This lovely tribute was sent to me by fellow Bailin PhD student George Kraniotis who was unable to come to the memorial today.
My memories of David Bailin are many and still vivid in my mind since I spent 12 exciting and very productive years with him in United Kingdom. Firstly, he was my M.Sc. and D. Phil. supervisor at Sussex University during the period 1990-1995. The second phase of our collaboration (1996-2002) started in 1996 when I was hired by Alexander Love as a postdoctoral research assistant at Royal Holloway University of London and continued later at Sussex university (2001-2002). During the second phase the three of us formed a very strong research team. We published 16 original papers (12 in Physics Letters B, 2 in Nuclear Physics B and 2 in JHEP) in the fields of string phenomenology and cosmology.
Let me start with my first personal memories of David. When I was finishing my first degree at Ioannina University in Greece, I decided to start my research in string theory since I was aware, after reading a popular science article, that the theory of strings was attempting to reconcile General Relativity with Quantum Mechanics. At the same time, I had understood from my undergraduate courses that although the Standard Model of particle physics was a successful theory, yet it was not a complete story since it could not predict the mass of the electron and gravity was out of its realm. After making a personal bibliography research in Greece I realised that David Bailin was one of the world experts in this new theory. Thus I decided to apply at Sussex University for my postgraduate studies with the hope that David will become my supervisor. After I received a formal offer from the University of Sussex to enroll as an M.Sc. student on October the 2nd 1990 I travelled to Brighton. During the first week as a student I had to meet with the faculty members and find a supervisor for my M.Sc. dissertation. When I first met David I remember his welcoming smile and how polite person he was. He asked me various things about my background and then he asked me why I want to work with superstrings. I told him I am aware that the theory involves very advanced branches of mathematics however I am interested in finding out through my research about its physical relevance in Nature. Immediately David gave me to read his article entitled Why Superstrings? and we decided to meet every week to discuss my progress for the topic of my M.Sc. dissertation on string theory. I was quite pleased of course. Our common journey for the next 12 years had just started. Besides introducing me to the world of superstrings David during these first days introduced me also to the world of coffee! In our first meeting after the initial encounter he asked me if I want to drink a coffee. I was shy to tell him that I was not drinking coffee so I accepted his kind offer. To my surprise the instant coffee he made me was so tasty that since that day I joined the club of coffee lovers! He was a modest person despite the fact he was a famous theoretical physicist. He was a great teacher. Very direct with his students he asked me from the first days to call him David and not Professor Bailin. Initially it was not easy for me due to my academic undergraduate background in Greece but eventually I got used to it. He was very smart and very perceptive of the needs of his students. He inspired confidence with his knowledge and with his penetrating questions he immediately was able to have a picture of the student’s progress. I remember in February of 1991 Dr. Copeland the person responsible at Sussex at that period for the academic postgraduate admissions he asked me to meet with him in David’s office to discuss about the perspectives for me to enroll as a D.Phil, student after completing my M.Sc. course especially the financial issues. Initially we discussed about such formalities and when I thought the meeting had ended David asked me to go to blackboard and explain to both of them what I have had learned so far about string theory. I was quite surprised, and unprepared nevertheless I started writing equations on the blackboard. At some stage I mentioned that is the critical spacetime dimension of the bosonic string. David asked me to give some arguments about this. I started giving arguments about the absence of ghost states for , but then David told me but why exactly 26. I was at a loss for a few moments but then I recovered and explained that consistent quantization of the theory and the conformal symmetry (cancellation of anomalies) required the critical spacetime dimensionality to be exactly 26. After the end of the meeting (examination in fact) I learned from David that I was accepted for a D.Phil. position and he told me I did well in the board especially in the question about the dimensionality of the bosonic string. My M.Sc. project was to derive a particular Grand Unified theory the so called flipped model in the fermionic formulation of strings as formulated by Kawai et al. This project required among other things mastering the basics of group representation theory something I did pretty fast but also knowledge of number theory. In particular the derivation of the particle spectrum from the formulation required solving systems of congruences something it was completely new to me. I remember the enigmatic smile of David when I first asked him about congruences: he told me don’t you know about congruences ? It took me some effort to be able to learn solving them. I derived most of the spectrum but there were still some more involved cases that needed to be solved. David was quite rigorous and demanding and he told me you must solve all congruences and then you will start writing up your dissertation. After a few days I return in triumph to David who was pleased and he gave me the go ahead for the completion of the dissertation.
