arXiv subjects

Eoin Ó Colgáin

Publications and source records attributed to Eoin Ó Colgáin.

At least 55 records · Page 3Linked to original sources

arXiv2020

Cosmology Intertwined II: The Hubble Constant Tension

The current cosmological probes have provided a fantastic confirmation of the standard $Λ$ Cold Dark Matter cosmological model, that has been constrained with unprecedented accuracy. However, with the increase of the experimental sensitivity a few statistically significant tensions between different independent cosmological datasets emerged. While these tensions can be in portion the result of systematic errors, the persistence after several years of accurate analysis strongly hints at cracks in the standard cosmological scenario and the need for new physics. In this Letter of Interest we will focus on the $4.4σ$ tension between the Planck estimate of the Hubble constant $H_0$ and the SH0ES collaboration measurements. After showing the $H_0$ evaluations made from different teams using different methods and geometric calibrations, we will list a few interesting new physics models that could solve this tension and discuss how the next decade experiments will be crucial.

astro-ph.CO↗

arXiv2020

Cosmology Intertwined I: Perspectives for the Next Decade

The standard $Λ$ Cold Dark Matter cosmological model provides an amazing description of a wide range of astrophysical and astronomical data. However, there are a few big open questions, that make the standard model look like a first-order approximation to a more realistic scenario that still needs to be fully understood. In this Letter of Interest we will list a few important goals that need to be addressed in the next decade, also taking into account the current discordances present between the different cosmological probes, as the Hubble constant $H_0$ value, the $σ_8 - S_8$ tension, and the anomalies present in the Planck results. Finally, we will give an overview of upgraded experiments and next-generation space-missions and facilities on Earth, that will be of crucial importance to address all these questions.

astro-ph.CO↗

arXiv2020

Cosmology Intertwined IV: The Age of the Universe and its Curvature

A precise measurement of the curvature of the Universe is of primeval importance for cosmology since it could not only confirm the paradigm of primordial inflation but also help in discriminating between different early Universe scenarios. The recent observations, while broadly consistent with a spatially flat standard $Λ$ Cold Dark Matter ($Λ$CDM) model, are showing tensions that still allow (and, in some cases, even suggest) a few percent deviations from a flat universe. In particular, the Planck Cosmic Microwave Background power spectra, assuming the nominal likelihood, prefer a closed universe at more than 99\% confidence level. While new physics could be in action, this anomaly may be the result of an unresolved systematic error or just a statistical fluctuation. However, since a positive curvature allows a larger age of the Universe, an accurate determination of the age of the oldest objects provides a smoking gun in confirming or falsifying the current flat $Λ$CDM model.

astro-ph.CO↗

arXiv2019

Testing the Swampland: $H_0$ tension

The de Sitter Swampland conjecture compels us to consider dark energy models where $λ(ϕ) \equiv |\nabla_ϕ V|/V$ is bounded below by a positive constant. Moreover, it has been argued for Quintessence models that the constant $λ$ scenario is the least constrained. Here we demonstrate that increasing $λ$ only exacerbates existing tension in the Hubble constant $H_0$. The identification of dark energy models that both evade observational bounds and alleviate $H_0$ tension constitutes a robust test for the Swampland program.

astro-ph.CO↗

arXiv2019

A hint of matter underdensity at low $z$?

The $Λ$CDM cosmological model provides to first approximation a good description of the universe, but various tensions with data, most notably Hubble tension, persist. In this work we confront $Λ$CDM with the Pantheon Type Ia supernovae dataset and perform a two-parameter fit of the distance modulus for a running cut-off $z_{\textrm{max}}$. We observe that in a window between $z_{\textrm{max}} \approx 0.1$ and $z_{\textrm{max}} \approx 0.16$ there is a 1 - 2 $σ$ discrepancy with the Planck value $ω_m = 0.315 \pm 0.007$, which points to a potential matter underdensity. For high-energy theorists, the analysis appears to support the de Sitter Swampland conjecture.

