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Sean Stotyn

Publications and source records attributed to Sean Stotyn.

14 recordsLinked to original sources
arXiv2018

Quasilocal Smarr relation for an asymptotically flat spacetime

We investigate the thermodynamics of Einstein-Maxwell(-Dilaton) theory for an asymptotically flat spacetime in a quasilocal frame. We firstly define a quasilocal thermodynamic potential via the Euclidean on-shell action and formulate a quasilocal Smarr relation from Eulerian theorem. Then we calculate quasilocal energy and surface pressure by employing Brown-York quasilocal method along with Mann-Marolf counterterm and find entropy from the quasilocal thermodynamic potential. These quasilocal variables are consistent with Tolman temperature and the entropy in a quasilocal frame turns out to be same as the Bekenstein-Hawking entropy. As a result, we found that a surface pressure term and its conjugate variable, a quasilocal area, do not participate in a quasilocal thermodynamic potential, but should present in a quasilocal Smarr relation and the quasilocal first law of black hole thermodynamics. For dyonic black hole solutions having dynamic dilaton field, non-trivial dilaton contribution should take part in the quasilocal first law but not in the quasilocal Smarr relation.

hep-th↗
arXiv2015

A Tale of Two Horizons

I revisit the fate of coinciding horizons and the volume between them in the extremal limit of spherically symmetric black holes in four spacetime dimensions, focusing on the Schwarzschild de Sitter black hole for concreteness. The two Killing horizons in the limit spacetime that are traditionally identified with the limiting event horizons of the non-extremal black hole are shown to instead be generated by an enhanced symmetry of the near horizon geometry (NHG). This dismantles the interpretation of the 4-volume between the horizons remaining finite in the extremal limit. The NHG is reinterpreted as a tangent spacetime to the degenerate black hole horizon, and geometrical objects, such as Killing vectors and Killing horizons, are carefully mapped between the bulk and the NHG. The implications for extremal black hole entropy are then discussed.

gr-qc↗
arXiv2014

Gauss-Bonnet Boson Stars with a Single Killing Vector

We construct asymptotically anti-de Sitter boson stars in Einstein-Gauss-Bonnet gravity coupled to a $\frac{D-1}{2}$-tuplet of complex massless scalar fields both perturbatively and numerically in D=5,7,9,11 dimensions. These solutions possess just a single helical Killing symmetry due to the choice of scalar fields. The energy density at the centre of the star characterizes the solutions, and for each choice of the Gauss-Bonnet coupling $α$ we obtain a one parameter family of solutions. All solutions respect the first law of thermodynamics; in the numerical case to within 1 part in $10^6$. We describe the dependence of the angular velocity, mass, and angular momentum of the boson stars on $α$ and on the dimensionality. For D>5, these quantities exhibit damped oscillations about finite central values as the central energy density tends to infinity, where the amplitude of oscillation increases nonlinearly with $α$. In the limit of diverging central energy density, the Kretschmann invariant at the centre of the boson star also diverges. This is in contrast to the D=5 case, where the Kretschmann invariant diverges at a finite value of the central energy density.

gr-qc↗
arXiv2013

Numerical Boson Stars with a Single Killing Vector I: the $D\ge5$ Case

We numerically construct asymptotically anti-de Sitter boson star solutions using a minimally coupled $\frac{D-1}{2}$-tuplet complex scalar field in $D=5,7,9,11$ dimensions. The metric admits multiple Killing vector fields in general, however the scalar fields are only invariant under a particular combination, leading to such boson star solutions possessing just a single helical Killing symmetry. These boson stars form a one parameter family of solutions, which can be parametrized by the energy density at their center. As the central energy density tends to infinity, the angular velocity, mass, and angular momentum of the boson star exhibit damped harmonic oscillations about finite central values, while the Kretschmann invariant diverges, signaling the formation of a black hole in this limit.

