Scholarship & Research
Permanent URI for this communityhttps://scholarworks.montana.edu/handle/1/1
Browse
3 results
Search Results
Item Improved gravitational-wave constraints on higher-order curvature theories of gravity(American Physical Society, 2021-07) Perkins, Scott E.; Nair, Remya; Silva, Hector O.; Yunes, NicolásGravitational wave observations of compact binaries allow us to test general relativity (and modifications thereof) in the strong and highly dynamical field regime of gravity. Here, we confront two extensions to general relativity, dynamical Chern-Simons, and Einstein-dilaton-Gauss-Bonnet theories, against the gravitational wave sources from the GWTC-1 and GWTC-2 catalogs by the LIGO-Virgo Collaboration. By stacking the posterior of individual events, we strengthen the constraint on the square root of the coupling parameter in Einstein-dilaton-Gauss-Bonnet gravity to √αEdGB<1.7 km, but we are unable to place meaningful constraints on dynamical Chern-Simons gravity. Importantly, we also show that our bounds are robust to (i) the choice of general-relativity base waveform model, upon which we add modifications, (ii) unknown higher post-Newtonian order terms in the modifications to general relativity, (iii) the small-coupling approximation, and (iv) uncertainties on the nature of the constituent compact objects.Item Surface of rapidly-rotating neutron stars: Implications to neutron star parameter estimation(American Physical Society, 2021-03) Silva, Hector O.; Pappas, George; Yunes, Nicolás; Yagi, KentThe Neutron star Interior Composition Explorer (NICER) is currently observing the x-ray pulse profiles emitted by hot spots on the surface of rotating neutron stars allowing for an inference of their radii with unprecedented precision. A critical ingredient in the pulse profile model is an analytical formula for the oblate shape of the star. These formulas require a fitting over a large ensemble of neutron star solutions, which cover a wide set of equations of state, stellar compactnesses and rotational frequencies. However, this procedure introduces a source of systematic error, as (i) the fits do not describe perfectly the surface of all stars in the ensemble and (ii) neutron stars are described by a single equation of state, whose influence on the surface shape is averaged out during the fitting procedure. Here we perform a first study of this systematic error, finding evidence that it is subdominant relative to the statistical error in the radius inference by NICER. We also find evidence that the formula currently used by NICER can be used in the inference of the radii of rapidly rotating stars, outside of the formula’s domain of validity. Moreover, we employ an accurate enthalpy-based method to locate the surface of numerical solutions of rapidly rotating neutron stars and a new highly accurate formula to describe their surfaces. These results can be used in applications that require an accurate description of oblate surfaces of rapidly rotating neutron stars.Item Fundamental physics implications on higher-curvature theories from the binary black hole signals in the LIGO-Virgo Catalog GWTC-1(2020-04) Nair, Remya; Perkins, Scott; Silva, Hector O.; Yunes, NicoGravitational-wave astronomy offers not only new vistas into the realm of astrophysics, but it also opens an avenue for probing, for the first time, general relativity in its strong-field, nonlinear, and dynamical regime, where the theory’s predictions manifest themselves in their full glory. We present a study of whether the gravitational-wave events detected so far by the LIGO-Virgo scientific collaborations can be used to probe higher-curvature corrections to general relativity. In particular, we focus on two examples: Einstein-dilaton-Gauss-Bonnet and dynamical Chern-Simons gravity. We find that the two events with a low-mass m ≈ 7M⊙ BH (GW151226 and GW170608) place stringent constraints on Einstein-dilaton-Gauss-Bonnet gravity, α1/2 . 5.6 km, whereas EdGB dynamical Chern-Simons gravity remains unconstrained by the gravitational-wave observations analyzed.