String Theory Research Articles

Relating gauge gravity to string theory through obstruction

Relating gauge gravity to string theory through obstruction

Matrix theory reloaded: a BPS road to holography

We revisit the decoupling limits that lead to matrix theories on D-branes. We highlight the BPS nature of these limits, in which the target space geometry becomes non-Lorentzian and wrapped D-branes experience instantaneous gravitational forces. Applied to curved D-brane geometries, we show that a single BPS decoupling limit induces the bulk near-horizon limit leading to AdS/CFT. By consecutively applying two such limits, we systematically generate further examples of holography, including novel versions with non-Lorentzian bulk geometry. Uplifted to M-theory, we are led to a unified framework where each BPS decoupling limit corresponds to a Discrete Light Cone Quantisation (DLCQ). We conjecture that a DLCQn/DLCQm correspondence, with m > n, captures the notion of holography in string theory. In particular, AdS5/CFT4 can be viewed as an example of DLCQ0/DLCQ1, with the extra DLCQ on the field theory side corresponding to the near-horizon limit in the bulk geometry. We further show that undoing these BPS decoupling limits can be viewed as deformations of matrix theories. We explain how these deformations are related to the TT¯ deformation in two dimensions. In the context of holography, this allows us to view the ten-dimensional near-horizon brane geometry as an intrinsic deformation of the flat non-Lorentzian geometry that arises asymptotically. In field theoretic terms, these generalisations lead to TT¯-like flow equations for the Dp-brane DBI action.

Duality walls, duality trees and fractional branes

In this paper, we compute the NSVZ beta functions for [Formula: see text] four-dimensional quiver theories arising from D-brane probes on singularities, complete with anomalous dimensions, for a large set of phases in the corresponding duality tree. While these beta functions are zero for D-brane probes, they are nonzero in the presence of fractional branes. As a result there is a nontrivial RG behavior. We apply this running of gauge couplings to some toric singularities such as the cones over Hirzebruch and del Pezzo surfaces. We observe the emergence in string theory, of “Duality Walls,” a finite energy scale at which the number of degrees of freedom becomes infinite and beyond which Seiberg duality does not proceed. We also identify certain quiver symmetries as T-duality-like actions in the dual holographic theory.

Vacuum transitions with the Gauss-Bonnet term in D dimensions

In our previous paper [; ], we proposed a probabilistic argument to explain the reason why the cosmological constant is very small in 4D. We can ask a question: if the behavior of tunneling exponent B can be generalized to D-dimension. Moreover, in higher dimensional theory motivated by string theory the Gauss-Bonnet term plays an important role. Therefore, in this paper, we generalize our result in previous paper [; ] to arbitrary D dimensions including the Gauss-Bonnet term. As a result, we have two main results. We find that the Euclidean action of the bounce, B, describing the decay of a de Sitter vacuum, is proportional to k+−(D−2), which has a pole as k+2→0 where k+2 is the curvature of the parent vacuum. This result is similar to the result in 4D. The other result is that we find a new decay channel, describing up-tunneling from anti–de Sitter into de Sitter. The meaning of this new decay channel in the string landscape should be explored in the future. Published by the American Physical Society 2025

Spinning bodies in general relativity from bosonic worldline oscillators

Worldline quantum field theory (WQFT) has proven itself a powerful tool for classical two-body scattering calculations in general relativity. In this paper we develop a new worldline action involving bosonic oscillators, which enables the use of the WQFT formalism to describe massive compact bodies to all orders in their spins. Inspired by bosonic string theory in the tensionless limit, we augment traditional trajectory variables with bosonic oscillators capturing the spin dependence. We show its equivalence to the covariant phase space description of a spinning body in curved space and clarify the role of the spin-supplementary condition in a Hamiltonian treatment. Higher-spin Hamiltonians are classified to linear and quadratic order in curvature. Finally, perturbative computations at 1PM order for arbitrary powers and orientations of spin and at 2PM up to quartic spin order are performed, recovering results from the literature.

