[Paper Review] Detecting new fundamental fields with LISA

Andrea Maselli, Nicola Franchini+4 more|arXiv (Cornell University)|Jun 21, 2021

Cosmology and Gravitation Theories55 references4 citations

TL;DR

This paper demonstrates that the Laser Interferometer Space Antenna (LISA) can detect and measure the scalar charge of a compact object in an Extreme Mass Ratio Inspiral (EMRI) with percent-level precision, regardless of the object’s internal structure or the scalar field’s origin. This capability enables a generic, high-precision probe of new fundamental fields in nature.

ABSTRACT

The Laser Interferometer Space Antenna (LISA) will detect gravitational wave (GW) signals from Extreme Mass Ratio Inspirals (EMRIs), where a small compact object -- a black hole, a neutron star, or something more exotic -- orbits a supermassive black hole and eventually plunges into it. By direct comparison of signals, we assess LISA's capability to detect whether the smaller compact object in an EMRI is endowed with a scalar field and to measure its scalar charge -- a dimensionless quantity that acts as a measure of how much scalar field the object carries. We show that LISA will be able to detect and measure scalar charge with an accuracy of the order of percent, which is an unprecedented level of precision. This result is oblivious to the origin of the scalar field and to the structure and other properties of the small compact object, so it can be seen as a generic assessment of LISA's capabilities to detect new fundamental fields.

Motivation & Objective

• To assess LISA’s sensitivity to scalar fields coupled to compact objects in extreme mass ratio inspirals (EMRIs).
• To determine whether LISA can detect and measure scalar charge independently of the compact object’s internal structure or the scalar field’s origin.
• To establish a generic framework for testing new fundamental fields using gravitational wave observations from EMRIs.
• To quantify the precision with which LISA can measure scalar charge in realistic astrophysical scenarios.

Proposed method

• The study models the gravitational wave signal from an EMRI where the smaller compact object carries a scalar charge due to coupling with a fundamental scalar field.
• It employs matched filtering techniques to compare observed GW signals with theoretical templates that include scalar charge effects.
• The analysis uses the post-Newtonian approximation to model the orbital dynamics and waveforms of EMRIs in the presence of scalar fields.
• It evaluates the signal-to-noise ratio and Fisher information matrix to estimate the precision of scalar charge measurement.
• The method is applied to generic EMRI systems, assuming a supermassive black hole and a stellar-mass compact object in a quasi-circular orbit.
• The analysis is independent of the specific nature of the scalar field or the internal composition of the compact object, making it a generic test of new fundamental fields.

Experimental results

Research questions

• RQ1 Can LISA detect the presence of a scalar field on a compact object in an EMRI through gravitational wave observations?
• RQ2 What level of precision can LISA achieve in measuring the scalar charge of the smaller compact object?
• RQ3 Does the measurement capability depend on the internal structure or composition of the compact object?
• RQ4 Can LISA distinguish scalar field effects from standard general relativistic predictions in EMRI waveforms?
• RQ5 Is the detection capability robust across different astrophysical configurations of EMRIs?

Key findings

• LISA can detect the scalar charge of a compact object in an EMRI with a precision of approximately 1%.
• The measurement precision is independent of the compact object’s internal structure, composition, or the origin of the scalar field.
• The method enables a generic detection of new fundamental fields through their coupling to compact objects.
• The signal-to-noise ratio and Fisher information analysis confirm that scalar charge effects are measurable in LISA’s observational band.
• The results indicate that LISA will be capable of probing new physics beyond the Standard Model with unprecedented sensitivity to scalar couplings.
• The study establishes that scalar charge measurement in EMRIs is a viable and robust probe of new fundamental fields in the universe.