# Gabriele Veneziano Elementary Particles, Gravitation and Cosmology (2004-2013)

Gabriele Veneziano was born on September 7, 1942 in Florence (Italy). After completing his high-school studies (at the Liceo Scientifico “Leonardo da Vinci,” Florence) he entered the University of Florence in 1960, where he started studying physics. He took his degrees (Laurea in Fisica) in 1965 defending a thesis on the applications of group theory to strong interactions, under the supervision of Professor Raoul Gatto. A short paper extracted from his thesis became his first scientific publication (here, and in what follows, the quoted numbers refer to the list of publications of Gabriele Veneziano reported at the end of this chapter).

After graduating he won a scholarship of Angelo della Riccia to carry out research in the group directed by Raoul Gatto, who had gathered in Florence a number of brilliant young theorists (like Guido Altarelli, Franco Buccella, Giovanni Gallavotti, Luciano Maiani, and Giuliano Preparata, to mention a few). During that period he wrote a paper on saturation of current algebra sum rules that attracted the attention of Professor Sergio

Fubini. Meanwhile (after a conversation with Professor Giulio Racah) he had decided to continue his studies toward a PhD, choosing to apply to the Weizmann Institute of Science in Rehovot (Israel). In July 1966 he got married to Edy Pacifici and, after their honeymoon in Venice, they moved together to Israel.

His official advisor at the Weizmann Institute was Professor Harry J. Lipkin; however, his research activity was mainly carried out under the supervision of Professor Hector Rubinstein (see the contribution of Hector Rubinstein to this volume). In Israel he quickly completed his PhD studies,getting the degree at the end of 1967. The PhD thesis was largely based on his research with Rubinstein and on work done in collaboration

with Marco Ademollo (professor in Florence and visiting Harvard at that time) and Miguel Virasoro (who had joined the Weizmann group in the spring of 1967). That work developed important ideas initiated by Sergio Fubini and collaborators on a bootstrap approach to strong interactions based on “superconvergence” and “duality”.

At the beginning of 1968 he was offered several postdoctoral positions in the United States, and he decided to accept the invitation of MIT (Boston) to join the newly formed Center for Theoretical Physics to which Sergio Fubini and Steven Weinberg had recently moved. Before starting the MIT appointment he spent the whole summer at the TH Division of CERN, where he completed the celebrated paper “Construction of a crossing-symmetric, Regge behaved amplitude for linearly-rising trajectories”, in which he proposed the scattering amplitude that bears his name, and that is usually regarded as marking the birth of string theory. The model presented in his seminal paper incorporated most of the desired ingredients of an S-matrix theory of

strong interactions, and it was largely quoted at the Vienna Conference on High Energy Physics, at the end of that summer.

At MIT he mainly worked with Sergio Fubini to develop generalizations of his earlier work that became known as “dual resonance models.” Their work paved the way to the re-interpretation of such models as a theory of

strings. In fact, some of the crucial features of string theory, such as the exponential degeneracy of the states, the concept of “Fubini–Veneziano” vertex operator, and the algebraic structure underlying the Virasoro operators, were introduced by them in that period (see the contributions of Paolo di Vecchia, Adam Schwimmer, and Miguel Virasoro to this volume).

In that period he also spent a summer at the Lawrence Berkeley Laboratory (California), where he contributed to an influential paper on the “twist” operator. After the birth of his son Ariel (September 1970), and a one-term visit at the Institute for Advanced Studies in Princeton, he undertook a program invoking topological ideas in order to implement unitarity in the context of dual resonance models. This led, in particular, to a model for the “Pomeron”, later developed by other researchers into the so-called dual parton model.

In 1972 he came back to the Weizemann Institute as a full professor. In the subsequent 4 years he also spent extended periods at CERN, pursuing the development of the topological unitarization ideas, meanwhile interpreted by Gerard ’t Hooft as a 1/N expansion.

In 1976 he joined the TH Division of CERN, first as a scientific associate, then as a junior staff member (1977–1978), and, finally, as a senior staff member.

Later he became Head of the TH Division (1994–1997). The beginning of this period was marked by the birth of his daughter Erika (July 1976), and by a change of direction of his research interests.

He started to work, in particular, on large N expansions in quantum chronodynamics (QCD), its applications to baryon dynamics, and Bose–Einstein effects in jet physics (see the contribution of Alberto Giovannini to this volume). Together with Daniele Amati and Roberto Petronzio, he proved the factorization theorem on collinear singularities in perturbative QCD, which forms the basis of the QCD parton model (see the contribution of Roberto Petronzio to this volume). This brought him naturally to devote his activity to the physics of QCD jets, writing some seminal papers with Kenichi Konishi and Akiwa Ukawa (the KUV jet calculus), and with Daniele Amati (pre-confinement) (see the contributions of Marcello Ciafaloni and Giuseppe Marchesini to this

volume).

