Several modifications to general relativity have been proposed to explain the nature of dark energy and the accelerated expansion of the Universe. In this talk, I will review the present status of modified theories of gravity in the light of astrophysical probes of gravity in the weak-field regime, ranging from stars to cosmological scales. I begin by setting the scene for how theories beyond...
Direct detection of scattering events of dark matter off ordinary atoms is a critical goal that would allow us to extract information about the nature of the dark matter particle. I will give an overview of the theory underlying the direct detection experiments and on the current status of these experiments. I will discuss some future prospects, focusing on the developments towards direct...
Tachyonic preheating is one of a few compelling mechanisms for transitioning from an inflationary, empty Universe to a hot radiation dominated Universe. The 2PI formalism allows for a correct quantum treatment of particle production and thermalisation, and is well suited for numerical implementation on the lattice. I will present an investigation of tachyonic preheating, aimed at updating...
We study symmetry-breaking inflation within the framework of metric-affine gravity. By introducing a non-minimal coupling, $\beta(\phi)\tilde{\cal R}$, between the Holst invariant and the inflaton, both small-field and large-field inflationary predictions can be brought into agreement with the latest observational constraints. Remarkably, even for sub-Planckian vacuum expectation values,...
Currently, the search for primordial gravitational waves is largely focused on detecting the parity-odd polarization pattern in the Cosmic Microwave Background—the B-modes. Accurately interpreting B-mode measurements depends heavily on understanding their production mechanisms. A particularly compelling scenario involves gravitational wave generation through the interaction of axion with gauge...
The Hubble Tension is the discrepancy between the measured value of the Hubble parameter $H_0$ and its $\Lambda$CDM model prediction using CMB data. New Early Dark Energy (NEDE) addresses this tension using a triggered phase transition in the dark sector. In this work we constrain the properties of NEDE using recent CMB and supernovae datasets, as well as the new BAO data from the DESI survey....
The Palatini formulation of gravity has been successfully used to motivate several observationally viable models of inflationary expansion. While the Palatini and metric formulations are equivalent in minimally coupled gravity, non-minimal scalar models are phenomenologically distinct depending on which formulation is used. At the same time, the recent hybrid approach to metric and Palatini...
We study freeze-in production of dark matter (DM) at temperatures far below the dark matter mass. The temperature of the Standard Model (SM) thermal bath may have never been high such that dark matter production via thermal emission has been Boltzmann suppressed. This allows for a significant coupling between the SM and DM, which is being probed by the direct DM detection experiments and...
Direct detection of light dark matter can be significantly enhanced by up-scattering of dark matter with energetic particles in the cosmic ambient. This boosted dark matter flux can reach kinetic energies up to tens of MeV, while the typical kinetic energies of GeV mass dark matter particles in the Milky Way halo are of the order of keV. Dark matter boosted by energetic diffuse supernova...
In the phenomenon of black hole superradiance a rotating black hole loses its angular momentum to a growing cloud of particles. It has been successfully used to place limits on ultralight particles, such as axions and dark photons, with masses $\mu\sim 10^{-20}-10^{-18}$ eV and $\mu\sim 10^{-12}-10^{-11}$ eV. However, measurements of black hole spins are statistical in nature and have large...
First-order phase transitions at the electroweak scale are predicted by many Standard Model extensions. They could create a stochastic gravitational wave background observable in the millihertz range today. The next-generation spaceborne observatory LISA has the potential of observing these backgrounds. However, possible phase transition signals will be buried under instrument noises and a...
The frequency range of gravitational waves from first-order cosmological phase transitions will be investigated by the upcoming space-based gravitational wave observatory LISA. If we see a signal of cosmological origin, we need to be able to deduce the parameters of the phase transition from the gravitational wave signal to understand the physics behind it. This requires simulations of the...
An oscillating curvature of the spacetime can drive the production of dark matter during reheating, and accurately quantifying this requires the use of both non-perturbative and non-equilibrium methods. In our work, we compare the particle production on a non-minimally coupled scalar field when computed using a classical lattice approach to previous work utilizing Hartree-level 2PI-methods....
Palatini F(R,X) gravity, with X the inflaton kinetic term, proved to be a powerful framework for generating asymptotically flat inflaton potentials. Here we show that the general form of the F(R,X) potential also provides a tail that generates, in principle, quintessential behavior for dark energy. We describe a few examples that fit the observed value of the cosmological constant and discuss...
In this talk I will discuss a recently studied extension of the
natural inflation model comprising a non -
Abelian gauge sector coupled to the axion -
inflaton kinetic term . I will show how such non -
minimal coupling serves as a source of friction for the rolling
inflaton granting at least sixty e -
folds of accelerated expansion for sub -
Planckian values of the axion...
Magnetic monopoles are a common prediction of early universe phase transitions. In particular, any type of a grand unified theory phase transition will produce magnetic monopoles, and it is thought that these monopoles would come to dominate the energy density of the universe. This consitutes the 'monopole problem' of grand unification, which theories of inflation solve by diluting the energy...
Future space-based interferometers offer an unprecedented opportunity to detect signals from the stochastic gravitational wave background originating from a first-order phase transition at the electroweak scale. The phase transition is accompanied by a change of the equation of state from that of pure radiation. In this work we study the effect of this change on the power spectrum of...
The stress energy tensor we all know is related to the existence of a metric. But the metric is not the only character we can take into account when studying a theory of gravity. We can also consider an independent connection. If we do so we will have the hypermomentum tensor in the game too. This can be related to quantities such as torsion and non metricity. What is the role of these...
Lorentz gauge theory of gravity with spontaneous symmetry breaking field provides successful description of ΛCDM model, as well as generalised black hole solutions compared to those in General Relativity. This talk summarises these extensions provided by such theory and explores whether this can be realised with different symmetry group, Euclidean gauge for example, and how this will affect...