A note on background independence in AdS3 string theory

Abstract In this note, we comment on the path integral formulation of string theory on $$ \mathcal{M} $$ M × S3 × $$ {\mathbbm{T}}^4 $$ T 4 where $$ \mathcal{M} $$ M is any hyperbolic 3-manifold. In the special case of k = 1 units of NS-NS flux, we provide a covariant description of the worldsheet theory and argue that the path integral depends only on the details of the conformal boundary $$ \partial \mathcal{M} $$ ∂ M , making the background independence of this theory manifest. We provide a simple path integral argument that the path integral localizes onto holomorphic covering maps from the worldsheet to the boundary. For closed manifolds $$ \mathcal{M} $$ M , the gravitational path integral is argued to be trivial. Finally, we comment on the effect of continuous deformations of the worldsheet theory which introduce non-minimal string tension.

Susy at the FPF

Experimental searches for supersymmetry (SUSY) are entering a new era. The failure to observe signals of sparticle production at the large hadron collider (LHC) has eroded the central motivation for SUSY breaking at the weak scale. However, String Theory requires SUSY at the fundamental scale Ms and hence SUSY could be broken at some high scale below Ms. Actually, if this were the case, the lack of experimental evidence for low-energy SUSY could have been anticipated, because most stringy models with high-scale SUSY breaking predict that sparticles would start popping up above about 10 TeV, well beyond the reach of current LHC experiments. We show that using next generation LHC experiments currently envisioned for the Forward Physics Facility (FPF) we could search for signals of neutrino-modulino oscillations to probe models with string scale in the grand unification region and SUSY breaking driven by sequestered gravity in gauge mediation. This is possible because of the unprecedented flux of neutrinos to be produced as secondary products in LHC collisions during the high-luminosity era and the capability of FPF experiments to detect and identify their flavors.

Testing low energy string theory with strong gravitational lensing by black holes and constraints from EHT observations

Testing low energy string theory with strong gravitational lensing by black holes and constraints from EHT observations

Drinfel’d doubles, twists and all that. in stringy geometry and M theory

Drinfel’d doubles of Lie bialgebroids play an important role in T-duality of string theories. In the presence of H and R fluxes, Lie bialgebroids should be extended to proto Lie bialgebroids. For both cases, the pair is given by two dual vector bundles, and the Drinfel’d double yields a Courant algebroid. However for U-duality, more complicated direct sum decompositions that are not described by dual vector bundles appear. In a previous work, we extended the notion of a Lie bialgebroid for vector bundles that are not necessarily dual. We achieved this by introducing a framework of calculus on algebroids and examining compatibility conditions for various algebroid properties in this framework. Here our aim is two-fold: extending our work on bialgebroids to include both H- and R-twists, and generalizing proto Lie bialgebroids to pairs of arbitrary vector bundles. To this end, we analyze various algebroid axioms and derive twisted compatibility conditions in the presence of twists. We introduce the notion of proto bialgebroids and their Drinfel’d doubles, where the former generalizes both bialgebroids and proto Lie bialgebroids. We also examine the most general form of vector bundle automorphisms of the double, related to twist matrices, that generate a new bracket from a given one. We analyze various examples from both physics and mathematics literatures in our framework.

Susy breaking soft terms in the supersymmetric Pati-Salam landscape from intersecting D6-branes

We investigate the supersymmetry breaking soft terms for all the viable models in the complete landscape of three-family supersymmetric Pati-Salam models arising from intersecting D6-branes on a \U0001d54b6/(ℤ2 × ℤ2) orientifold in type IIA string theory. The calculations are performed in the general scenario of u-moduli dominance with the s-moduli turned on, where the soft terms remain independent of the Yukawa couplings and the Wilson lines. The results for the trilinear coupling, gaugino-masses, squared-mass parameters of squarks, sleptons and Higgs depend on the brane wrapping numbers and the susy breaking parameters. We find that unlike the Yukawa couplings which remain unchanged for the models dual under the exchange of two SU(2) sectors, the corresponding soft term parameters only match for the trilinear coupling and the mass of the gluino. This can be explained by the internal geometry where the Yukawa interactions depend only on the triangular areas of the worldsheet instantons while the soft terms have an additional dependence on the orientation-angles of D6-branes in the three two-tori. In the special limit of parameter space we find universal masses for the Higgs and the gauginos.

