead to a duality symmetry between fermionic and bosonic theories. The S-matrix (defined in the large N limit) besides exhibiting this duality, also exhibits novel properties due to the presence of anyons. The S-matrix is not analytic, like in Aharonov–Bohm scattering, and satisfies modified crossing symmetry relations.

If one modifies the Dirac equation in momentum space to $\left[\cancel{p}-m-\Delta m(\theta \left(p0\right)-\theta \left(-p0)\right)\theta \left(p_{\mu }^2\right)\right]\psi \left(p\right)=0$, the symmetry of positive and negative energy eigenvalues is lifted by m±Δm for a small Δm. The mass degeneracy of the particle and antiparticle is thus removed in a Lorentz invariant manner since the combinations $\theta \left(\pm p0\right)\theta \left(p_{\mu }^2\right)$ with step functions are manifestly Lorentz invariant. We explain an explicit construction of this CPT breaking term in coordinate space, which is Lorentz invariant but nonlocal at the distance scale of the Planck length. The application of this Lorentz invariant CPT breaking mechanism to the possible mass splitting of the neutrino and antineutrino in the Standard Model is briefly discussed.

Abdus Salam was a true master of 20th Century Theoretical Physics. Not only was he a pioneer of the Standard Model (for which he shared the Nobel Prize with S. Glashow and S. Weinberg), but he also (co)authored many other outstanding contributions to the field of Fundamental Interactions and their unification. In particular, he was a major contributor to the development of supersymmetric theories, where he also coined the word “Supersymmetry” (replacing the earlier “Supergauges” drawn from String Theory). He also introduced the basic concept of “Superspace” and the notion of “Goldstone Fermion”(Goldstino). These concepts proved instrumental for the exploration of the ultraviolet properties and for the study of spontaneously broken phases of super Yang– Mills theories and Supergravity. They continue to play a key role in current developments in Early-Universe Cosmology. In this contribution we review models of inflation based on Supergravity with spontaneously broken local supersymmetry, with emphasis on the role of nilpotent superfields to describe a de Sitter phase of our Universe.

We give a short overview of Newton–Cartan geometry and gravity including its matter couplings. We also present results on a new non-relativistic gravity model in three spacetime dimensions, called extended Bargmann gravity, and show that this model has matter couplings that differ from those of Newton–Cartan gravity.

In 1914 James Chadwick discovered that energy and momentum were not conserved in the beta decay of atomic nuclei. For the next 16 years this phenomenon was not understood. In 1930 Wolfgang Pauli suggested in a letter to the participants of a conference in Tuebingen, that in the beta decays not only an electron was emitted, but also a neutral particle, which could not be observed. The energy and momentum of this particle would be the observed missing energy and momentum. Enrico Fermi proposed a name for this hypothetical particle: neutrino…

It is an honor and a pleasure to have been invited to give a talk in this conference celebrating the memory of the late Professor Abdus Salam. To my regret, I did not know Professor Salam personally, but I am very aware of his work and of his impact on my area of specialization, condensed matter physics, both intellectually through his ideas on spontaneously broken symmetry and more practically through his foundation of the ICTP. Since I assume that most of this audience are not specialized in condensed-matter physics, I thought I would talk about one topic which to some extent bridges this field and the particle-physics interests of Salam, namely Majorana fermions (M.F.s). However, as we shall see, the parallels which are often drawn in the current literature may be a bit too simplistic. I will devote most of this talk to a stripped-down exposition of the current orthodoxy concerning M.F.s. in condensed-matter physics and their possible applications to topological quantum computing (TQC), and then at the end briefly indicate why I believe this orthodoxy may be seriously misleading…

Abdus Salam was a multi-dimensional man who straddled research and institution-building with enviable flair; he was both religious and iconoclastic, a true citizen of the world yet deeply nationalistic, a scientist and a lover of literature, a villager and a cosmopolitan. While the specific details of his life belong to the man alone, Salam’s rich experiences exemplify certain values, attitudes and lessons that are universal…