Narrow Results

The use of a non-Riemannian measure of integration in the action of strings and branes allows the possibility of dynamical tension. In particular, lower dimensional objects living in the string/brane can induce discontinuities in the tension: the effect of pair creation on the string tension is studied. We then investigate the role that these new features can play in string and brane creation and growth. A mechanism is studied by means of which a scalar field can transfer its energy to the tension of strings and branes. An infinite-dimensional symmetry group of this theory is discussed. Creation and growth of bubbles in a formulation that requires mass generation for the bulk gauge fields coupled to the branes is also discussed.

Starting with a Zipoy–Voorhees line element, we construct and study the three-parameter family of solutions describing a deformed black string with arbitrary tension.

In this paper we review the conditions for the validity of the gauge/gravity correspondence in both supersymmetric and nonsupersymmetric string models. We start by reminding what happens in type IIB theory on the orbifolds ℂ²/ℤ₂ and ℂ³/(ℤ₂ x ℤ₂), where this correspondence beautifully works. In these cases, by performing a complete stringy calculation of the interaction among D3-branes, it has been shown that the fact that this correspondence works is a consequence of the open/closed duality and of the absence of threshold corrections. Then we review the construction of type 0 theories with their orbifolds and orientifolds having spectra free from both open and closed string tachyons and for such models we study the validity of the gauge/gravity correspondence, concluding that this is not a peculiarity of supersymmetric theories, but it may work also for nonsupersymmetric models. Also in these cases, when it works, it is again a consequence of the open/closed string duality and of vanishing threshold corrections.

Recent advances in the study of microstates for $\frac{1}{16}$-BPS black holes have inspired renewed interest in the analysis of heavy operators. For these operators, traditional techniques that work effectively in the planar limit are no longer applicable. Methods that are sensitive to finite N effects are required. In particular, trace relations that connect different multi-trace operators must be carefully considered. A powerful approach to tackling this challenge, which utilizes the representation theory of the symmetric group, is provided by restricted Schur polynomials. In this paper, we develop these methods with the goal of providing the background needed for their application to $\frac{1}{16}$-BPS black holes.

Braneworld models are interesting theoretical and phenomenological frameworks to search for new physics beyond the standard model of particles and cosmology. In this work, we discuss braneworld models whose gravitational dynamics is governed by teleparallel $f(T)$ gravities. Here, we emphasize a codimension two-axisymmetric model, also known as a string-like brane. Likewise, in the 5D domain-wall models, the $f(T)$ gravitational modification leads to a phase transition on the perfect fluid source providing a brane-splitting mechanism. Furthermore, the torsion changes the gravitational perturbations. The torsion produces new potential wells inside the brane core leading to a massless mode more localized around the ring structures. In addition, the torsion keeps a gapless nonlocalizable and a stable tower of massive modes in the bulk.

The bosonic large-$N$ master field of the IIB matrix model can, in principle, give rise to an emergent classical spacetime. The task is then to calculate this master field as a solution of the bosonic master-field equation. We consider a simplified version of the algebraic bosonic master-field equation and take dimensionality $D=2$ and matrix size $N=6$. For an explicit realization of the pseudorandom constants entering this simplified algebraic equation, we establish the existence of a solution and find, after diagonalization of one of the two obtained matrices, a band-diagonal structure of the other matrix.

We give a brief overview of work by and in collaboration with Julius Wess in his noncommutative era.