In my D.Phil. years David gave me enough space for doing independent research. He was always encouraging me to leave my mark in research but at the same time he was very supportive when it was necessary to calm me down. I learned programming from scratch. I remember David telling me when I first realized that some numerical analysis was needed in my project: George leave the calculations in paper for the moment, it is time to learn how to produce software in order to solve your renormalization group differential equations! On the other hand he was quite generous in his comments when he realized that a real progress was taking place. When I had published my second paper on the constraints the observed flavour changing neutral current process was imposing on the physical parameters of the effective supergravity from heterotic string theory he told me: George you realise that this is real life you are talking about! We celebrated the award of my D.Phil. in a Greek restaurant with live music in Brighton, David his wife Anjali, my parents and I and many of my friends in Brighton. At this point I must mention an interesting coincidence in our lives: both our fathers were tailors in profession his father’s first name was William which in Greek is usually interpreted to correspond to Vassilios my father’s first name!
During my postdoctoral years I had a very intensive interactive time with David and his long-term collaborator Alex Love. I remember vividly our trip to Philadelphia USA for the conference SUSY97. This was my first trip to USA. I was so excited. During this conference we completed (adding the final touches) our first fundamental paper on CP violation by soft supersymmetry breaking terms in orbifold compactifications and we uploaded a first version to arXiv. We were both very pleased with our results and we celebrated in an exclusive restaurant in the city. David took a nice photo of me sitting next to the well known statue of Benjamin Franklin on a bench of Philadelphia.
On the same trip I remember David expressing his firm belief on the European Community. It was Sunday morning and we had a time to spare. We took a walk on the urban Philadelphia. Near a music record shop I was mesmerised by the captivating music of Kind of Blue by Miles Davis. I told that to David so we went inside the shop to buy the cd. The seller when he understood David was an Englishman he told him that he could not understand how UK is a member of European Community since it has such a closed relationship with USA. David he responded: UK being a member of EU is able to hire people such as George here- showing me, from other EU member states ( such as Greece) who can contribute to the advancement of knowledge! The American citizen said no more!
David was very observant on the comments of his collaborators and friends. During the visits of me and Alex Love to him at Sussex for a research collaboration we used to take our lunch in the Falmer pub together with a pint of beer. On one occasion as that, the discussion involved the star wars program of USA in the era of Ronald Reagan presidency. David and Alex were quite critical of the project in general. In a surprising note to them I responded saying that perhaps the reason that the star war program was launched was not only military as a response to the cold war era but that the USA leaders of the project also had in mind the development of a defense system against a possible encounter with a large comet or asteroid that could threat Earth. David told me that I have similar ideas to Sir Fred Hoyle and he recommended to read the book by the latter: Origin of the Universe and the Origin of Religion (Anshen Transdisciplinary Lectureships in Art, Science, and the Philosophy )
A book that I really enjoyed. This is an example of how the interaction between physicists even at relaxation moments can reveal and inspire new avenues of scientific thought. Especially nowdays the relevance is more evident since astrobiology has become a new fundamental scientific discipline in the enquiries of humans on the origins of life.
He loved the Sussex surroundings very much. Besides long walks he enjoyed taking pictures of the beautiful English hill landscape around Falmer at different periods of the year in order to capture the changes of Nature at different seasons.
We also many times enjoyed the company of each other in his Hove house drinking ouzo and eating fish eggs (fish roe) a kind of caviar specialite from Vonitsa (my father’s hometown) that my father was sending me to England occasionally. Other times we spent quality time in pubs and restaurants in Hove and Brighton. On one occasion the physics department had a dinner party in a Brighton restaurant. Each one of us had the right to bring his own drinks. I brought a bottle of a very good red wine. I thought the waiter would open the bottles on table. Instead he took all bottles to open them in a separate place. I was worried but did not say anything. David read my mind and he said: George you worry that he will change the content of the bottle. He spontaneously laughed.
Our published work involved not only elementary number theory but also advanced analytic number theory such as the modular functions that were appearing in the effective supergravity Lagrangian that was consistent with modular invariance. Modular forms became a highly interesting topic for me so the field of number theory and its relation to physics became one of the subjects I got really engrossed. David invited my wife Rania and me to his house in Hove a number of times to enjoy the delicious Indian food prepared with love by Anjali. On one of these social occasions he gave me as present the book:
The Man Who Loved Only Numbers: The Story of Paul Erdös and the Search for Mathematical Truth by Paul Hoffman. I really enjoyed and have used it many times to inspire my students when I want to present examples of dedication and excellence.
