arXiv subjects

George Tringas

Publications and source records attributed to George Tringas.

At least 19 recordsLinked to original sources

arXiv2026

Scale-separated AdS$_2$ flux vacua from type II

Motivated by the question of whether the internal scales of a compactification can be parametrically decoupled from the external curvature scale, and by the possibility of probing such vacua holographically, we construct the first AdS$_2$ flux vacua with parametric scale separation. We compactify type II string theory on a $G_2$ structure orbifold times a circle in the presence of smeared spacetime-filling O1/O5-planes or O4/O8-planes, together with NSNS and RR fluxes. We derive the two-dimensional dilaton-gravity effective theory and exhibit families of vacua in which unbounded $F_5$ and $H_7$ fluxes provide parametric control in type IIB, while unbounded $F_4$, $F_8$, and $H_7$ fluxes provide parametric control in type IIA. For large flux quanta, the string coupling becomes parametrically weak, all internal bulk radii become parametrically large in string units, and the Kaluza--Klein scale separates from the $\mathrm{AdS}_2$ curvature scale. We analyze the ten-dimensional Killing-spinor equations and identify parametric branches preserving $\mathcal N=(1,1)$ supersymmetry in two dimensions. We explain how our geometrically scale-separated AdS$_2$ vacua are compatible with a recent no-go theorem for scale separation in theories with extended supersymmetry. Finally, we discuss various T-dualities leading to other type IIB and type IIA compactifications on $G_2$ structure spaces times a circle and $SU(3)$ structure spaces times a two-torus.

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arXiv2026

$G_2$ flux compactifications

We derive the three-dimensional $\mathcal{N}=1$ effective theories obtained by compactifying all five ten-dimensional string theories on generic seven-dimensional manifolds with $G_2$ structure. The resulting flux compactifications are worked out explicitly, including the full moduli dependence of the scalar potential, kinetic terms, axionic sectors, gauge fields, St\"uckelberg couplings, and the allowed geometric and form-flux data. Our results extend previous analyses by incorporating fields and fluxes that are generically present in $G_2$ reductions, and provide a unified framework for comparing type IIA, type IIB, type I and heterotic compactifications to three dimensions. In particular, the effective theories organize naturally in terms of the real superpotential formulation of three-dimensional $\mathcal{N}=1$ supergravity, making the relation between fluxes, torsion, Chern--Simons data, and moduli potentials manifest.

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arXiv2026

T-dualities and scale-separated AdS$_3$ in massless IIA on $(X_6 \times S^1)/\mathbb{Z}_2$

Motivated by the question of whether scale-separated AdS$_3$ flux vacua arising from G$_2$ compactifications admit an uplift to eleven-dimensional supergravity, we construct scale-separated AdS$_3$ flux vacua in massless type IIA with only O6-planes. We first present new scale-separated solutions in massive type IIA on a G$_2$ holonomy toroidal orbifold with four smeared O6-planes, analyze their properties, and then perform a double T-duality to obtain the corresponding massless backgrounds. In the dual frame, the internal space is locally given by a six-dimensional quotient space $X_6$ with an $\mathrm{SU}(3)$ structure of Iwasawa type times an untwisted circle $S^1$, while globally it is further modded out by a non-trivial $\mathbb{Z}_2$ quotient inherited from the G$_2$ orbifold action. Finally, we use T-duality to derive the corresponding superpotential in massless type IIA and identify parametrically classical, scale-separated families of solutions, as well as a family with parametrically large radii, scale separation, and strong coupling, thus allowing for an uplift to eleven-dimensional supergravity.

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arXiv2026

Holographic Charged Transport with Higher Derivatives

We compute the first-order hydrodynamic transport coefficients (shear viscosity $\eta$, bulk viscosity $\zeta$, and charge conductivity $\sigma$) for a broad class of strongly coupled, four-dimensional charged relativistic gauge theory plasma with holographic gravitational duals containing higher-derivative corrections. The landscape of our holographic models captures non-conformal gauge theories with an arbitrary number of relevant coupling constants and a general scalar potential in the gravitational dual, allowing for a systematic exploration of charged transport along generic holographic RG flows. The leading-order higher-derivative corrections probe gauge theories with non-equal central charges $c\ne a$ at the ultraviolet fixed point, and enable the engineering of diverse temperature and charge density profiles for the viscosities and the conductivity. Our results establish the membrane paradigm in higher-derivative holographic models: all the transport coefficients are extracted from the black brane horizon values of the gravitational scalars, and various functions defining the gravitational holographic dual.