Spin cobordism and the gauge group of type I/heterotic string theory

Cobordism offers a unique perspective into the non-perturbative sector of string theory by demanding the absence of higher form global symmetries for quantum gravitational consistency. In this work we compute the spin cobordism groups of the classifying space of Spin(32)/ℤ2 relevant to describing type I/heterotic string theory and explore their (shared) non-perturbative sector. To facilitate this we leverage our knowledge of type I D-brane physics behind the related ko-homology. The computation utilizes several established tools from algebraic topology, the focus here is on two spectral sequences. First, the Eilenberg-Moore spectral sequence is used to obtain the cohomology of the classifying space of the Spin(32)/ℤ2 with ℤ2 coefficients. This will enable us to start the Adams spectral sequence for finally obtaining our result, the spin cobordism groups. We conclude by providing a string theoretic interpretation to the cobordism groups.

On stabilization of magnetically charged brane shell and over-extremality

In string theory, we can geometrically realize a metastable state by wrapping D5-branes and anti D5-branes to a singular manifold. We consider wrapping D3-branes to the internal space in this setup. These D3-branes dissolve into the domain wall, which interpolates true vacua and false vacua, forming a bound state. The remnant of the D3-branes can be seen as a background magnetic field on the domain wall, which appears to an observer in 4D spacetime as a magnetically charged, spherically symmetric shell. This brane shell has finite radii due to the nonlinearity peculiar to string theory, even at the probe level. We demonstrate a new stabilization mechanism of the brane shell in 4D spacetime. We add a general relativity-inspired gravitational correction to the brane shells and investigate the influence on its potential. As a result, the potential value at the horizon will be relatively larger than the potential minimum in parameter regions where the influence of gravity is large, and even non-perturbative instabilities can be removed. Moreover, we show the existence of over-extremal states such that (gQ)2 ≥ G4m2 is satisfied in regions where the magnetic field is sufficiently large. At least in our model, this over-extremal shell cannot be completely stabilized by gravitational correction. This paper also addresses the dilemma between stabilizing and achieving an over-extremal state.

Introduction to string theory

These are lecture notes of the introductory String Theory course held by one of the authors for the master program of Theoretical Physics at Turin University. The world-sheet approach to String Theory is pedagogically introduced in the framework of the bosonic string and of the superstring.

(2, 2p + 1) minimal string and intersection theory I

In view of the recent progress in studying matrix model-2D gravity duality, we reexamine some features of (2, 2p + 1) minimal string. After reviewing both sides of the proposed correspondence in this case, a previously unnoted identification between correlation numbers of tachyon operators in certain domain of parameter space and “p-deformed volumes”, which are certain integral transforms of topological recursion data, is described and clarified. This identification allows us to efficiently study correlation numbers at finite matter central charge. In particular, we obtain an intersection-theoretic formula and the simplest recurrent equations for them, analogous to the ones recently derived for Virasoro minimal string. These formulas might be useful in establishing a more thorough connection between worldsheet and matrix model approaches.

A heterotic Kähler gravity and the distance conjecture

Deformations of the heterotic superpotential give rise to a topological holomorphic theory with similarities to both Kodaira-Spencer gravity and holomorphic Chern-Simons theory. Although the action is cubic, it is only quadratic in the complex structure deformations (the Beltrami differential). Treated separately, for large fluxes, or alternatively at large distances in the background complex structure moduli space, these fields can be integrated out to obtain a new field theory in the remaining fields, which describe the complexified hermitian and gauge degrees of freedom. We investigate properties of this new holomorphic theory, and in particular connections to the swampland distance conjecture in the context of heterotic string theory. In the process, we define a new type of symplectic cohomology theory, where the background complex structure Beltrami differential plays the role of the symplectic form.

