arXiv subjects

Federico Castellani

Publications and source records attributed to Federico Castellani.

8 recordsLinked to original sources

arXiv2026

Hagedorn temperature from holography: rotating and charged systems

Using the string/field theory correspondence as a tool, we study the dependence of the Hagedorn temperature of strongly coupled, planar gauge theories on angular velocities and chemical potentials for $U(1)$ global currents. Our results are obtained from an interplay of world-sheet semiclassical quantization methods and target space low energy effective ones. The Hagedorn temperature is given as an expansion in the inverse (large) 't Hooft coupling limit. Working to quadratic order in the fluctuations, the world-sheet analysis provides the leading, the next-to-leading and part of the next-to-next-to leading order terms. In particular, it captures the NNLO $\log 2$ terms which are due to the contributions of non-zero modes to the zero-point energy. These modes are not accounted for by the effective approach, within which they have to be included by hand using suitable educated guesses. On the other hand, the effective methods allow to compute in a relatively easy way the missing NNLO pieces (and even further subleading corrections), which could be accounted for from the world-sheet approach only working at quartic (or higher) order in the fluctuations. We present general results and several examples in various dimensions, including both confining models and conformal field theories on spheres (such as $\mathcal N=4$ SYM and ABJM) dual to string theories on global $AdS$ spaces.

hep-th↗

arXiv2026

Bremsstrahlung function from Goldstone bosons in AdS$_2$

We study quantum field theory on the AdS$_2$ worldsheet of the fundamental string dual to the half-BPS Wilson line of $\mathcal{N}=4$ super Yang-Mills. We consider a recently proposed gauge-fixed string fluctuation Lagrangian around the AdS$_2$ minimal surface, and focus on the nonlinearly realized $SO(6)/SO(5)$ symmetry. The boundary two-point function of the associated tilt operators, whose normalization coefficient is proportional the Bremsstrahlung function, can be related to the bulk two-point function of the broken-symmetry Noether current through the boundary operator expansion. We evaluate the one-loop diagrams contributing to the current correlator, discussing the role of dimensional regularization and recovering the known strong-coupling correction to the Bremsstrahlung function directly from AdS$_2$ worldsheet quantum field theory.

hep-th↗

arXiv2025

Vacuum configuration of winding superstrings from non-standard semiclassical quantization

Semiclassical quantization techniques are unreliable, if the magnitude of the quantum fluctuations becomes comparable with a classical background scale. This is the case, for example, for superstrings at temperatures close to the Hagedorn temperature. Here, we propose a non-standard treatment which aims to extend the semiclassical approach for type-II superstrings to such cases. This allows us to provide a well-posed reformulation of recent computations of the Hagedorn temperature in a large class of confining gauge theories. Along the way, we fill a gap in the literature by proving that the standard semiclassical one-loop partition function of the Green-Schwarz superstring can be made finite, by means of a suitable choice of integration measures, for any background worldsheet in a target spacetime satisfying the (type-IIA) supergravity field equations.

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arXiv2024

TsT-Generated Solutions in Type IIB Supergravity from Twisted Compactification of AdS$_5\times$T$^{1,1}$

This paper investigates marginal and dipole TsT transformations of a seed type IIB supergravity solution dual to a supersymmetry-preserving deformation of the Klebanov-Witten 4d SCFT. To explore key properties of the deformed theories, we holographically analyze various observables, including Wilson loops, 't Hooft loops, Entanglement Entropy, and holographic central charge flow. Moreover, we focus on detecting which of these observables are affected by the dynamics of the Kaluza-Klein (KK) modes resulting from the circle compactification.

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arXiv2024

Holography for Confined and Deformed Theories: TsT-Generated Solutions in type IIB Supergravity

In this paper, we present a series of solutions of type IIB Supergravity, obtained through the TsT deformation of a seed background that is holographically dual to ${\cal N}=4$ Super Yang-Mills theory compactified on a circle (with a twist). We explore various holographic observables, focusing on disentangling the contributions of confinement, marginal deformations, and their interplay. Additionally, we provide a detailed analysis of how certain observables are influenced by the dynamics of the Kaluza-Klein (KK) modes arising from the circle compactification. Our results offer an improved understanding of the connections between the type IIB deformed backgrounds and the dual QFTs.

hep-th↗

arXiv2024

Hagedorn temperature in holography: world-sheet and effective approaches

We provide general results on the Hagedorn temperature of planar, strongly coupled confining gauge theories holographically dual to type II superstring models on curved backgrounds with Ramond-Ramond and Kalb-Ramond fluxes and non-trivial dilaton. For exact backgrounds the Hagedorn temperature is determined up to next-to-next-to-next-to-leading order (NNNLO) in an expansion in $\alpha'$; in all the other cases the results can be safely trusted up to NNLO. To reach these goals we exploit two complementary approaches. On the one hand, we perform an extrapolation to the Hagedorn regime of world-sheet results obtained from the semiclassical quantization of string configurations winding around the compact Euclidean time direction. En passant, we provide a detailed derivation of the fermionic part of the world-sheet spectrum, which is hard to find in the literature. On the other hand, we perturbatively solve the equations of motion for the thermal scalar field corresponding to the lightest mode of the winding string, which in flat space becomes tachyonic above the Hagedorn temperature. The interplay between different approaches is surely convenient, but we provide insights about a possible derivation of the whole NNLO correction to the Hagedorn temperature from a pure world-sheet perspective; furthermore, we determine the effective mass of the thermal scalar from the world-sheet in full generality.

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arXiv2024

Nucleon electric and magnetic polarizabilities in Holographic QCD

We analyze the resonance contributions to the generalized Baldin sum rule, namely the sum of the generalized electric and magnetic nucleon polarizabilities $\alpha_E(Q^2)$ and $\beta_M(Q^2)$, within the Holographic QCD model by Witten, Sakai, and Sugimoto (WSS). In particular, we account for the contributions from the first low-lying nucleon resonances with spin 1/2 and 3/2 and both parities. After having extrapolated the WSS model parameters to fit experimental data on baryonic observables, we compare our findings with alternative predictions in literature, finding a qualitative agreement with all of them. Moreover, at least for the proton case, where data are available, our results are in qualitative accordance with resonance contributions extracted from experimental nucleon-resonance helicity amplitudes.

hep-ph↗

arXiv2023

Resonance contributions to nucleon spin structure in Holographic QCD

We study polarized inelastic electron-nucleon scattering at low momentum transfer in the Witten-Sakai-Sugimoto model of holographic QCD, focusing on resonance production contributions to the nucleon spin structure functions. Our analysis includes both spin $3/2$ and spin $1/2$ low-lying nucleon resonances with positive and negative parity. We determine, in turn, the helicity amplitudes for nucleon-resonance transitions and the resonance contributions to the neutron and proton generalized spin polarizabilities. Extrapolating the model parameters to realistic QCD data, our analysis, triggered by recent experimental results from Jefferson Lab, agrees with the observation that the $Δ(1232)$ resonance gives the dominant contribution to the forward spin polarizabilities at low momentum transfer. The contribution is negative and tends to zero as the momentum transfer increases. As expected, the contribution of the $Δ(1232)$ to the longitudinal-transverse polarizabilities is instead negligible. The latter, for both nucleons, turn out the be negative functions with zero asymptote. The holographic results, at least for the proton where enough data are available, are in qualitative agreement with the resonance contributions to the spin polarizabilities extracted from experimental data on the helicity amplitudes.

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