Many times I enjoyed drinking tea with David in his house by the garden in Hove. Quite often in these tea breaks we discussed about the applications of number theory in cryptography bringing as an example and sharing information about the Enigma Machine and how the cryptologist’s team in Bletchley Park finally broke the code.
David encouraged my inclination to number theory aspects in many ways. When our paper in The Effect of Wilson line moduli on CP violation by soft supersymmetry breaking terms got published in Physics Letters B a week after its submission all three members of our research team were so pleased. It was a highly original and technical paper. In this paper the Igusa cusp form of genus two was involved in the construction of the effective supergravity Lagrangian. The original use of this highly non-trivial function for the first time in the string theory literature was certainly a reason for some pride for the achievement. David once more was very generous in his comments to me by telling me: George, there are only two physicists in the world who are really experts in these Igusa functions, you and a colleague of ours in Germany (S.Stieberger). The latter had been cited in our work.
In summer 1998 we shared some very beautiful moments in Oxford in a conference there (SUSY 98). Besides the exciting scientific part of our visit we spent some quality time there together with colleagues and friends in the local pubs and cafes discussing physics enjoying the atmosphere of Oxford. David emitted a kind of beautiful warmth with his acquaintances and friends. As a part of the social program of the conference we attended an opera in the city. Before the start of the performance I noticed a luxurious chair in the middle of the scene. Being in a good humour I asked David for who is this chair? David being also in a good humour he replied: for you! We both smiled happily and enjoyed the rest of the evening.
In spring of 2000, I spent a month at Cern with David as a visiting scientist. During this month we completed a PLB paper: CP violation including universal one loop corrections and heterotic M theory . Besides work we had time for enjoying ourselves. I remember vividly dinning with David in Café de Paris restaurant in Geneva where we ate very high quality beef steaks. I enclose a picture of me and David from this night. We also enjoyed walking in the surrounding mountains with the company of other colleagues. I enclose two pictures from such mountain walks. In the photos besides David and me appear two other ex students of David: Thomas Dent and Malcolm Fairbairn.
In the years 2001-2002 we produced and published some pioneering and influential work in the exciting field of intersecting Dirichlet branes. Specifically, we produced semi-realistic standard-like models in the context of the large extra dimensions string gravity scenario. I believe we were the first group that solved analytically in a general way the string tadpole equations and the constraints arising from a generalised Green-Schwartz anomaly cancellation mechanism.
Besides being my supervisor, mentor, teacher, research collaborator, a friend, David he was also my best man. He was the best man together with Phil Valder in my marriage with Ourania Kraniotis in a beautiful ceremony in Weybridge Register Office /Surrey County Council on October the 18th 2001. All of us have very fond memories of that day. I sent some photos from this happy day. When we received the marriage certificate David told us both: never lose it! David was also very happy when our son Vassilis was born in Brighton!
Many times in our informal discussions David had mentioned that a professional physicist in his career must necessarily spend some time working in USA in order to gain experience on how US physicists collaborate in doing research. Indeed, after my research experiences in USA working as a postdoctoral research fellow at Texas A&M university in the period 2004-2006 , I couldn’t agree more (with David).
In 2010 David introduced me to the world of Facebook! We became friends in the platform and many times we exchange personal communication there. I remember how happy I felt when I received a like from David for my uploads. Especially each time he added a like on my scientific uploads sharing my recent publications in gravitational physics and black holes constituted an additional gratification for me!
In retrospect I feel very lucky that I met David and spent twelve exciting years with him in United Kingdom. On the other had I feel sad and regret that after I left England in April 2002 I never met in person with David again. Of course we had frequent communication exchanging emails and latter messages in Facebook but still this cannot substitute the personal live contact. Many times humans make the mistake to believe that their beloved ones will always be physically around. Especially when their beloved ones have been larger than life as David was. Unfortunately life is cruel in this respect. David left us suddenly last March, resting now in a neighbourhood of Stars. However, people never die as long as their living beloved ones keep remembering them. I will miss you dearly David and I will honour your memory forever.