Density of states, black holes and the Emergent String Conjecture

We study universal features of the density of one-particle states ρ(E) in weakly coupled theories of gravity at energies above the quantum gravity cutoff Λ, defined as the scale suppressing higher-derivative corrections to the Einstein-Hilbert action. Using thermodynamic properties of black holes, we show that in asymptotically flat spacetimes, certain features of ρ(E) above the black hole threshold Mmin are an indicator for the existence of large extra dimensions, and cannot be reproduced by any lower-dimensional field theory with finitely many fields satisfying the weak energy condition. Based on the properties of gravitational scattering amplitudes, we argue that there needs to exist a (possibly higher-dimensional) effective description of gravity valid up to the cutoff Λ. Combining this with thermodynamic arguments we demonstrate that ρ(E) has to grow exponentially for energies Λ ≪ E ≪ Mmin. Furthermore we show that the tension of any weakly coupled p-brane with p ≥ 1 is bounded from below by Λp+1. We use this to argue that any tower of weakly coupled states with mass below Λ has to be a Kaluza-Klein (KK) tower. Altogether these results indicate that in gravitational weak-coupling limits the lightest tower of states is either a KK tower, or has an exponentially growing degeneracy thereby resembling a string tower. This provides evidence for the Emergent String Conjecture without explicitly relying on string theory or supersymmetry.

Bootstrapping line defects in AdS3/CFT2

We study correlators of insertions along 1/2 BPS line defects in the holographic dual to type IIB string theory in AdS3 × S3 × T4 with mixed Ramond-Ramond and Neveu Schwarz-Neveu Schwarz three-form flux. These defects break the symmetries of the bulk CFT2 as PSU(1, 1|2)2 × SO(4) → PSU(1, 1|2) × SU(2), defining displacement and tilt supermultiplets. We focus on the two-, three- and four-point functions of these supermultiplets, which we compute using analytic conformal bootstrap up to next-to-leading order in their strong-coupling expansion. We obtain a bootstrap result that only depends on two OPE coefficients. We perform a Witten diagram check of the bootstrap result, obtaining an holographic interpretation of the two OPE coefficients that are not constrained by the bootstrap procedure.

Holographic RG flows and Janus interfaces from ISO(3)×U(1) F(4) gauged supergravity

We study six-dimensional F(4) gauged supergravity coupled to four vector multiplets with a non-semisimple ISO(3)×U(1) gauge group. This gauged supergravity arises from a consistent truncation of type IIB string theory on S2×Σ with Σ being a Riemann surface. We find that the gauged supergravity admits two SO(3) symmetric AdS6 vacua, one with N=(1,1) supersymmetry and the other one as non-supersymmetric. We compute all scalar masses at these critical points and find that only the supersymmetric AdS6 vacuum is stable. By truncating to SO(3)×U(1) and SO(2)×U(1) invariant sectors, we study holographic renormalization group flow solutions from this critical point to a number of nonconformal phases of the dual N=2 superconformal field theories in five dimensions. Finally, we give some examples of supersymmetric Janus solutions describing conformal interfaces within the five-dimensional superconformal field theories. All of these solutions provide first holographic results from matter-coupled F(4) gauged supergravity with non-semisimple gauge groups. Published by the American Physical Society 2025

Investigating 9d/8d non-supersymmetric branes and theories from supersymmetric heterotic strings

We consider heterotic string theories in nine and eight dimensions. We identify the disconnected part of the spacetime gauge group by studying the outer automorphism of the charge lattices. The absence of the global symmetry indicates the existence of non-supersymmetric codimension two branes. Moreover, we provide a list of gauge groups and matter contents of non-supersymmetric rank-reduced heterotic string theories (a branch corresponding to the E8 string on S1) from the orbifolding of the outer automorphism as well as the fermion parity. We also provide examples in eight dimensions.

Black hole effective theory for strongly interacting matter

We establish a new tool for studying strongly coupled matter: an effective theory of black holes in gravity, which maps to a hydrodynamic description of field theories via the gauge-gravity duality. Our approach is inspired by previously known effective theories found in the limit of a high number of dimensions. We argue that the new approach can accurately describe phase transitions in a wide class of theories, such as the Yang-Mills and other nearly critical field theories. As an application to a previously unsolved problem, we analyze the interface between confining and deconfining phases in holographic Yang-Mills theory. Published by the American Physical Society 2025