hep-th↗
arXiv2013

Numerical Boson Stars with a Single Killing Vector II: the D=3 Case

We complete the analysis of part I in this series (Ref. \cite{Stotyn:2013yka}) by numerically constructing boson stars in 2+1 dimensional Einstein gravity with negative cosmological constant, minimally coupled to a complex scalar field. These lower dimensional boson stars have strikingly different properties than their higher dimensional counterparts, most noticeably that there exists a finite central energy density, above which an extremal BTZ black hole forms. In this limit, all of the scalar field becomes enclosed by the horizon; it does not contract to a singularity, but rather the origin remains smooth and regular and the solution represents a spinning boson star trapped inside a degenerate horizon. Additionally, whereas in higher dimensions the mass, angular momentum, and angular velocity all display damped harmonic oscillations as functions of the central energy density, in $D=3$ these quantities change monotonically up to the bound on the central energy density. Some implications for the holographic dual of these objects are discussed and it is argued that the boson star and extremal BTZ black hole phases are dual to a spontaneous symmetry breaking at zero temperature but finite energy scale.

hep-th↗
arXiv2012

Another Mass Gap in the BTZ Geometry?

We attempt the construction of perturbative rotating hairy black holes and boson stars, invariant under a single helical Killing field, in 2+1-dimensions to complete the perturbative analysis in arbitrary odd dimension recently put forth in \cite{Stotyn:2011ns}. Unlike the higher dimensional cases, we find evidence for the non-existence of hairy black holes in 2+1-dimensions in the perturbative regime, which is interpreted as another mass gap, within which the black holes cannot have hair. The boson star solutions face a similar impediment in the background of a conical singularity with a sufficiently high angular deficit, most notably in the zero-mass BTZ background where boson stars cannot exist at all. We construct such boson stars in the AdS_3 background as well as in the background of conical singularities of periodicities π,2π/3,π/2.

gr-qc↗
arXiv2012

Black Holes and Boson Stars with One Killing Field in Arbitrary Odd Dimensions

We extend the recent D=5 results of Dias, Horowitz and Santos by finding asymptotically AdS rotating black hole and boson star solutions with scalar hair in arbitrary odd spacetime dimension. Both the black holes and the boson stars are invariant under a single Killing vector field which co-rotates with the scalar field and, in the black hole case, is tangent to the generator of the horizon. Furthermore, we explicitly construct boson star and small black hole ($r_+ \ll \ell$) solutions perturbatively assuming a small amplitude for the scalar field, resulting in solutions valid for low energies and angular momenta. We find that just as in D=5, the angular momentum is primarily carried by the scalar field in $D>5$, whereas unlike D=5 the energy is also primarily carried by the scalar field in $D>5$; the thermodynamics in D=5 are governed by both the black hole and scalar field whereas in $D>5$ they are governed primarily by the scalar field alone. We focus on cataloguing these solutions for the spacetime dimensions of interest in string theory, namely $D=5,7,9,11$.

hep-th↗
arXiv2011

Magnetic Charge Can Locally Stabilize Kaluza-Klein Bubbles

We construct a new 2-parameter family of static topological solitons in 5D minimal supergravity which are endowed with magnetic charge and mass. The solitons are asymptotically ${\mathbb R}^4\times S^1$, where the radius of the $S^1$ has a lower bound $R_s\ge R_{min}$. Setting up initial data on a Cauchy slice at a moment of time symmetry, we demonstrate that if $R_s>R_{min}$ these solitons correspond to a perturbatively stable "small" static bubble as well as an unstable "large" static bubble, whereas if $R_s<R_{min}$ there are no static bubbles. The energetics and thermodynamics of the magnetic black string are then discussed and it is shown that the locally stable bubble is the end point of a phase transition for an appropriate range of black string parameters.

hep-th↗
arXiv2010

A General Black String and its Microscopics

Using G2(2) dualities we construct the most general black string solution of minimal five-dimensional ungauged supergravity. The black string has five independent parameters, namely, the magnetic one-brane charge, smeared electric zero-brane charge, boost along the string direction, energy above the BPS bound, and rotation in the transverse space. In one extremal limit it reduces to the three parameter supersymmetric string of five-dimensional minimal supergravity; in another extremal limit it reduces to the three parameter non-supersymmetric extremal string of five-dimensional minimal supergravity. It also admits an extremal limit when it has maximal rotation in the four-dimensional transverse space. The decoupling limit of our general black string is a BTZ black hole times a two sphere. The macroscopic entropy of the string is reproduced by the Maldacena-Strominger-Witten CFT in appropriate ranges of the parameters. When the pressureless condition is imposed, our string describes the infinite radius limit of the most general class of black rings of minimal supergravity. We discuss implications our solution has for extremal and non-extremal black rings of minimal supergravity.