astro-ph.CO↗

arXiv2019

Tri-vector deformations in $d=11$ supergravity

We construct a $d=11$ supergravity analogue of the open-closed string map in the context of SL(5) Exceptional Field Theory (ExFT). The deformation parameter tri-vector $Ω$ generalizes the non-commutativity bi-vector parameter $Θ$ of the open string. When applied to solutions in $d=11$, this map provides an economical way of performing TsT deformations, and may be used to recover $d=10$ Yang-Baxter deformations after dimensional reduction. We present a generalization of the Classical Yang-Baxter Equation (CYBE) for rank 3 objects, which emerges from $d=11$ supergravity and the SL(5) ExFT. This equation is shown to reduce to the $d=10$ CYBE upon dimensional reduction.

hep-th↗

arXiv2019

de Sitter Swampland, $H_0$ tension & observation

Realising de Sitter vacua in string theory is challenging. For this reason it has been conjectured that de Sitter vacua inhabit the Swampland of inconsistent low-energy effective theories coupled to gravity. Since de Sitter is an attractor for $Λ$CDM, the conjecture calls $Λ$CDM into question. Reality appears sympathetic to this idea as local measurements of the Hubble constant $H_0$ are also at odds with $Λ$CDM analysis of Planck data. This tension suggests that the de Sitter state is unstable, thereby implying a turning point in the Hubble parameter. We present a model relieving this tension, which predicts a turning at small positive redshift $z_*$ that is dictated by present-day matter density $ω_m$. This feature is easily identified by homogeneous surveys covering redshifts $z \leq 0.1$. We comment on the implications for the Swampland program.

hep-th↗

arXiv2019

Holographic integration of $T \bar{T}$ and $J \bar{T}$ via $O(d,d)$

Prompted by the recent developments in integrable single trace $T \bar{T}$ and $J \bar{T}$ deformations of 2d CFTs, we analyse such deformations in the context of $AdS_3/CFT_2$ from the dual string worldsheet CFT viewpoint. We observe that the finite form of these deformations can be recast as $O(d,d)$ transformations, which are an integrated form of the corresponding Exactly Marginal Deformations (EMD) in the worldsheet Wess-Zumino-Witten (WZW) model, thereby generalising the Yang-Baxter class that includes TsT. Furthermore, the equivalence between $O(d,d)$ transformations and marginal deformations of WZW models, proposed by Hassan and Sen for Abelian chiral currents, can be extended to non-Abelian chiral currents to recover a well-known constraint on EMD in the worldsheet CFT. We also argue that such EMD are also solvable from the worldsheet theory viewpoint.

hep-th↗

arXiv2018

Embedding the modified CYBE in Supergravity

It has recently been demonstrated that the Classical Yang-Baxter Equation (CYBE) emerges from supergravity via the open-closed string map. Thus, given any solution with an isometry group, there exists a deformed solution based on an $r$-matrix solution to the homogeneous CYBE. In this work, we argue that the CYBE emerges exclusively from the NS sector, while the RR sector acts largely as a spectator that supports the spacetimes. Moreover, shifting the dilaton by a constant, one can incorporate $r$-matrix solutions to the modified CYBE, but only for original geometries that are a direct-product of coset spaces. We illustrate our solution generating technique with deformations of $AdS_3 \times S^3 \times M_4$, where $M_4 = T^4$ (K3) and $S^3 \times S^1$, and explicitly construct one and two-parameter (integrable) q-deformations that are solutions to generalised supergravity.

