arXiv subjects

Felipe Figueroa

Publications and source records attributed to Felipe Figueroa.

7 recordsLinked to original sources

arXiv2026

Spinor-helicity formalism for continuous-spin particles

We propose a new formulation of continuous-spin particles (CSP) with the help of a single two-component spinor to build asymptotic states. This formulation allows to write down amplitudes in a straightforward way, similar to the massless spinor-helicity approach. The helicity states naturally emerge upon decomposing into components of a fixed homogeneity degree. We show that CSP amplitudes can be understood as the infinite-spin limit of amplitudes of massive particles and, similarly to the scattering of black holes, a certain universal factor exponentiates. In analogy with the recent discovery of collinear amplitudes in self-dual theories, we find nontrivial CSP collinear amplitudes where the collinear fractions are constrained by the dimensionful parameter characterising the various continuous-spin particles.

hep-th↗

arXiv2025

Regge trajectories for UV completions of graviton scattering from polynomial boundedness

We study graviton scattering amplitudes. Assuming they are UV completed by a theory of weakly coupled massive higher spins, we demonstrate that the UV completion must possess infinitely many Regge trajectories, and thus they are forced to have a stringy spectrum. We extend and simplify a previous proof by some of us for open-string like states to the case of external gravitons. In the present new proof, we trace the need for infinitely many trajectories to the constraint of polynomial boundedness, ultimately tied to causality. We further present numerical results based on the stringy ansatz of H\"aring-Zhiboedov, which illustrates how single-trajectory-like solutions actually emerge as extremal solutions of numerical bootstrap. In our numerics, these trajectories curiously show up as numerically very large \textit{sister} trajectories. We provide solid evidence that the solutions are spurious as they appear to admit a divergent limit for infinite ansatz size.

hep-th↗

arXiv2025

Unraveling the Spectrum of the Open String

We construct a large portion of the massive spectrum of the open bosonic string using light-cone quantization, providing explicit oscillator realizations for individual single-particle states as well as for full Regge trajectories. We show how combinations of transverse oscillators organize into irreducible SO(25) representations, and provide an algorithm for constructing them level by level. We then develop a general method to "climb" the spectrum-adding oscillators in a controlled way that generates entire Regge trajectories from a finite set of seed states. Remarkably, the coefficients determining each state's oscillator composition depend on the level in a simple way, allowing closed-form expressions for infinitely many states. Beyond individual trajectories, we explore internal regularities of the spectrum and establish relations among families of trajectories, extending the concept of a Regge trajectory to more general constructions. Our results expose a highly ordered and recursive structure underlying the open-string spectrum, suggesting that its massive excitations form an algorithmically constructible network. The framework presented here lays the groundwork for computing three-point amplitudes of arbitrary massive states, the essential building blocks of string interactions, which we tackle in upcoming work.

hep-th↗

arXiv2024

On the number of Regge trajectories for dual amplitudes

Regge poles connect the analytic structure of scattering amplitudes, analytically continued in spin, to the high-energy limit in momentum space. Dual models are expected to have only Regge poles, and string theory suggests there should be an infinite number of them. In this study, we investigate the number of Regge trajectories these models may have. We prove, based solely on crossing symmetry and unitarity, that meromorphic amplitudes, with or without subtractions, cannot produce a reggeizing amplitude if they contain any finite number of Regge trajectories. We argue that this should exclude the existence of such amplitudes altogether. Additionally, we develop and apply a linear programming dual bootstrap method to exclude these amplitudes directly in momentum space.

hep-th↗

arXiv2024

The Regge bootstrap, from linear to non-linear trajectories

We present a numerical linear programming bootstrap to construct dual model scattering amplitudes. Dual models describe tree-level exchanges of higher spin resonances in theories like string theory and large $N$ gauge theories. Despite being very simple objects, their numerical bootstrap has proven challenging due to slow convergence of the infinite sums over resonances. Our bootstrap succeeds thanks to an efficient parametrization of the amplitude in terms of Mandelstam-Regge poles and the use of combined regions that make crossing symmetry constraining. Along the way, we discover and conjecture a property of "super-unitarity" of the Veneziano amplitude, which we use to keep a linear problem. As results, we present first the study of a class of string-like amplitudes with linear trajectories, for which we observe that the Veneziano amplitude lies at a preferred location, at the bottom of a pit, which minimizes crossing. Then, we introduce a toy-model deformation to non-linear trajectories, mimicking some features of QCD, for which our algorithm also detects a clear pit. This gives compelling evidence that our bootstrap is able to produce amplitudes that can exhibit non-trivial phenomenological features.

hep-th↗

arXiv2022

One-loop unquenched three-gluon and ghost-gluon vertex in the Curci-Ferrari model

In this article we study the unquenched three-gluon and ghost-gluon vertex in all momentum range going from the ultraviolet to the infrared regime using the Curci-Ferrari model at one-loop in Landau gauge as an extension of the results presented in \cite{Pelaez:2013cpa}. Results are compared with recent lattice data for $SU(3)$ in the unquenched case. This calculation is a pure prediction of the model because it does not require fixing any parameter once two-point functions are fitted. An analysis of the influence of dynamical quarks in the position of the zero crossing of the three-gluon vertex is presented. Due to the recent improvements in infrared lattice data for the quenched three-gluon correlation function \cite{Aguilar:2021lke} we also redo the comparison between our one-loop results in this limit and the lattice obtaining a very good match.

hep-th↗

arXiv2022

On the unitarity and low energy expansion of the Coon amplitude

The Coon amplitude is a deformation of the Veneziano amplitude with logarithmic Regge trajectories and an accumulation point in the spectrum, which interpolates between string theory and field theory. With string theory, it is the only other solution to duality constraints explicitly known and it constitutes an important data point in the modern S-matrix bootstrap. Yet, its basics properties are essentially unknown. In this paper we fill this gap and derive the conditions of positivity and the low energy expansion of the amplitude. On the positivity side, we discover that the amplitude switches from a regime where it is positive in all dimensions to a regime with critical dimensions, that connects to the known $d = 26, 10$ when the deformation is removed. En passant, we find that the Veneziano amplitudes can be extended to massive scalars of masses up to $m^2 = 1/3$, where it has critical dimension 6.3. On the low-energy side, we compute the first few coupligs of the theory in terms of $q$-deformed analogues of the standard Riemann zeta values of the string expansion. We locate their location in the EFT-hedron, and find agreement with a recent conjecture that theories with accumulation points populate this space. We also discuss their relation to low spin dominance.

hep-th↗