Theoretical Particle Cosmology

Theoretical Particle Cosmology

Group Members

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Research Activity

Modern theoretical cosmology is concerned with the application of new theories of particle physics and gravitation. These theories help us to understand the evolution of the Universe from the earliest time to the present day. There are two essential reasons for doing this:

  • to understand the Universe we observe around us today
  • to test new particle physics theories and gravity theories against observation

Astroparticle Physics (also known as Particle Cosmology) relies on the fact that different theories make different predictions about the evolution of the Universe and therefore about the present-day state of the Universe. One in effect uses the Universe as a 'cosmic collider', with the telescopes used by astronomers and underground experiments used to detect dark matter playing the role of the particle detectors of collider experiments. The results of Astroparticle Physics complement those of colliders such as the CERN Large Hadron Collider. The 'cosmic collider' reaches energies vastly more extensive than those that can be reached by any collider on Earth.

Lancaster has been at the leading edge of research in theoretical cosmology and astroparticle physics since it became an established field in the early 1980s.

A significant part of our research is on the origin and nature of the primordial density perturbation. This serves as the 'seed' for the cosmic microwave background temperature fluctuations and the large-scale cosmological structures we can observe today. The group has made outstanding contributions to inflation theory. This theory accounts for the primordial density perturbation, in particular, the development of scalar and vector inflation and curvaton models, inflation models based on weakly-interacting dark matter particles, and supersymmetric inflation models.

We have also made fundamental contributions to:

  • dark matter and baryogenesis
  • the cosmology of supersymmetric particle theories
  • Q-balls in supersymmetric cosmology
  • primordial magnetic fields
  • many other topics in modern cosmology and astroparticle physics

Key Research

  • Inflation Theory and Primordial Perturbations
  • Scalar and Vector Curvaton Theory
  • Dark Matter and Baryogenesis
  • Cosmology of Supersymmetry

PhD Projects

  • Cosmic Inflation in the early Universe

    Project Supervisor

    Dr Konstantinos Dimopoulos

    Description

    Cosmic Inflation is a period of superluminal expansion of space just after the Big Bang. It is fixing the initial conditions of the Universe history, in that it makes the Universe large and uniform. Additionally, inflation generates quantum-mechanically the controlled violation of uniformity necessary for the build-up of structures such as galaxies and galactic clusters.

    Inflation is under new light due to the recent cosmological data, such as the Planck CMB observations. Several families of inflationary models are now excluded, while new research on the favoured models overlaps with concerns over the stability of the electroweak vacuum (Higgs inflation) and the UV completion of gravity (R^2 inflation). The discovery of gravitational waves has ignited new interest in detecting primordial gravitational waves, quantum generated during inflation, which is a smoking gun for inflation theory, and motivates forthcoming missions (e.g. POLARBEAR).

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  • Quintessential Inflation and Dark Energy

    Project Supervisor

    Dr Konstantinos Dimopoulos

    Description

    Observations suggest that the Universe at present is engaging anew in a period of late time inflation, determined by a mysterious substance called dark energy, which makes up about 70% of the density budget of the Universe today. Dark energy can be modelled similarly to primordial inflation, through a substance called quintessence.

    Quintessential inflation is the effort to economically treat dark energy and primordial inflation in a common theoretical framework. As such, quintessential inflation connects not only with primordial inflation data but also with imminent future dark energy observations (e.g. EUCLID), which can provide information on early Universe physics at very high energies, well beyond the reach of Earth-based experiments. Moreover, quintessential inflation can exploit the famous scale mystery, whereby the scale of electroweak physics, which is explored in collider experiments such as the LHC, is roughly the geometric mean of the Planck energy scale, which is associated with gravity, and the dark energy scale. This implies that observations in the early and late Universe can be used to shed some light on particle physics phenomenology.

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  • Inflation, Dark Matter and Dark Energy in Theories Beyond of the Standard Model of Particle Physics

    Project Supervisor

    Dr John McDonald

    Description

    The Standard Model of particle physics is unable to account for a range of cosmology and phenomenology, including inflation, the nature of dark matter, the nature of dark energy, the matter-antimatter asymmetry (baryon asymmetry) and the absence of strong CP violation. In this project, you will explore plausible extensions of the Standard Model that will attempt to simultaneously account for these issues.