hep-th↗
arXiv2010

A 43-GHz Survey in the ELAIS N2 Area

We describe a survey in the ELAIS N2 region with the VLA at 43.4 GHz, carried out with 1627 independent snapshot observations in D-configuration and covering about 0.5 square degrees. One certain source is detected, a previously-catalogued flat-spectrum QSO at z=2.2. A few (<5) other sources may be present at about the 3sigma level, as determined from positions of source-like deflections coinciding with blue stellar objects, or with sources from lower-frequency surveys. Independently we show how all the source-like detections identified in the data can be used with a maximum-likelihood technique to constrain the 43-GHz source counts at a level of ~7 mJy. Previous estimates of the counts at 43 GHz, based on lower-frequency counts and spectral measurements, are consistent with these constraints, although the present results are suggestive of somewhat higher surface densities at the 7 mJy level. They do not provide direct evidence of intrusion of a previously unknown source population, although the several candidate sources need examination before such a population can be ruled out.

astro-ph.CO↗
arXiv2009

Phase Transitions Between Solitons and Black Holes in Asymptotically AdS/$Z_k$ Spaces

We employ a thermodynamic analysis to determine the phase structure of Eguchi-Hanson solitons, Schwarzschild-AdS/$\mathbb{Z}_k$ black holes and thermal AdS/$\mathbb{Z}_k$. The Euclidean actions are calculated by two equable means: the first uses the Eguchi-Hanson soliton as the thermal background while the second makes use of minimal boundary counterterms in the action necessary to render individual actions finite. The Euclidean actions are then utilised to determine the phase structure in arbitrary odd dimension; it is found that there is a Hawking-Page phase transition and also a phase transition between the black hole and soliton. There is found to be no smooth phase transition governed by an order parameter between AdS/$\mathbb{Z}_k$ and the soliton but nevertheless AdS/$\mathbb{Z}_k$ changes phase by tunneling to the lower energy soliton configuration.

hep-th↗
arXiv2009

Observer Dependent Horizon Temperatures: a Coordinate-Free Formulation of Hawking Radiation as Tunneling

We reformulate the Hamilton-Jacobi tunneling method for calculating Hawking radiation in static, spherically-symmetric spacetimes by explicitly incorporating a preferred family of frames. These frames correspond to a family of observers tied to a locally static timelike Killing vector of the spacetime. This formulation separates the role of the coordinates from the choice of vacuum and thus provides a coordinate-independent formulation of the tunneling method. In addition, it clarifies the nature of certain constants and their relation to these preferred observers in the calculation of horizon temperatures. We first use this formalism to obtain the expected temperature for a static observer at finite radius in the Schwarzschild spacetime. We then apply this formalism to the Schwarzschild-de Sitter spacetime, where there is no static observer with 4-velocity equal to the static timelike Killing vector. It is shown that a preferred static observer, one whose trajectory is geodesic, measures the lowest temperature from each horizon. Furthermore, this observer measures horizon temperatures corresponding to the well-known Bousso-Hawking normalization.

gr-qc↗
arXiv2008

Supergravity on an Atiyah-Hitchin Base

We construct solutions to five dimensional minimal supergravity using an Atiyah-Hitchin base space. In examining the structure of solutions we show that they generically contain a singularity either on the Atiyah-Hitchin bolt or at larger radius where there is a singular solitonic boundary. However for most points in parameter space the solution exhibits a velocity of light surface (analogous to what appears in a Goedel space-time) that shields the singularity. For these solutions, all closed time-like curves are causally disconnected from the rest of the space-time in that they exist within the velocity of light surface, which null geodesics are unable to cross. The singularities in these solutions are thus found to be hidden behind the velocity of light surface and so are not naked despite the lack of an event horizon. Outside of this surface the space-time is geodesically complete, asymptotically flat and can be arranged so as not to contain closed time-like curves at infinity. The rest of parameter space simply yields solutions with naked singularities.

hep-th↗