15 research outputs found
Oscillon formation during inflationary preheating with general relativity
We study the non-perturbative evolution of inflationary fluctuations during
preheating using fully non-linear general-relativistic field-theory
simulations. We choose a single-field inflationary model that is consistent
with observational constraints and start the simulations at the end of
inflation with fluctuations both in the field and its conjugate momentum.
Gravity enhances the growth of density perturbations, which then collapse and
virialize, forming long-lived stable oscillon-like stars that reach
compactnesses . We find that
increases for larger field models, until it peaks due to the
interplay between the overdensity growth and Hubble expansion rates. Whilst
gravitational effects can play an important role in the formation of compact
oscillons during preheating, the objects are unlikely to collapse into
primordial black holes without an additional enhancement of the initial
inflationary fluctuations.Comment: 7 pages. 4 figures. Movie: https://youtu.be/vTl9agMfPB0. Matches
version published in PR
Cosmic String Loop Collapse in Full General Relativity
We present the first fully general relativistic dynamical simulations of
Abelian Higgs cosmic strings using 3+1D numerical relativity. Focusing on
cosmic string loops, we show that they collapse due to their tension and can
either (i) unwind and disperse or (ii) form a black hole, depending on their
tension and initial radius. We show that these results can be predicted
using an approximate formula derived using the hoop conjecture, and argue that
it is independent of field interactions. We extract the gravitational waveform
produced in the black hole formation case and show that it is dominated by the
and mode. We also compute the total gravitational wave energy
emitted during such a collapse, being of the initial total
cosmic string loop mass, for a string tension of and
radius . We use our results to put a bound on the production
rate of planar cosmic strings loops as .Comment: Movies:
https://www.youtube.com/playlist?list=PLSkfizpQDrcaAxkuQ3BtjILn_tJu-jXx
Coherent Gravitational Waveforms and Memory from Cosmic String Loops
We construct, for the first time, the time-domain gravitational wave strain
waveform from the collapse of a strongly gravitating Abelian Higgs cosmic
string loop in full general relativity. We show that the strain exhibits a
large memory effect during merger, ending with a burst and the characteristic
ringdown as a black hole is formed. Furthermore, we investigate the waveform
and energy emitted as a function of string width, loop radius and string
tension . We find that the mass normalized gravitational wave energy
displays a strong dependence on the inverse of the string tension
, with at the percent level, for the regime where .
Conversely, we show that the efficiency is only weakly dependent on the initial
string width and initial loop radii. Using these results, we argue that
gravitational wave production is dominated by kinematical instead of
geometrical considerations.Comment: 15 pages, 16 figures, 2 YouTube movies: https://youtu.be/-dhYA2788LA
https://youtu.be/0sSH54gXu4
Revisiting the cosmic string origin of GW190521
For the first time we analyse gravitational-wave strain data using waveforms constructed from
strong gravity simulations of cosmic string loops collapsing to Schwarzschild black holes; a previously
unconsidered source. Since the expected signal is dominated by a black-hole ringdown, it can mimic
the observed gravitational waves from high-mass binary black hole mergers. To illustrate this,
we consider GW190521, a short duration gravitational-wave event observed in the third LIGO–
Virgo–KAGRA observing run. We show that describing this event as a collapsing cosmic string
loop is favoured over previous cosmic string analyses by an approximate log Bayes factor of 22.
The binary black hole hypothesis is still preferred, mostly because the cosmic string remnant is
non-spinning. It remains an open question whether a spinning remnant could form from loops
with angular momentum, but if possible, it would likely bring into contention the binary black
hole preference. Finally, we suggest that searches for ringdown-only waveforms would be a viable
approach for identifying collapsing cosmic string events. This work opens up an important new
direction for the cosmic-string and gravitational-wave communities
Spinning primordial black holes formed during a matter-dominated era
We study the formation of spinning primordial black holes during an early
matter-dominated era. Using non-linear 3+1D general relativistic simulations,
we compute the efficiency of mass and angular momentum transfer in the process
-- which we find to be and ,
respectively. We show that subsequent evolution is important due to the seed
PBH accreting non-rotating matter from the background, which decreases the
dimensionless spin. Unless the matter era is short, we argue that the final
dimensionless spin will be negligible.Comment: 12 pages, 5 figures. 1 YouTube video
$\href{https://youtu.be/CC4xBLol4aE}{here}
GRDzhadzha: A code for evolving relativistic matter on analytic metric backgrounds
GRDzhadzha is an open-source code for relativistic simulations of matter
fields on curved spacetimes that admit an analytic description (e.g. stationary
black holes). It is based on the publicly available 3+1D numerical relativity
code GRChombo. Such a description is valid where the density of the matter is
small compared to the curvature scale of the spacetime, which is the case for
many physical scenarios - for example, dark matter environments. The approach
offers significant savings on memory and speed compared to running full
numerical relativity simulations, since the metric variables and their
derivatives are calculated analytically, and therefore are not evolved or
stored on the grid. This brief paper introduces the code and gives details of
some applications for which it has already been used.Comment: Submitted for review in the Journal of Open Source Software; Comments
welcome; The code can be found at https://github.com/GRChombo/GRDzhadzha.gi
GRChombo: An adaptable numerical relativity code for fundamental physics
GRChombo is an open-source code for performing Numerical Relativity time
evolutions, built on top of the publicly available Chombo software for the
solution of PDEs. Whilst GRChombo uses standard techniques in NR, it focusses
on applications in theoretical physics where adaptability, both in terms of
grid structure, and in terms of code modification, are key drivers
CTTK: A new method to solve the initial data constraints in numerical relativity
In numerical relativity simulations with non-trivial matter configurations,
one must solve the Hamiltonian and momentum constraints of the ADM formulation
for the metric variables in the initial data. We introduce a new scheme based
on the standard Conformal Transverse-Traceless (CTT) decomposition, in which
instead of solving the Hamiltonian constraint as a 2nd order elliptic equation
for a choice of mean curvature , we solve an algebraic equation for for
a choice of conformal factor. By doing so, we evade the existence and
uniqueness problem of solutions of the Hamiltonian constraint without using the
usual conformal rescaling of the source terms. This is particularly important
when the sources are fundamental fields, as reconstructing the fields'
configurations from the rescaled quantities is potentially problematic. Using
an iterative multigrid solver, we show that this method provides rapid
convergent solutions for several initial conditions that have not yet been
studied in numerical relativity; namely (i) periodic inhomogeneous spacetimes
with large random Gaussian scalar field perturbations and (ii) asymptotically
flat black hole spacetimes with rotating scalar clouds.Comment: 13 pages, 4 figures, 1 appendix. Comments welcom