hep-th↗

arXiv2018

Conformal Twists, Yang-Baxter $σ$-models & Holographic Noncommutativity

Expanding upon earlier results [arXiv:1702.02861], we present a compendium of $σ$-models associated with integrable deformations of AdS$_5$ generated by solutions to homogenous classical Yang-Baxter equation. Each example we study from four viewpoints: conformal (Drinfeld) twists, closed string gravity backgrounds, open string parameters and proposed dual noncommutative (NC) gauge theory. Irrespective of whether the deformed background is a solution to supergravity or generalized supergravity, we show that the open string metric associated with each gravity background is undeformed AdS$_5$ with constant open string coupling and the NC structure $Θ$ is directly related to the conformal twist. One novel feature is that $Θ$ exhibits "holographic noncommutativity": while it may exhibit non-trivial dependence on the holographic direction, its value everywhere in the bulk is uniquely determined by its value at the boundary, thus facilitating introduction of a dual NC gauge theory. We show that the divergence of the NC structure $Θ$ is directly related to the unimodularity of the twist. We discuss the implementation of an outer automorphism of the conformal algebra as a coordinate transformation in the AdS bulk and discuss its implications for Yang-Baxter $σ$-models and self-T-duality based on fermionic T-duality. Finally, we comment on implications of our results for the integrability of associated open strings and planar integrability of dual NC gauge theories.

hep-th↗

arXiv2018

On non-Abelian T-duality for non-semisimple groups

We revisit non-Abelian T-duality for non-semisimple groups, where it is well-known that a mixed gravitational-gauge anomaly leads to $σ$-models that are scale, but not Weyl-invariant. Taking into account the variation of a non-local anomalous term in the T-dual $σ$-model of Elitzer, Giveon, Rabinovici, Schwimmer \& Veneziano, we show that the equations of motion of generalized supergravity follow from the $σ$-model once the Killing vector $I$ is identified with the trace of the structure constants. As a result, non-Abelian T-duals with respect to non-semisimple groups are solutions to generalized supergravity. We illustrate our findings with Bianchi spacetimes.

hep-th↗

arXiv2017

Penrose limits and spin chains in the GJV/CS-SYM duality

We examine Penrose limits of the duality proposed by Guarino, Jafferis and Varela between a type IIA massive background of the type of a warped, squashed $AdS_4\times S^6$, and a 2+1 dimensional IR fixed point of ${\cal N}=8$ super Yang-Mills deformed by Chern-Simons terms to ${\cal N}=2$ supersymmetry. One type of Penrose limit for closed strings corresponds to a large charge closed spin chain, and another, for open strings on giant graviton D-branes, corresponds to an open spin chain on sub-determinant operators. For the first limit, we find that like in the ABJM case, there are functions $f_a(λ)$ that interpolate between the perturbative and nonperturbative (string) regions for the magnon energy. For the second, we are unable to match the gravity result with the expected field theory result, making this model more interesting than ones with more supersymmetry.

hep-th↗

arXiv2017

Yang-Baxter $σ$-models, conformal twists, and noncommutative Yang-Mills theory

The Yang-Baxter $σ$-model is a systematic way to generate integrable deformations of AdS$_5\times$S$^5$. We recast the deformations as seen by open strings, where the metric is undeformed AdS$_5\times$S$^5$ with constant string coupling, and all information about the deformation is encoded in the noncommutative (NC) parameter $Θ$. We identify the deformations of AdS$_5$ as twists of the conformal algebra, thus explaining the noncommutativity. We show that the unimodularity conditon on $r$-matrices for supergravity solutions translates into $Θ$ being divergence-free. Integrability of the $σ$-model for unimodular $r$-matrices implies the existence and planar integrability of the dual NC gauge theory.

hep-th↗

arXiv2016

Supersymmetry and non-Abelian T-duality in type II supergravity

We study the effect of T-duality on supersymmetry in the context of type II supergravity. For both U(1) Abelian and SU(2) non-Abelian T-duality, we demonstrate that the supersymmetry variations after T-duality are related to the variations before T-duality through the Kosmann spinorial Lie derivative, which vanishes when the Killing spinors are independent of the T-duality directions. As a byproduct of our analysis, we present closed expressions for SU(2) T-duality in a class of spacetimes with diagonal Bianchi IX symmetry and comment on specific examples of T-dual geometries, including a novel AdS3 geometry with large N = (0,4) superconformal symmetry.

