Research

Modified gravity from a geometric perspective

My research is in theoretical gravitation, cosmology and relativistic astrophysics. I work on geometric extensions of General Relativity and on their applications to black holes, compact objects, cosmology and gravitational-wave signatures. A central theme of my work is that gravity need not be described only by curvature: depending on the geometric structure, torsion, nonmetricity, or an independent affine connection can become part of the gravitational dynamics.

General Relativity is remarkably successful, but it is not the only possible geometric description of gravity. One can modify the gravitational theory by adding new invariants to the action, by changing the geometric structure of spacetime, or by introducing additional fields that interact with the metric or the connection. These possibilities are not completely separate: many theories can be written in more than one language, and the same physical idea can sometimes appear as curvature, torsion or nonmetricity depending on the variables used.

My current work focuses mainly on non-Riemannian and gauge-theoretic formulations of gravity. This includes teleparallel gravity, symmetric teleparallel gravity, Poincaré gauge theory and metric-affine gravity. In these frameworks the choice of geometry determines which quantities are dynamical, how matter couples to gravity, and which new physical effects can appear.

Black holes and compact objects

Exact solutions, regular black holes, hairy configurations, spin-charge interactions, superradiance and observational degeneracies.

Cosmology

Background dynamics, perturbations, late-time acceleration and the role of torsion and nonmetricity in homogeneous and isotropic universes.

Gravitational waves

Propagation, polarizations, extra degrees of freedom and possible signatures of non-Riemannian geometry.

Foundations of gravity

Geometric reformulations of gravity, gauge principles, stability, constraints and the classification of post-Riemannian fields.

Representation of possible ways of modifying General Relativity — Schematic representation of different routes beyond General Relativity. The figure is useful because it shows that many apparently different theories are connected: changing the geometric structure, adding invariants, introducing extra fields or considering quantum-gravity inspired corrections can lead to overlapping descriptions.

Teleparallel and symmetric teleparallel gravity

Teleparallel gravity rewrites the gravitational interaction in terms of torsion instead of curvature. In the teleparallel equivalent of General Relativity, the curvature of the Weitzenböck connection vanishes and the dynamics can be written using the torsion scalar $T$ . The usual Ricci scalar $\bar{R}$ and the torsion scalar differ by a boundary term,

\bar{R}=-T+B .

This identity explains why the teleparallel equivalent of General Relativity gives the same field equations as Einstein gravity, while also opening a different path for constructing modified theories. Once one modifies the torsional action, for example through functions of $T$ , boundary terms, scalar couplings or Gauss–Bonnet-type extensions, the resulting theory is generally no longer equivalent to the usual curvature-based modification.

I have worked on several aspects of teleparallel gravity: cosmological perturbations, post-Newtonian limits, black-hole solutions, scalarization, thick accretion disks, gravitational-wave propagation and the relation between teleparallel, symmetric teleparallel and curvature-based descriptions. This line of work also led to the review Teleparallel Gravity: From Theory to Cosmology.

Teleparallel Gravity: From Theory to Cosmology, Rept. Prog. Phys. 86 (2023) 026901.
Spontaneous Scalarization of Black Holes in Gauss-Bonnet Teleparallel Gravity, Phys. Rev. D 107 (2023) 104013.
Distinctive Features of Hairy Black Holes in Teleparallel Gauss-Bonnet Gravity, Phys. Rev. D 108 (2023) 064044.
Black hole solutions in scalar-tensor symmetric teleparallel gravity, JCAP 08 (2022) 082.

Metric-affine gravity, torsion and nonmetricity

A broader route is to move from Riemannian geometry to a metric-affine geometry. In this setting the metric and the affine connection are independent objects. The independent connection can carry torsion and nonmetricity,

T^{\lambda}{}_{\mu\nu}=2\tilde{\Gamma}^{\lambda}{}_{[\mu\nu]}, \qquad Q_{\lambda\mu\nu}=\tilde{\nabla}_{\lambda}g_{\mu\nu}.

The connection can be decomposed into the Levi-Civita part plus post-Riemannian pieces,

\tilde{\Gamma}^{\lambda}{}_{\mu\nu} = \Gamma^{\lambda}{}_{\mu\nu} + K^{\lambda}{}_{\mu\nu} + L^{\lambda}{}_{\mu\nu},

where $K^{\lambda}{}_{\mu\nu}$ contains torsion and $L^{\lambda}{}_{\mu\nu}$ contains nonmetricity. This makes metric-affine gravity a natural framework for studying new gravitational degrees of freedom associated with spin, dilation and shear-type geometric structures.

In recent years I have studied exact black-hole solutions, algebraic classification, cosmological perturbations, stability and gravitational waves in metric-affine and Poincaré gauge theories. A major motivation is to understand when torsion and nonmetricity are merely auxiliary fields and when they become genuinely dynamical, propagating sectors with possible signatures in astrophysics or cosmology.

New black hole solutions with a dynamical traceless nonmetricity tensor in Metric-Affine Gravity, JCAP 02 (2023) 018.
Cosmological Perturbation Theory in Metric-Affine Gravity, Phys. Rev. D 110 (2024) 024017.
Stability in cubic metric-affine gravity, Phys. Rev. D 111 (2025) 084058.
Gravitational waves in Cubic Metric-Affine Gravity, to appear in Phys. Rev. D.
A gravitational spin-orbit interaction in Poincaré gauge theory, Phys. Lett. B 873 (2026) 140126.

Black holes, gravitational waves and phenomenology

A large part of my research connects formal gravitational theory with concrete physical systems. Black holes are especially useful because they test the nonlinear regime of gravity and expose whether extra geometric degrees of freedom can be hidden, sourced, screened or observed. My work in this direction includes regular black holes with scalar hair, black holes in Weyl-Cartan and metric-affine geometries, teleparallel scalarization, electromagnetic couplings to torsion, and superradiance in Poincaré gauge theory.

I am also interested in gravitational waves beyond the Riemannian description. In these theories, one can ask whether torsion or nonmetricity changes wave propagation, introduces new polarizations, or produces additional tensor, vector or scalar modes. This provides a bridge between the mathematical structure of the theory and future tests with gravitational-wave observations.

Geometrically Regular Black Holes with Hedgehog Scalar Hair, to appear in Phys. Rev. D.
Coupling electromagnetism to torsion: Black holes and spin-charge interactions, Phys. Rev. D 113 (2026) no.4.
An exact five dimensional Weyl-geometry Gauss-Bonnet black hole, Phys. Lett. B 869 (2025) 139869.
Black hole superradiance in Poincaré gauge theory.

Cosmology and dynamical systems

My earlier work also studied late-time acceleration, dark energy and cosmological reconstruction in modified gravity. Many cosmological models reduce to systems of ordinary differential equations, and this makes dynamical-systems methods a powerful way of understanding their phase-space structure, fixed points and possible cosmic histories. This work connects naturally with more recent questions about perturbations and gravitational waves in teleparallel and metric-affine theories.

Dynamical systems applied to cosmology: dark energy and modified gravity, Phys. Rept. 775-777 (2018) 1-122.
Cosmology of cubic Poincaré gauge gravity, Phys. Dark Univ. 52 (2026) 102249.
Gauge-invariant cosmological perturbations in Type 3 New General Relativity and background-hierarchy bounds.
The CosmoVerse White Paper: Addressing observational tensions in cosmology with systematics and fundamental physics, Phys. Dark Univ. 49 (2025) 101965.

A complete list of publications is available on my Papers page, as well as through INSPIRE-HEP and Google Scholar.