    Inflation can be achieved in conventional particle physics theories if the scalar particle driving inflation (the "inflation") is non-minimally coupled to gravity. You will study non-minimally coupled inflation models, in both conventional General Relativity (metric formulation) and in alternative frameworks (such as the Palantini formulation), which are rooted in plausible particle physics theories. You will study the cosmological evolution of the models from inflation through reheating to the present time. The possibility of accounting for dark matter, dark energy and the baryon asymmetry will be explored.

    My present programme is focused on the QCD axion model, which can account for both inflation and dark matter, as well as providing a solution to the strong CP problem. With my present PhD student, Amy Lloyd-Stubbs, we are studying in detail the cosmological possibilities of the QCD axion model, including inflation, dark matter and dark energy. This has recently produced a first paper ["The KSVZ Axion Model with Quasi-Degenerate Minima: A Unified Model for Dark Matter and Dark Energy", A.Lloyd-Stubbs and J.McDonald, arXiv:1807.00778, to be published in Physical Review D.]

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  • The Cosmology and Phenomenology of Clockwork Models of Particle Physics

    Project Supervisor

    Dr John McDonald

    Description

    Clockwork models of particle physics are based on a specific structure of explicit symmetry breaking which can generate particles with hierarchically small masses and interaction strengths. Such weakly coupled and low mass particles have a range of applications in cosmology, for example as stable or long-lived dark matter particles or weakly-coupled inflations to drive inflation. In this project, you will explore the possible applications of the Clockwork mechanism to cosmology and particle phenomenology. My recent work in this area has focused on its application to dark matter particles produced by a process known as Freeze-In.

    [Publications: "A Clockwork Higgs Portal Model for Freeze-In Dark Matter", J.Kim and J.McDonald, arXiv:1709.04105 [hep-ph], Phys.Rev. D98 (2018) 023533; "Freeze-In Dark Matter from a sub-Higgs Mass Clockwork Sector via the Higgs Portal", J.Kim and J.McDonald, arXiv:1804.02661, to be published in Phys.Rev.D.]

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  • Cosmology as a Relational Dynamical System

    Project Supervisor

    Dr David Sloan

    Description

    Cosmology models the behaviour of our universe in terms of a small set of descriptive variables; the scale factor, Hubble parameter, relative shear expansions etc. From Einstein’s equations, we can calculate the equations of motion of these systems and find their evolution. The complete behaviour can be described in terms of dynamical systems arising from a Hamiltonian and expressed as a flow on phase space. All these descriptions rely upon factors which cannot be explicitly measured by an observer within the universe at all times. In recent work, I have shown that under certain conditions these can be extended beyond the initial singularity. One key aspect of your project will be to examine the nature of singularities in relational systems.

    The goal of this project will be to develop a complete description of cosmological systems which relies only upon relational measurements and find their cosmological completions. You will develop skills in differential geometry (particularly symplectic geometry) and numerical methods alongside a strong understanding of physical systems. You will gain significant insight into the nature of singularities in general relativity and the geometry of mathematical physics.

    The Physics Department is the holder of an Athena SWAN Silver award and JUNO Championship status and is strongly committed to fostering diversity within its community as a source of excellence, cultural enrichment, and social strength. We welcome those who would contribute to the further diversification of our department.

     

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Postgraduate Training

The theoretical particle cosmology group offers specific training as well as supporting our students to attend other training courses in the department and to attend summer schools and other retreats.

Training

  • Particle Cosmology Directed Reading Programme - Dr K Dimopoulos/Dr J McDonald
  • Relativistic Quantum Mechanics/Quantum Electrodynamics – Dr R Henderson
  • Quantum Field Theory - Dr R Henderson
  • Introduction to Probability and Statistics for EPP - Dr A Blake

Summer Schools

Cosmology students attend the British Universities Summer School in Theoretical Elementary Particle Physics (BUSSTEPP) at the end of their first year of studies. They also attend the annual Young Experimentalists and Theorists Institute (YETI) at Durham and regular UK Cosmology workshops. All of our students will have the opportunity to take part in international conferences.