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arXiv2025

Classical scale-separated AdS$_3$ vacua in heterotic string theory

We provide the first scale-separated AdS solutions from compactifications of the heterotic string. Our solutions have parametrically weak coupling, large volume, and the internal KK scale is parametrically smaller than the AdS length. These AdS$_3$ vacua preserve $\mathcal{N}=1$ supersymmetry and arise from compactifications on $G_2$ structure manifolds with $H$ flux and (smeared) gravitational instantons. All geometric moduli are stabilized, fluxes quantized, and the solutions are parametrically controlled in an appropriate large-flux limit.

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arXiv2025

T-dualities and scale-separated AdS$_3$ in type I

We perform three T-dualities on previously found, classical $\mathcal{N}=1$ scale-separated AdS$_3$ solutions of massive type IIA supergravity. These solutions arose from a compactification on a toroidal $G_2$-holonomy space with smeared O2/D2 and O6/D6 sources. The T-dual backgrounds are classical $\mathcal{N}=1$ AdS$_3$ solutions of type IIB supergravity with O5/D5 and O9/D9 sources (type I) compactified on a space with $G_2$-structure and non-vanishing Ricci scalar. We generalize the original solutions in IIA in the T-dual picture and present on the type IIB side fully classical solutions with parametric control, scale separation, and integer conformal dimensions for the dual operators in the corresponding CFT. We also obtain strongly coupled solutions with the same properties. These are S-dual to parametrically controlled classical solutions of the heterotic SO(32) string theory.

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arXiv2025

Warped G$_2$-throats in IIA and uplift dSillusions

Flux compactifications of IIA supergravity on orientifolded G$_2$-manifolds have been argued to allow for classical Minkowski$_3$ vacua with moduli and scale-separated AdS$_3$ vacua with full moduli stabilisation. To further uplift these vacua to meta-stable dS$_3$ vacua using anti-D2 branes, warped throats are desirable. We study the flux-stabilisation of local "CGLP-type" throats in compact G$_2$ spaces, and discuss consistency constraints on anti-brane uplifting. Despite the classical AdS$_3$ vacua to be free of tachyons, we find that uplifting from anti-branes down warped throats is forbidden. If instead we rely on hypothetical AdS$_3$ vacua that arise from quantum corrections to the classical Minkowski$_3$ vacua, we find that (similarly to the 4d analogues) consistency constraints point in opposite directions. However, there is potentially an advantage over 4d when it comes to concrete fine-tuning freedom of numbers, such as tadpole constraints.

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arXiv2025

Scale separation from O-planes

Orientifold planes play a crucial role in flux compactifications of string theory, and we demonstrate their deep connection to achieving scale-separated solutions. Specifically, we show that when an orientifold plane contributes at leading order to the non-zero value of the scalar potential, then either the weak coupling limit or the large volume limit implies scale separation, meaning that the Kaluza-Klein tower mass decouples from the inverse length scale of the lower-dimensional theory. Notably, in the supergravity limit such solutions are inherently scale-separated. This result is independent of the spacetime dimension and the dimensionality of the O$p$-plane as long as $p<7$. Similarly, we show, extending previous results, that parametric scale separation is not possible for isotropic compactifications with a leading curvature term that generically arise in the AdS/CFT context. We classify all possible flux compactification setups in both type IIA and type IIB string theory for O$p$-planes with $2\leq p\leq 6$ and present their universal features. While the parametrically controlled scale-separated solutions are all AdS, we also find setups that allow for dS vacua. We prove that flux quantization prevents these dS vacua in isotropic compactifications from arising in a regime of parametric control.

