E-Thesis 539 views 173 downloads
Non-perturbative aspects of gauge theories from gauge-gravity dualities / JOHN ROUGHLEY
Swansea University Author: JOHN ROUGHLEY
DOI (Published version): 10.23889/SUthesis.58266
Abstract
In this Ph.D. Thesis we consider two speci˝c supergravities which are well-established within the literature on holography, and which are known to provide the low-energy e˙ective description of either superstring theory or M-theory: the six-dimensional half-maximal theory of Romans, and the maximal...
| Published: |
Swansea
2021
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| Institution: | Swansea University |
| Degree level: | Doctoral |
| Degree name: | Ph.D |
| Supervisor: | Piai, Maurizio ; Lucini, Biagio |
| URI: | https://cronfa.swan.ac.uk/Record/cronfa58266 |
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| Abstract: |
In this Ph.D. Thesis we consider two speci˝c supergravities which are well-established within the literature on holography, and which are known to provide the low-energy e˙ective description of either superstring theory or M-theory: the six-dimensional half-maximal theory of Romans, and the maximal supergravity in seven dimensions.We implement their dimensional reduction by compactifying on an S1 and T 2, respectively, to obtain a ˝ve-dimensional sigma-model coupled to grav-ity. Spectra of bosonic excitations are computed numerically by considering ˝eld ˛uctuations on background geometries which holographically realise con-˝nement. We furthermore propose a diagnostic tool to detect mixing e˙ects between scalar resonances and the pseudo-NambuGoldstone boson associated with spontaneous breaking of conformal invariance: the dilaton. This test con-sists of neglecting a certain component of the spin-0 ˛uctuation variables, ef-fectively disregarding their back-reaction on the underlying geometry; where discrepancies arise compared to the complete calculation we infer dilaton mix-ing. For both theories this analysis evinces a parametrically light dilaton.For each supergravity we uncover a tachyonic instability within their param-eter space; motivated by these pathological ˝ndings we proceed to conduct an investigation into their respective phase structures, reasoning that there must necessarily exist some mechanism by which these instabilities are rendered phys-ically inaccessible. We compile a comprehensive catalogue of geometrically dis-tinct backgrounds admissible within each theory, and derive general expressionsfor their holographically renormalised free energy F. Another numerical rou-tine is employed to systematically extract data for some special deformationparameters, and F is plotted in units of an appropriate universal scale.Our analysis proves fruitful: each theory exhibits clear evidence of a ˝rst-order phase transition which induces the spontaneous decompacti˝cation of the shrinking circular dimension before the instability manifests, favouring instead a class of singular solutions. The aforementioned dilaton resonance appears only along a metastable portion of the branch of con˝ning backgrounds. |
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| Item Description: |
ORCiD identifier https://orcid.org/0000-0001-7299-6781 |
| Keywords: |
Gauge/gravity duality; Holography; Supergravity |
| College: |
Faculty of Science and Engineering |