- The paper introduces a novel relativistic framework that reconciles MOND predictions with key cosmological observations such as the CMB and Matter Power Spectrum.
- It employs a modified scalar-tensor-vector approach, enhancing TeVeS by integrating a new scalar degree of freedom to reproduce MOND behavior and ensure stability.
- Numerical results demonstrate near-perfect alignment with Planck and SDSS data, marking a significant advance in integrating galactic dynamics and cosmology.
New Relativistic Theory for Modified Newtonian Dynamics
The paper authored by Constantinos Skordis and Tom Zlosnik presents a novel relativistic gravitational theory designed to address the discrepancies in the traditional understanding of dark matter (DM) through a framework known as Modified Newtonian Dynamics (MOND). MOND posits alternative gravitational dynamics that can potentially illuminate astrophysical phenomena typically attributed to DM. This theory's primary achievement is the alignment of MOND with cosmological observations, particularly the Cosmic Microwave Background (CMB) and Matter Power Spectrum (MPS), establishing a consistent theory on both galactic and cosmological scales.
Theoretical Framework
The proposed theory is grounded in several core phenomenological requirements. These include the seamless transition from general relativity (GR) at high potential gradients to MOND behavior when potential gradients are low, alignment with cosmological observations like the CMB and MPS, accurate reproduction of gravitational lensing data without relying on DM halos, and propagation of gravitational waves (GWs) at the speed of light. This paper challenges the belief that a fully satisfactory relativistic theory embodying all MOND predictions while maintaining cosmological consistency is unattainable.
In constructing the new theory, the authors embrace a scalar-tensor-vector framework analogous to TeVeS but with critical modifications. The theory introduces a new degree of freedom with a scalar field articulated in a way that it conforms to both the CMB and MPS observations, resembles MOND at galactic scales, and resolves discrepancies apparent in previous constructs such as TeVeS.
Cosmological and Galactical Implications
Crucially, the new theory reconciles MOND's empirical success in predicting galactic rotation curves with the CMB data traditionally explained using cold DM models. The scalar field in this construct provides a dust-like density scaling function fitting observed densities during critical epochs between radiation-matter equality and recombination, a notable advance in MOND's integration into cosmological modeling. This is achieved while avoiding ghost instabilities, suggesting the theory is a suitable candidate for further macro-scale applications.
Numerical Outcomes and Stability
Numerical computations of the CMB spectra executed through a customized Boltzmann code demonstrate near-perfect alignment with Planck data, further corroborating the theory's validity. Moreover, the linear MPS is shown to fit Sloan Digital Sky Survey (SDSS) observations, providing essential evidence of the theory's applicability to observable universe dynamics. The theory’s stability is rigorously tested in the Minkowski spacetime, ensuring consistency and absence of ghost instabilities in the scalar and tensor perturbations and providing a stable background framework necessary for its integration into larger theoretical models.
Future Directions
This theory proposes a significant step towards a MOND-centric cosmological model that could yield deeper insights into the gravity-dominated universe. Prospective work could focus on understanding the transition from the linear to the nonlinear regime, exploring the scattering and interaction dynamics of baryonic matter under the new framework, and investigating the emerging phenomena in gravitational wave observations. Additionally, comparisons with data from upcoming cosmological surveys and gravitational wave detectors might unveil further refinements and extensions for this theoretical framework.
In conclusion, Skordis and Zlosnik have provided a promising path towards integrating MOND with broader cosmological understanding, challenging the prevailing dark matter paradigms and offering a new perspective on gravitational dynamics across different scales. This research lays a robust foundation for future exploration and evaluation of modified gravitational theories through both theoretical examination and empirical validation.