[Paper Review] Gravitational Radiation from String Cosmology

Ram Brustein, M. Gasperini+2 more|ArXiv.org|Oct 12, 1995

Geophysics and Gravity Measurements3 citations

TL;DR

This paper proposes that string cosmology models generate a stochastic background of gravitational waves with a strongly red-tilted spectrum, peaking at high frequencies. The authors estimate detectability using planned detectors, showing that a portion of the parameter space is accessible to future gravitational-wave observatories.

ABSTRACT

A spectrum of relic stochastic gravitational radiation, strongly tilted towards high frequencies, and characterized by two basic parameters is shown to emerge in a class of string theory models. We estimate the required sensitivity for detection of the predicted gravitational radiation and show that a region of our parameter space is within reach for some of the plannedgravitational-wave detectors.

Motivation & Objective

• To investigate the production of gravitational radiation in string theory-based cosmological models.
• To determine the spectral characteristics of the resulting stochastic gravitational wave background.
• To evaluate the detectability of this background using current and planned gravitational-wave detectors.
• To identify parameter ranges in string cosmology that yield observable gravitational wave signals.

Proposed method

• Analyzes a class of string theory models that incorporate cosmological evolution with non-trivial dilaton and moduli fields.
• Derives the spectrum of relic gravitational radiation using effective field theory techniques in the context of string cosmology.
• Applies the formalism of linearized gravity in a time-dependent background to compute the power spectrum of gravitational waves.
• Considers the role of the dilaton field and its coupling to the gravitational sector in shaping the wave amplitude and frequency distribution.
• Estimates the signal strength and frequency distribution to assess sensitivity requirements for detection.
• Compares the predicted spectrum with the sensitivity curves of planned interferometric detectors such as LIGO and LISA.

Experimental results

Research questions

• RQ1 What is the frequency spectrum of gravitational radiation produced in string cosmology models?
• RQ2 How does the amplitude of the gravitational wave background depend on the parameters of the string model?
• RQ3 Which regions of the model's parameter space produce a detectable gravitational wave signal with current or future detectors?
• RQ4 What is the tilt of the gravitational wave spectrum, and how does it affect observability?
• RQ5 Can the predicted gravitational wave background be distinguished from other astrophysical or cosmological backgrounds?

Key findings

• A stochastic gravitational wave background with a strongly tilted (red-tilted) spectrum is generated in string cosmology models.
• The spectrum peaks at high frequencies, indicating a significant component in the high-frequency band.
• The background is characterized by two fundamental parameters related to the string model's dynamics and initial conditions.
• A portion of the model's parameter space produces a signal amplitude within the sensitivity range of planned gravitational-wave detectors.
• The predicted signal could be detectable by future interferometric detectors such as LIGO and LISA, depending on the model parameters.
• The results suggest that string cosmology could provide a testable prediction through high-frequency gravitational wave observations.