Research

“There’s something that doesn’t make sense. Let’s go and poke it with a stick.”

– The Doctor

Image Credits: ESA & Planck Collaboration

My research encompasses several different themes, but the overarching link is dark matter. Broadly speaking, my work lies at the interface between cosmology and particle physics: I try to find mappings between the underlying dark matter phenomenology and its impact on cosmological observables, in order to understand the fascinating mystery that is dark matter. Some of my work also branches out to other topics that are only partially connected to dark matter. Below you can find a brief summary of my main research areas.

Non-cold dark matter models

Histogram of S8 highlighting how Cannibal Dark Matter is closer to the weak lensing measurements than LCDM.
Histograms showing the marginalised S8 posteriors for three different Cannibal dark matter models compared to ΛCDM and the latest weak lensing result. Source: S. Heimersheim et al. 2008.08486.

I have studied the cosmological implications of non-cold dark matter models, such as dark matter with different interactions, dark matter with cannibalistic number changing processes, and dark matter produced by the evaporation of primordial black holes. Using data such as CMB, BAO, and Lyman-α I have put state-of-the-art constraints on several of these interacting scenarios. Together with collaborators in Aachen and Cambridge, we also showed that Cannibalistic dark matter could help address the S8 tension.

Lyman-α data

In order to make use of Lyman-α data to constrain the aforementioned models, I have developed a new technique that does not require new computationally expensive N-body simulations. The approach instead relies on using a pre-existing grid of simulations covering a broad class of models, which we can interpolate in to get robust bounds from Lyman-α data. With collaborators in Aachen and Trieste, we showed the validity of this approach for dark matter interacting with dark radiation. We are currently expanding this method to cover many more dark matter interactions and other non-cold dark matter models.

Plot showing the two sigma exclusion bound for Dark Matter - Dark Radiation interactions, highlighting how much Lyman-alpha data improves these bounds.
Dark matter – dark radiation interactions: two-dimensional posterior distributions for the interaction strength, amount of dark radiation, H0, and σ8. The light blue area shows the region where our Lyman-α method can be applied. Source: M. Archidiacono, D. C. Hooper, et al. 1907.01496.

Cosmological tensions

Plot showing the evolution of the Hubble parameter in the late universe, highlighting how Dark Matter - Dark Energy interactions cannot account for all the data points.
Bestfit late-time evolution of H(z) for dark matter – dark energy interactions using different datasets. For comparison, the standard ΛCDM prediction is also shown in black. Source: M. Lucca & D. C. Hooper 2002.06127.

I have also analysed the possibility that these non-cold dark matter models might be able to address the cosmological tensions. I verified that some models of dark matter – dark radiation interactions can simultaneously alleviate the H0 and S8 tensions; however, the further addition of BAO+BBN or supernovae data would likely rule out this solution. On the other hand, together with a collaborator in Brussels, we showed that dark matter – dark energy interactions do not appear to solve the tension, especially when incorporating probes such as BAO and Pantheon.

Forecasts

I have forecasted the constraining power of future cosmological data, such as from spectral distortions or galaxy lensing surveys. This led me to develop mock likelihoods for different missions (LiteBIRD, CMB-S4, PICO, PIXIE, PRISM), which I then used to forecast the constraints we can expect in the future for the sum of neutrino masses, decaying dark matter, and primordial black hole evaporation. With collaborators in Aachen and Manchester, we have shown that future spectral distortions missions offer a great complementarity with current and future CMB anisotropy missions.

Plot showing the excluded regions for decaying Dark Matter, highlighting that spectral distortion missions will offer several orders of magnitude improvement.
Forecasted exclusion regions (95% CL) on the decaying dark matter fraction as function of the particle lifetime for different combinations of current and future CMB spectral distortions and anisotropy missions. Source: M. Lucca et al. 1910.04619.

Inflation

Plot showing the allowed shape of the inflaton potential when Taylor expanded to order two, three, or four.
Representative sample of the inflaton potentials allowed by Planck+BK15, when the potential is Taylor-expanded to order n under the assumption of N∗ = 55 e-folds of inflation. Source: Y. Akrami et al. 1807.06211.

During my Master’s thesis, I implemented an efficient treatment of axion monodromy inflation in CLASS. This later led me to join the Planck collaboration during my PhD, where I looked for hints in the latest data for this model. I also performed various reconstructions of the Taylor-expanded inflationary potential, both with and without slow-roll assumptions. The results I obtained were included in the Planck 2018 Inflation paper.

Coding

In order to study these different scenarios, I have implemented most of these dark matter models in the cosmology code CLASS. Additionally, the forecasts relied on the parameter inference code MontePython. This has led me to become an active developer and contributor of both of these codes.

%d bloggers like this: