Taking horizonless black hole mimickers out for a spin

In this paper, we study rotating horizon less black shells as an alternative to Kerr black holes. We make use of Ernst's potential to solve the Einstein equations perturbatively in the angular momentum $a$. Calculating to order $a^6$, we find accurate predictions up to about $a=0.45$, where the quadrupole moment is predicted to be around $1\%$ higher than its Kerr value; higher multipole moments show deviation of the order of $\sim 10\%$. Our analysis takes into account deformations of the black shells, and we propose that it can be used for numerical simulations comparing gravitational waves emitted by orbiting black shells with those emitted by orbiting black holes. In our analysis, we make extensive use of relativistic hydrodynamics, and discover an intricate structure of circulating flows of fluid and heat on the black shell, sustained by the Unruh effect.Comment: A Wolfram Mathematica notebook that contains the results obtained in this paper, and further results to order $a^6$, is included with the submission. No external packages are used in the noteboo

Hierarchies of RG flows in 6d (1,0)(1,0) massive E-strings

We extend the analysis of arXiv:2208.11703 to the 6d $(1,0)$ SCFTs known as massive E-string theories, which can be engineered in massive Type IIA with $8-n_0<8$ D8-branes close to an O8$^-$ (or O8$^*$ if $n_0=8,9$). For each choice of $n_0=1,\ldots,9$ the massive $E_{1+(8-n_0)}$-strings (including the more exotic $\tilde{E}_1$ and $E_0$) are classified by constrained $E_8$ Kac labels, i.e. a subset of $\text{Hom}(\mathbb{Z}_k,E_8)$, from which one can read off the flavor subalgebra of $E_{1+(8-n_0)}$ of each SCFT. We construct hierarchies for two types of Higgs branch RG flows: flows between massive theories defined by the same $n_0$ but different labels; flows between massive theories with different $n_0$. These latter flows are triggered by T-brane vev's for the right $\mathrm{SU}$ factor of the SCFT global symmetry, whose rank is a function of both $k$ and $n_0$, a situation which has so far remained vastly unexplored.Comment: Part II of a series of papers; 37+11 pages; 13 figure

Dark Bubble: FAQs. Misconceptions, and why it is not Randall-Sundrum

In this paper we clear up misconceptions concerning the dark bubble model as a realization of dark energy in string theory. In particular we point out important differences with Randall-Sundrum, and explain why gravity neither is, nor need to be, localized on the dark bubble

The Higgs branch of heterotic ALE instantons

We begin a study the Higgs branches of the six-dimensional (1,0) little string theories (LSTs) governing the worldvolumes of heterotic ALE instantons. We give a description of such spaces by constructing the corresponding \textit{magnetic quivers}. The latter are three-dimensional $\mathcal{N}=4$ quiver gauge theories that flow in the infrared to 3d fixed points whose quantum corrected Coulomb branches are the Higgs branches of the six-dimensional theories of interest. We present results for both types of Heterotic strings, and mostly for $\mathbb C^2/\mathbb Z_k$ ALE spaces. Our analysis is valid both in the absence and in the presence of small instantons. Along the way, we also describe small $SO(32)$ instanton transitions in terms of the corresponding magnetic quivers, which parallels a similar treatment of the small instanton transitions in the context of the $E_8\times E_8$ heterotic string.tiComment: 44 pages, 3 figure

A new vista on the Heterotic Moduli Space from Six and Three Dimensions

We settle a long-standing question about the hypermultiplet moduli spaces of the heterotic strings on ALE singularities. These heterotic backgrounds are specified by the singularity type, an instanton number, and a (nontrivial) flat connection at infinity. Building on their interpretation as six-dimensional theories, we determine a class of three-dimensional $\mathcal{N}=4$ quiver gauge theories whose quantum corrected Coulomb branch coincides with the exact heterotic hypermultiplet moduli space.Comment: 6 page

Shedding light on dark bubble cosmology

Dark bubble cosmology is an alternative paradigm to compactification, which can circumvent issues of moduli stabilization and scale separation. In this paper we investigate how electromagnetic fields can be incorporated in this framework. Worldvolume fields backreact on the ambient universe in which the bubble expands, which in turn affects the energy-momentum distribution and the effective gravity induced on the brane. We compute these effects, showing that the resulting four-dimensional cosmology consistently includes electromagnetic waves.Comment: 21 pages, 1 figur

Prognostic implications of glycated hemoglobin in nondiabetic patients with acute coronary syndrome

Background: In nondiabetic patients with acute coronary syndrome, acute hyperglycemia is associated with adverse outcome. Whether this association is due merely to hyperglycemia as an acute stress response or whether longer-term glycometabolic derangements are also involved is uncertain. It was our aim to determine the association between chronic hyperglycemia (hemoglobin A1c (HbA1c) and outcome in nondiabetic patients with acute coronary syndrome.Methods: This observational study included consecutive patients (n=47) without known diabetes mellitus admitted with acute coronary syndrome (STEMI, NSTEMI, UA). HbA1c was measured on admission. The main outcome was MACE (major adverse cardiac events including death, cardiogenic shock, arrhythmia, heart failure). The patients were divided into 2 groups according to their HbA1c level (group 1 HbA1c5.7%).Results: There was no significant difference between baseline characteristics of both groups but complications were seen in higher number cases with HbA1c >5.7%. No significant difference in mortality was found. On multivariate logistic regression analysis HbA1c >5.7% was found to be an independent predictor of MACE.Conclusions: There was no significant difference between baseline characteristics of both groups but complications were seen in higher number cases with HbA1c>5.7%. No significant difference in mortality was found. On multivariate logistic regression analysis HbA1c>5.7% was found to be an independent predictor of MACE.

New horizons in string theory : bubble babble in search of darkness

It was discovered nearly two decades ago that we live in an accelerating universe that is dominated by dark energy. Understanding the origin of such an energy has turned out to be a very difficult open question in physics, and calls on the need for a fundamental theory like string theory. However, despite decades-long effort, string theory has proven incredibly resilient to a satisfactory construction of dark energy within its framework. In the first part of this thesis and the included papers, we examine this problem and propose two possible solutions. The first is a construction within the framework of M-theory, the eleven dimensional cousin of string theory. Using only well-understood geometric ingredients and higher-derivative corrections to eleven dimensional supergravity, we present a new class of four dimensional vacua that contain dark energy. In the process, we also construct a new class of non-supersymmetric Minkowski vacua that were previously not known. Our second idea is a novel proposal that our universe could be embedded on the surface of an enormous spherical bubble that is expanding in a five dimensional anti de Sitter spacetime. The bubble is made of branes in string theory and its expansion is driven by the difference in the cosmological constants across it. We argued that such a construction arises naturally in string theory, and showed how four dimensional gravity arises in such a universe. We further showed that four dimensional matter and radiation arise from quantities that are innately five dimensional. Another challenging problem in physics concerns the nature of black holes – the presence of an event horizon in particular. This poses a paradox between well understood physical principles, and requires a fundamental theory for its resolution. Towards this goal, we constructed a novel class of horizonless objects that mimics black holes, and proposed these objects as an alternative end point of gravitational collapse. Subsequently, we constructed slowly rotating versions of these "black shells" and proposed an observational signature that could distinguish them from black holes in cosmological experiments. This is discussed in the second part of the thesis and in the included papers