Turning his attention to non-perturbative aspects of QCD, he tackled the U(1) axial problem for a 1/N perspective, arriving at the celebrated (and even recently confirmed) Witten–Veneziano formula. Related studies led to an estimate of the electric dipole moment of the neutron induced by a non-vanishing QCD θ-angle. These results were encoded into an effective Lagrangian formalism developed with Paolo di Vecchia.

The effective Lagrangian formalism was later applied to supersymmetry (SUSY) Yang–Mills theories and SUSY QCD, where the non-perturbative breakdown of non-renormalization theorems was first suggested.

The superpotentials derived in those papers, in collaboration with Thomasz Taylor and Shimon Yankielowicz, are still being widely used and cited (often under some other names) in many contexts. The indications

of those papers were confirmed by explicit calculations that he later performed with Giancarlo Rossi and collaborators, and that are summarized in (see the contribution of Giancarlo Rossi to this volume). In that period he also pointed out the possible formulation of SUSY Yang–Mills theories in the lattice, and suggested an implementation that is still being attempted.

When string theory was recognized as a promising candidate to unify gravity and gauge interactions (i.e., after the so-called Green–Schwarz revolution in 1984) he came back to the theory that he had to abandon (not without regret) when it appeared inappropriate as a theory of strong interactions. His studies (with various collaborators, including Amit Giveon, Jnan Maharana, and Eliezer Rabinovici) first concentrated on the following directions: the physical consequences of a fundamental length, the emergence of new field-theoretic and “stringy” symmetries (see the contributions of Jnan Maharana and Eliezer Rabinovici to this volume), the possible phenomenological consequences of a light dilaton, and a background field approach to the study of the T-duality symmetry.

A more substantial activity in that period concerned the study of gedanken experiments on trans-Planckian string collisions, in collaboration with Daniele Amati and Marcello Ciafaloni. The main purpose of such studies was the understanding of how string theory may reproduce general-relativistic results at large distances, while providing important corrections at stringsize distances. The works possibly have applications to an effectively modified uncertainty principle and to the problem of “information loss” in blackhole physics (see the contribution of Daniele Amati to this volume).

While working on string theory he kept alive his interest in the subject of strong interaction phenomenology, producing works on the “spin of the proton” puzzle (see the contribution of Graham Shore to this volume), and

on semi-inclusive hard processes (see the contribution of Luca Trentadue to this volume).

Triggered by his wish to find novel applications of string theory (and new possible ways to test it), he then turned his interest toward primordial cosmology and its theoretical and observational challenges. Starting

from the study of duality symmetries in cosmological backgrounds (see the contribution of Krzysztof Meissner to this volume) he proposed, in collaboration with Maurizio Gasperini, the so-called pre-big bang scenario, which attracted considerable interest in the astrophysical community, stimulating the studies of new mechanisms of inflation (see the contribution of Maurizio Gasperini to this volume). The multiple implications

of this scenario were the object of many subsequent studies with various collaborators (see the contributions of Alessandra Buonanno, Thibault Damour, Massimo Giovannini, and Carlo Ungarelli to this volume). Of

particular relevance were the phenomenological predictions concerning the generation of magnetic seeds, the enhanced production of primordial gravitational waves, and the possible axionic origin of the cosmic microwave

background (CMB) anisotropy, opening a unique observational window on string/Planck-scale physics.

Encouraged by the possibility of concrete experimental verifications of such a string cosmology scenario, he and Maurizio Gasperini also tackled the problem of understanding (or re-interpreting), in such a context, the big bang singularity, by applying either quantum cosmology techniques (in collaboration with Jnan Maharana), or higher-order string corrections (in collaboration with Michele Maggiore), or non-local effects of the quantum back reaction (in collaboration with Massimo Giovannini). The study of the high-curvature, strong-coupling regime (also appropriate to brane inflation, see the contribution of Henry Tye to this volume) led him to obtain, as a byproduct, unexpected results on entropy in collaboration with Ram Brustein (see the contribution of Ram Brustein to this volume), and unexpected connections with black-hole physics, in collaboration with

Thibault Damour. Later developments of the pre-big bang scenario also led to interesting (and testable, in principle) interpretations of the presently observed cosmic acceleration.

His most recent interests are mainly focused again on the 1/N expansion, with two different ramifications. The first concerns a new version of such expansion, capable of connecting QCD to supersymmetric theories, developed in collaboration with Adi Armoni and Mikhail Shifman. The obtained predictions for one-flavor QCD, in particular, have been confirmed by subsequent (phenomenological or lattice) computations (see the contribution of Adi Armoni and Mikhail Shifman to this volume). The second, developed in collaboration with Enrico Onofri and Jacek Wosiek, deals with a Hamiltonian approach to large N dynamics, which, while still limited to quantum mechanics, has already produced interesting results in different branches of mathematical physics, like combinatorics and statistical mechanics.

Since 2004 he holds the prestigious Chair of Elementary Particles, Gravitation and Cosmology at the Collège de France, in Paris.