1,721,041 research outputs found
Roberto Petronzio and the "Tor Vergata" Theory Group
Full text linkI present some recollections of the first years, in the 1980s and 1990s,
of the Theoretical Physics Group of the University of Rome “Tor Vergata”. I will
focus on my interactions with Roberto, which were particularly intense when I was
helping him with the key course on “Quantum and Statistical Mechanics”, but also
on the role that he played in shaping the very structure of the group, and of the
University at large
The incomplete revolutions of String Theory
Full text linkvol35 / no3-4 / anno2019 > 47 percorsi The Incomplete Revolutions of String Theory Augusto SAGNOTT I Scuola Normale Superiore, Pisa, Italy INFN, Sezione di Pisa, Pisa, Italy DESY, Hamburg, Germany 1 Quantum fields and particles Our current understanding of the Fundamental Interactions rests on Quantum Field Theory. This setting affords a novel incarnation of the point particle idea, which has nurtured Physics since the time of Galileo Galilei and the subsequent birth of Newtonian Mechanics. Rigid bodies, strings, membranes and fluids are but variations on this theme, and point particles have also provided important clues on light and waves. When Quantum Mechanics found its place in a relativistic picture, in the 1930’s, particle-wave duality found a concrete realization in Quantum Field Theory, where masses and momenta qualify field quanta together with a novel attribute, spin. Atomic Physics had indeed provided, since the early 1920’s, compelling If one tried to get a palatable picture of Electromagnetism, it would be natural to hear from an expert about charges, flux lines, potentials and waves. These are subtle concepts, and yet they can convey some valuable intuition on these phenomena, despite the intricacies of the underlying Mathematics. Similar questions about General Relativity would probably bring up falling bodies, the Equivalence Principle and deformations of the fabric of spacetime where planets slide along their orbits. String Theory, however, is still a very different matter, and experts have a hard time defining it. One could say that strings replace particles, as we shall try to explain, but in our current view particles emerge from fields, whose geometry underlies their interactions. As we shall see, appealing to such geometrical principles within the low-energy Supergravity has provided unprecedented glimpses of a unified view of Nature that transcends not only strings but our very picture of spacetime. Yet, we lack somehow satisfactory answers to some basic questions, which ought to have preceded all this. What replaces the principles of General Relativity in String Theory? What do strings tell us about spacetime at short distances? Why is our Universe the way it seems? String Theory is today an awesome unfinished monument, whose roots remain elusive despite decades of intense effort. While this brings about some distress, it also makes the subject mysterious, challenging and highly fascinating. In the following, I shall describe the origin of this unusual situation, while also trying to address some future prospects
On boundaries, charges and Fermi fields
Full text linkWe address some general issues related to torsion and Noether currents for Fermi fields in the presence of boundaries, with emphasis on the conditions that guarantee charge conservation. We also describe exact solutions of these boundary conditions and some implications for string vacua with broken supersymmetry
On the systematics of open-string theories
No full textWe clarify the role of the fusion algebra in determining the interactions and the Chan-Paton symmetry of open-string models. Adapting the internal symmetry to the fusion algebra yields corresponding patterns of symmetry breaking, which we illustrate in a number of examples
Twist symmetry and open-string Wilson lines
No full textThe Mobius amplitude plays an important role in open-string theories, since it determines which sectors of a given model consist of unoriented open strings. It also fixes the Chan-Paton representations of all their states, according to the behavior under the interchange of the ends of open strings ("twist"). In this paper we discuss the role played by conventional Wilson lines in Chan-Paton symmetry breaking, and we show that the presence of an extended symmetry algebra allows, in general, a number of choices for the behavior of massive states under twist. This freedom may be ascribed to additional discrete Wilson lines, and yields consistent modifications of the group assignments, that are illustrated in a number of examples
On warped string vacuum profiles and cosmologies. Part I. Supersymmetric strings
Full text linkWe investigate in detail solutions of supergravity that involve warped products of flat geometries of the type Mp+1× R × TD−p−2 depending on a single coordinate. In the absence of fluxes, the solutions include flat space and Kasner-like vacua that break all supersymmetries. In the presence of a symmetric flux, there are three families of solutions that are characterized by a pair of boundaries and have a singularity at one of them, the origin. The first family comprises supersymmetric vacua, which capture a universal limiting behavior at the origin. The first and second families also contain non-supersymmetric solutions whose behavior at the other boundary, which can lie at a finite or infinite distance, is captured by the no-flux solutions. The solutions of the third family have a second boundary at a finite distance where they approach again the supersymmetric backgrounds. These vacua exhibit a variety of interesting scenarios, which include compactifications on finite intervals and p + 1-dimensional effective theories where the string coupling has an upper bound. We also build corresponding cosmologies, and in some of them the string coupling can be finite throughout the evolution
On warped string vacuum profiles and cosmologies. Part II. Non-supersymmetric strings
Full text linkWe investigate the effects of the leading tadpole potentials of 10D tachyon-free non-supersymmetric strings in warped products of flat geometries of the type Mp+1× R × T10−p−2 depending on a single coordinate. In the absence of fluxes and for p < 8, there are two families of these vacua for the orientifold disk-level potential, both involving a finite internal interval. Their asymptotics are surprisingly captured by tadpole-free solutions, isotropic for one family and anisotropic at one end for the other. In contrast, for the heterotic torus-level potential there are four types of vacua. Their asymptotics are always tadpole-dependent and isotropic at one end lying at a finite distance, while at the other end, which can lie at a finite or infinite distance, they can be tadpole-dependent isotropic or tadpole-free anisotropic. We then elaborate on the general setup for including symmetric fluxes, and present the three families of exact solutions that emerge when the orientifold potential and a seven-form flux are both present. These solutions include a pair of boundaries, which are always separated by a finite distance. In the neighborhood of one, they all approach a common supersymmetric limit, while the asymptotics at the other boundary can be tadpole-free isotropic, tadpole-free anisotropic or again supersymmetric. We also discuss corresponding cosmologies, with emphasis on their climbing or descending behavior at the initial singularity. In some cases the toroidal dimensions can contract during the cosmological expansion
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