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arXiv2025

Integer dual dimensions in scale-separated AdS$_3$ from massive IIA

We study supersymmetric scale-separated AdS$_3$ flux vacua of massive IIA on G2 orbifolds with smeared orientifold planes. We consider two types of $T^7/Z_2^3$ orbifolds which, with appropriate flux choices, yield integer dual dimensions for the operators corresponding to the closed string scalar fields in the dual CFT. As with all other known examples, the dual conformal dimensions are only parametrically close to integer values.

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arXiv2025

Single versus multifield scalar potentials from string theory

In this work, we investigate the properties of string effective theories with scalar field(s) and a scalar potential. We first claim that in most examples known, such theories are multifield, with at least 2 non-compact field directions; the few counter-examples appear to be very specific and isolated. Such a systematic multifield situation has important implications for cosmology. Characterising properties of the scalar potential $V$ is also more delicate in a multifield setting. We provide several examples of string effective theories with $V>0$, where the latter admits an asymptotically flat direction along an off-shell field trajectory: in other words, there exists a limit $\varphi \rightarrow \infty$ for which $\frac{|\partial_{\varphi} V|}{V} \rightarrow 0$. It is thus meaningless to look for a lower bound to this single field quantity in a multifield setting; the complete gradient $\nabla V$ is then better suited. Restricting to on-shell trajectories, this question remains open, especially when following the steepest descent or more generally a gradient flow evolution. Interestingly, single field statements in multifield theories seem less problematic for $V<0$.

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arXiv2023

On/off scale separation

We discuss minimally supersymmetric AdS$_3$ flux vacua of massive type IIA supergravity on G2-orientifolds. We find that configurations that are scale-separated can be within finite distance from non scale-separated ones, while both remain at large volume, weak coupling and have moduli stabilization. The transition is achieved with the use of a D4-brane modulus, which allows the $F_4$ flux to jump, and has an effective potential always accessible to the three-dimensional low-energy theory. Our analysis further allows us to check the distance conjecture quantitatively, as we can track explicitly the masses of the KK modes.

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arXiv2023

Extensions of a scale-separated AdS$_4$ solution and their mass spectrum

We consider two extensions of the so-called DGKT solution, a 4d scale-separated anti-de Sitter (AdS) solution obtained as a compactification on a 6d torus orbifold. Each extension consists in a specific large $n$ expansion beyond the DGKT solution, where $n$ is the unbounded $F_4$-flux parameter. One of the extensions considered generalizes the known warped, partially backreacted solution. We analyse the two extensions in 10d massive type IIA supergravity as well as in a 4d effective theory, using a general warped compactification formalism, including axions. On top of known corrections to DGKT, we mainly get new ones from $F_4$; other fluxes are very constrained by flux quantization. In each extension, one would expect corresponding corrections to the mass spectrum, before reaching contributions from $\alpha'$-corrections. But the mass spectrum turns out to be robust, and conformal dimensions remain unchanged.

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arXiv2023

Anisotropic scale-separated AdS$_4$ flux vacua

We present minimally supersymmetric AdS$_4$ flux vacua derived from massive type IIA compactified on $T^6/\mathbb{Z}_3\times \mathbb{Z}_3$ orbifold, characterized by unconstrained fluxes with general scaling. We discover anisotropic scaling solutions where scale separation is realized in the supergravity limit and the subvolumes of the internal space become large and anisotropic for large values of unconstrained fluxes. Additionally, we identify regimes where subvolumes are either shrinking or remain constant while scale separation is either broken or realized. Then we employ a probe anti-D4-brane to interpolate between vacua, finding that it interpolates through the regimes we previously identified. Finally, we utilize an open string modulus of the anti-D4-brane to calculate the distance between vacua for the regime where scale separation is realized in the supergravity limit. We show the dependence of both the geodesic distance and the distance conjecture parameter on the flux scaling.

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arXiv2023

The Weak Gravity Conjecture, Overcharged Shells and Gravitational Traps

The Weak Gravity Conjecture predicts that in quantum gravity there should exist overcharged states, that is states with charge larger than their mass. Extending this to large masses and charges, we are expecting similar overcharged classical solutions. This has been demonstrated in higher-derivative extensions of General Relativity. In this paper we investigate the existence of overcharged solutions in General Relativity. We study the dynamics of a thin shell of mass $m$ and charge $Q$ under the action of its own gravitational and $U(1)$ fields. We show that shells with surface energy $σ$ and pressure $P$ obeying $P=wσ$ with $0\leq w\leq 1$ are necessarily undercharged $m\geq |Q|$ and always collapse to form Reissner-Nordström black holes. Nevertheless, if $-1\leq w<0$, we find that overcharged $m\leq |Q|$ shells exist, which however, are inevitably stabilized at finite radial distance.

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arXiv2023

Negative scalar potentials and the swampland: an Anti-Trans-Planckian Censorship Conjecture

In this paper, we derive a characterisation of negative scalar potentials, $V<0$, in $d$-dimensional effective theories of quantum gravity. This is achieved thanks to an Anti-Trans-Planckian Censorship Conjecture (ATCC), inspired by a refined version of the TCC. The ATCC relies on the fact that in a contracting universe, modes that become sub-Planckian in length violate the validity of the effective theory. In the asymptotics of field space, we deduce that $-V'/V \geq c_0$ when $V' \geq 0$. The rate $c_0 = 2/\sqrt{(d-1)(d-2)}$ is successfully tested in several string compactifications for $d\geq 4$. In addition, a new asymptotic condition, $V''/V \geq c_0^2$, is derived. By extrapolation to anti-de Sitter solutions of radius $l$, we infer the existence of a scalar whose mass should obey $m^2 l^2 \lesssim -2$. This property is verified in many supersymmetric examples.

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arXiv2022

O6-plane backreaction on scale-separated Type IIA AdS$_3$ vacua

We evaluate the backreaction of O6-planes in scale-separated $\text{AdS}_3$ flux vacua of massive Type IIA. Using the appropriate flux scaling we show that the corrections to the various background fields and moduli are controlled and subleading when going from smeared to localized sources. Similarly, the backreaction corrections to the scalar potential are parametrically small in the scale-separation limit, assuming always that the near-O6-plane singularities will find a resolution within string theory, even in the presence of a Romans mass. Our analysis is based on the equations of motion and therefore applies also to the non-supersymmetric vacua.

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arXiv2021

On the Vacuum Structure of the $\mathcal{N}=4$ Conformal Supergravity

We consider ${\cal N}=4$ conformal supergravity with an arbitrary holomorphic function of the complex scalar $S$ which parametrizes the $SU(1,1)/U(1)$ coset. Assuming non-vanishings vevs for $S$ and the scalars in a symmetric matrix $E_{ij}$ of the $\overline{\bf 10}$ of $SU(4)$ R-symmetry group, we determine the vacuum structure of the theory. We find that the possible vacua are classified by the number of zero eigenvalues of the scalar matrix and the spacetime is either Minkowski, de Sitter or anti-de Sitter. We determine the spectrum of the scalar fluctuations and we find that it contains tachyonic states which however can be removed by appropriate choice of the unspecified at the supergravity level holomorphic function. Finally, we also establish that $S$-supersymmetry is always broken whereas $Q$-supersymmetry exists only on flat Minkowski spacetime.

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arXiv2021

Three-dimensional flux vacua from IIB on co-calibrated G2 orientifolds

We derive the 3D N=1 superpotential for the closed string sector of type IIB supergravity on toroidal O5 orientifolds with co-calibrated G2 structure and RR background flux. We find that such compactifications can provide full closed string moduli stabilization on supersymmetric AdS$_3$ vacua, and once we include brane-supersymmetry-breaking we also find indication for the existence of classical 3D de Sitter solutions. The latter however are rather difficult to reconcile with the shape moduli stabilization and flux quantization. We also discuss the possibility of achieving scale separation in AdS$_3$ and dS$_3$ vacua, but such effects seems to be hindered by the geometric flux quantization.

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