Cosmological first order phase transitions are a promising source of gravitational waves, and a possible explanation of the baryon asymmetry and dark matter abundance. Predicting the phenomenological consequences of such phase transitions requires knowledge of the expansion velocity of the bubbles formed in a phase transition. In this talk, I will present WallGo, a software package for the...
One of the primary objectives of the LISA mission is to measure and characterize the stochastic gravitational-wave background (SGWB). Achieving this goal will allow LISA to explore various domains, including astrophysics, cosmology, and particle physics. This talk focuses on the latter, specifically on physics beyond the Standard Model that involves strong first-order phase transitions. We...
Euclid is the cosmology satellite of the European Space Agency (ESA). Its main goal is to solve the mystery of dark energy: what is causing the accelerated expansion of the universe. Euclid was launched in July 2023, and it has been collecting data since February 2024. One of the nine Euclid data processing centers is operating in Finland.
The first major public data release, the so-called...
The Laser Interferometer Space Antenna (LISA) mission is a space-based gravitational wave interferometer set to launch in 2035, and which has now formally been adopted by ESA. LISA will search for gravitational waves in the millihertz frequency range, which is expected to contain gravitational waves of both astrophysical and cosmological origin. To prepare for the future launch of LISA and the...
In the phase space perspective, scalar field slow roll inflation is described by a heteroclinic orbit from a saddle type fixed point to a final attractive point. In many models the saddle point resides in the scalar field asymptotics, thus for a comprehensive view of the dynamics a global phase portrait is necessary. For this task in the literature one encounters dynamical variables that...
Pulsars, which are very rapidly spinning neutron stars, can be instrumental in solving the puzzle, which has perplexed the minds of the scientific community for almost a century – dark matter (DM). In the talk I will mainly focus on the light DM candidates that can be searched for in pulsar observables. The ultralight scalar field DM (also known as "fuzzy" DM), consisting of bosons with...
First-order phase transitions represent a golden opportunity into uncovering new physics as well as into the QCD phase diagram. These transitions typically proceed through nucleation, expansion and collision of bubbles. As a consequence, the spectrum depends on out-of-equilibrium properties that are challenging to obtain, such as the wall speed. In this talk I will review recent progress in...
Cosmological first-order phase transitions may have generated an observable gravitational wave background, offering a unique probe of beyond-Standard-Model physics. A crucial step in predicting this background is the reliable computation of bubble nucleation rates. In this talk, I will give an overview of recent advancements in perturbative high-temperature nucleation rate calculations. These...
The gravitational wave module in the Pencil Code is a versatile tool for computing the time-dependent three-dimensional strain field from a range of different sources in the early universe ranging from phase-transitional hydrodynamic and magnetohydrodynamic stresses to inflationary ones involving electromagnetic and axion pseudoscalar stresses. The solver utilizes the analytic solution for...
In the context of $f(R)$ gravity, as well as other extended theories of gravity, the correct counting of globally well-defined linear dynamical modes (i.e. gravitational-wave polarisations) has recently drawn a vivid interest. In this talk, we present a consistent approach shedding light on such issues for both so-called degenerate and non-degenerate $f(R)$ models embedded in Minkowski and de...
In this talk I will review the succesful search for Hellings-Downs correlations by the NANOGrav collaboration and the search for new physics with pulsar timing data. In particular, I will show the first model-independent search going beyond the simple power-law fit to characterise the frequency spectrum of the signal observed by the collaboration, allowing for a running of the spectral index....
Cosmological first-order phase transitions may have played a significant role in the formation of baryon asymmetry and dark matter, potentially leaving an observable gravitational wave signature. In this talk, I will focus on the possibility of primordial black hole formation from slow and strongly supercooled transitions. I will describe how the stochastic nature of the bubble nucleation...
Primordial black holes (PBHs) are a compelling dark matter candidate that can be effectively probed through their gravitational wave (GW) signatures. In this talk, I will focus on standard scenarios in which PBHs form via the collapse of sizeable primordial curvature fluctuations. I will discuss what current pulsar timing array (PTA) measurements can tell us about stellar-mass PBHs and whether...
The running-mass inflation model generates the primordial curvature perturbation spectrum that is consistent with observations at the pivot scale but exhibits a very large running at smaller scales. This creates favourable conditions for the formation of primordial black holes. In the current work we analyse a novel mechanism that provides the graceful exit for this model and enables us to...
We explore connections between two salient chaotic
features, namely Lyapunov exponent and butterfly velocity, for the class of asymptotically Lifshitz black hole background with arbitrary critical exponent by implementing three different holographic approaches, namely,
entanglement wedge method, out of time-ordered correlators (OTOC) and pole-skipping. We present a comparative study where...
Primordial black holes (PBHs), potentially formed in the early universe, may play a crucial role in cosmology, serving as seeds for supermassive black holes and contributing to the formation of merging black hole binaries observed by LIGO/VIRGO. They have also been proposed as candidates for dark matter. Another scenario involves cosmic strings, hypothetical linear defects predicted by various...
In the post-inflationary scenario, if PQ symmetry breaking occurs, a network of global cosmic strings are expected to form. At the time of the QCD phase transition, the previously scaling network of such defects will collapse by forming domain walls attached to strings. Given that all of the energy density of the string network is left behind into axion waves, in order to improve current...
The bulk action of the Yang-Mills theory based on the compact Lorentz group Spin(4)=SU(2)xSU(2) is determined by one parameter c_T. When c_T=1, the theory is right-handed and predicts a spin-2 field with the dynamics of the metric tensor in general relativity in the presence of dust. When c_T=0, the theory is achiral and has no local degrees of freedom. A transition from the latter to the...
