# Looking for Dark Energy where it cannot hide

**Project Level:** Winter

**Project Duration: **

Four weeks, 20 hours per week. Applicants must be on-site for at least 4

hours a week.

**Description:**

The discovery of the accelerated expansion of the Universe challenged our understanding of gravitational interaction as an attractive force. Our

ignorance about the source of this acceleration is reflected by the name we use to refer to it: Dark Energy. The most observationally successful

candidate for Dark Energy is a cosmological constant which, by definition, has the same (constant) behaviour at all scales. On the other hand, the

value inferred from cosmological observations for this constant makes its physical interpretation challenging. From the gravitational point of view,

we expect an effective cosmological constant to arise from the quantum fluctuations of the vacuum spacetime. However, the standard model of

particle physics predicts the value of these fluctuations to be several orders of magnitudes larger than the observed cosmological one. For this

reason, many alternative models of Dark Energy have been proposed during the past 20 years, which behave similarly to a cosmological constant

on sufficiently large scales but have entirely different dynamics at smaller ones.

The successful applicant will study how a general dynamical Dark Energy affects physics at smaller scales in this project. In particular, Dark Energy

might influence the formation and distribution of Large-Scale Structure in the Universe and the dynamics on solar-system scales. This will require the applicant to study and apply cosmological perturbation theory in linear and non-linear regimes.

**Expected Outcomes:**

The applicant will have the opportunity to study fundamental tools of modern cosmology, such as cosmological perturbation theory and

statistical analysis of Large-Scale Structure. They will also have a chance to apply those tools to alternative Dark Energy candidates and have an

opportunity to generate publications from their research. They are also expected to present the conclusions of their study in the form of an oral

presentation or a report at the end of their project. Along the way they will develop statistical and mathematical skills as well as programming skills, which are applicable to many fields.

**Suitable for:**

This project is open to applications from 3rd – 4th year students only. Ideally, the applicant will have an interest in General Relativity and Astrophysics, even though a previous background in these topics is not required.

**Further Information:**

For further information on the project, please contact Dr Leonardo Giani.