hep-th↗

arXiv2016

Large superconformal near-horizons from M-theory

We report on a classification of supersymmetric solutions to 11D supergravity with $SO(2,2) \times SO(3)$ isometry, which are AdS/CFT dual to 2D CFTs with $\mathcal{N} = (0,4)$ supersymmetry. We recover the Maldacena, Strominger, Witten (MSW) near-horizon with small superconformal symmetry and identify a class of $AdS_3 \times S^2 \times S^2 \times CY_2$ geometries with emergent large superconformal symmetry. This exhausts known compact geometries. Compactification of M-theory on $CY_2$ results in a vacuum of 7D supergravity with large superconformal symmetry, providing a candidate near-horizon for an extremal black hole and a potential new setting to address microstates.

hep-th↗

arXiv2016

3D supergravity from wrapped M5-branes

Through consistent Kaluza-Klein reduction, we construct 3D $\mathcal{N} =2$ gauged supergravities corresponding to twisted compactifications of M5-branes on a product of constant curvature Riemann surfaces, including Kähler-Einstein four-manifolds. We extend the reduction to fermionic supersymmetry variations in order to determine the 3D Killing spinor equations and classify all timelike supersymmetric solutions. As a by-product, we identify an infinite class of new supersymmetric warped $AdS_3$ (Gödel) and warped $d S_3$ solutions. Moreover, we show that the superpotential $T$ encodes the central charge and R symmetry of the dual $\mathcal{N} = (0,2)$ SCFTs in the large $N$ limit. We demonstrate that the R symmetry matches the canonical $U(1)$ isometry from existing classifications of supersymmetric $AdS_3$ solutions to 11D supergravity with $\mathcal{N} = (0,2)$ supersymmetry.

hep-th↗

arXiv2015

All supersymmetric solutions of 3D U(1)$^3$ gauged supergravity

D3-branes wrapping constant curvature Riemann surfaces give rise to 2D N = (0,2) SCFTs, where the superconformal fixed-points are mapped to vacua of 3D N =2 U(1)^3 gauged supergravity. In this work we determine the fermionic supersymmetry variations of the theory and present all supersymmetric solutions. For spacetimes with a timelike Killing vector, we identify new timelike warped AdS_3 (Gödel) and timelike warped dS_3 critical points. We outline the construction of numerical solutions interpolating between fixed-points, demonstrate that these flows are driven by an irrelevant scalar operator in the SCFT and identify the inverse of the superpotential as a candidate c-function. We further classify all spacetimes with a null Killing vector, in the process producing loci in parameter space where null-warped AdS_3 vacua with Schrodinger z=2 symmetry exist. We construct non-supersymmetric spacelike warped AdS_3 geometries based on D3-branes.

hep-th↗

arXiv2015

New $AdS_3 \times S^2$ T-duals with $\mathcal{N} = (0,4)$ supersymmetry

It is well known that Hopf-fibre T-duality and uplift takes the D1-D5 near-horizon into a class of $AdS_3 \times S^2$ geometries in 11D where the internal space is a Calabi-Yau three-fold. Moreover, supersymmetry dictates that Calabi-Yau is the only permissible $SU(3)$-structure manifold. Generalising this duality chain to non-Abelian isometries, a strong parallel exists, resulting in the first explicit example of a class of $AdS_3 \times S^2$ geometries with $SU(2)$-structure. Furthermore, the non-Abelian T-dual of $AdS_3 \times S^3 \times S^3 \times S^1$ results in a new supersymmetric $AdS_3 \times S^2$ geometry, which falls outside of all known classifications. We explore the basic properties of the holographic duals associated to the new backgrounds. We compute the central charges and show that they are compatible with a large $\mathcal{N}=4$ superconformal algebra in the infra-red.

hep-th↗