# Teukolsky

Install this package!A Mathematica package for computing solutions to the Teukolsky equation. Note this package depends upon the SpinWeightedSpheroidalHarmonics and the KerrGeodesics package to run.

Explicitly the package computes solutions to:

\[\Delta^{-s} \dfrac{d}{dr} \bigg[\Delta^{s+1}\dfrac{d R}{dr}\bigg] + \bigg[\frac{K^2 - 2 i s (r-M)K}{\Delta} + 4 i s \omega r - \lambda \bigg]R = \mathcal{T} \nonumber\]where

$\Delta = r^2 - 2Mr + a^2$

$K=(r^2 + a^2)\omega - a m$

$s$ is the spin-weight of the perturbing field

$\lambda$ is the spin-weighted spheroidal eigenvalue

$\omega$ is the mode frequency

$\mathcal{T}$ is the source

Currently the source has been implemented for a point particle moving along a circular orbit in Kerr spacetime. As an example, the flux in this case for the $l=2,m=2$ mode is easily computed using:

```
a = 0.9`32;
r0 = 10.`32;
orbit = KerrGeoOrbit[a, r0, 0, 1];
s = -2; l = 2; m = 2; n = 0; k = 0;
mode = TeukolskyPointParticleMode[s, l, m, n, k, orbit];
mode["Fluxes"]
```

This returns an association with the results:

```
<|"FluxInf" -> 0.000022273000551180497057, "FluxHor" -> -5.9836792133833631984*10^-8, "FluxTotal" -> 0.000022213163759046663425|>
```

Note the high precision of the input values for $a$ and $r_0$. Currently this is often a requirement to get an accurate result.

## Homogeneous solutions

The homogeneous solutions are also easily computed. They can be extracted from the `mode`

object above using `R = mode["Radial"]`

. This returns a `TeukolskyRadialFunction[]`

which can be evaluated at a given radius, i.e., `R[20.]`

. The homogeneous solutions can also be computed directly via the `TeukolskyRadial[s, l, m, a, ω]`

function.

## Renormalized angular momentum

Under the hood the Teukolsky package defaults to using the MST method for computing the homogeneous solutions (Sasaki-Nakamura methods are in development). A key part of the MST method is the calculation of the renormalized angular momentum, $\nu$. This can be computed directly via

```
ν = RenormalizedAngularMomentum[s, l, m, a, ω]
```

### Further examples

Example notebooks can be found in the Mathematica Toolkit Examples repository.

## Installation

We recommend users install the package using Mathematica’s Paclet system. For instructions see the Mathematica package installation page. This will install the latest version and automatically handle upgrades as new releases become available.

Alternatively, the latest official release can be found at: . We recommend only developers download the code directly from GitHub.

## Citation

In addition to citing the Black Hole Perturbation Toolkit as suggested on the front page we also recommend citing the version of the specific package version you use via the citation information on the package’s Zenodo page.

## Authors and contributors

Barry Wardell, Niels Warburton, Marc Casals, Adrian Ottewill, Chris Kavanagh, Leanne Durkan, Ben Leather, Theo Torres