Particle Physics

New physics in the neutrino sector might be necessary to address anomalies between different neutrino oscillation experiments. Intriguingly, it also offers a possible solution to the discrepant cosmological measurements of H_0. 
We show here that delaying the onset of neutrino free-streaming until close to the epoch of matter-radiation equality can naturally accommodate a larger value for the Hubble constant, while not degrading the fit to the cosmic microwave background (CMB) damping tail. We achieve this by introducing neutrino self-interactions in the presence of a non-vanishing sum of neutrino masses. This "strongly interacting" neutrino cosmology prefers a 3+1 neutrino scenario, which has interesting implications for particle model-building and neutrino oscillation anomalies. Due to their impact on the evolution of the gravitational potential at early times, self-interacting neutrinos and their subsequent decoupling leave a tell-tale structure on the matter power spectrum. 
Our analysis shows that it is possible to find radically different cosmological models that nonetheless provide excellent fits to the data, hence providing an impetus to thoroughly explore alternate cosmological scenarios.

The n-point correlation functions (n>2) of primordial fluctuations, known as primordial non-Gaussianities, encode rich information about the physical degrees of freedom and their interactions at inflation scale, and can be viewed as signals from a cosmological collider with huge energy. In this talk we introduce recent theoretical attempts to extract new physics at the inflation scale from primordial non-Gaussianities, including possible discovery channels, the background signals from the standard model, and signals from new physics such as heavy neutrinos, and a possible way to turn inflation into a Higgs collider.

We present the complete history of structure formation in a simple dissipative dark-sector model. The model has only two particles: a dark electron and a dark photon. Dark-electron perturbations grow from primordial overdensities, become non-linear, and form dense, dark galaxies. We show that asymmetric dark stars and black holes form within the Milky Way from the collapse of dark electrons. These exotic compact objects may be detected and their properties measured at new high-precision astronomical observatories, giving insight into the particle nature of the dark sector without the requirement of non-gravitational interactions with the visible sector.

In this talk, I will detail two ways to search for low-mass axion dark matter using cosmic microwave background (CMB) polarization measurements. These appear, in particular, to be some of the most promising ways to directly detect fuzzy dark matter. Axion dark matter causes rotation of the polarization of light passing through it. This gives rise to two novel phenomena in the CMB. First, the late-time oscillations of the axion field today cause the CMB polarization to oscillate in phase across the entire sky. Second, the early-time oscillations of the axion field wash out the polarization produced at last-scattering, reducing the polarized fraction (TE and EE power spectra) compared to the standard prediction. Since the axion field is oscillating, the common (static) ‘cosmic birefringence’ search is not appropriate for axion dark matter. These two phenomena can be used to search for axion dark matter at the lighter end of the mass range, with a reach several orders of magnitude beyond current constraints. I will present a limit from the washout effect using existing Planck results, and discuss the significant future discovery potential for CMB detectors searching in particular for the oscillating effect.

[1903.02666]

For thousands of years, astronomy was restricted to what we could see with our eyes. But visible light makes up only a tiny fraction of a spectrum emitted by celestial objects.

We now know that light is not the universe’s sole means to reveal the mysteries of the heavens. Until recently, we simply lacked the windows through which to view these aspects of our universe.

Over the last few decades, astronomers have revolutionized our windows on the universe with telescopes of unprecedented sensitivity to light beyond what we can see with our eyes.

Observatories now allow us to see ghostly particles called neutrinos, and ripples in the fabric of space itself - called gravitational waves.

In his Perimeter Public Lecture on April 3, 2019, Chad Hanna will describe how these new windows have changed our view of the cosmos and explore what new wonders may be unveiled in the decades to come.

Hanna is an associate professor at Pennsylvania State University. His research focuses on studying the universe with gravitational waves using the Laser Interferometer Gravitational-Wave Observatory (LIGO).

Hanna and his research group work to enable multi-messenger astronomy through gravitational wave observations of merging neutron stars and black holes. Prior to joining Penn State, he was a senior postdoctoral researcher at Perimeter Institute.

Bosonic ultra-light dark matter (ULDM) would form cored density distributions at the centres of galaxies. These cores admit analytic description as the lowest energy bound state solution ("soliton") of the Schrödinger-Poisson equations. Numerical simulations of ULDM galactic halos found empirical scaling relations between the mass of the large-scale host halo and the mass of the central soliton. 
We connect the simulation results of different groups to basic properties of the soliton. Importantly, simulations imply that the specific kinetic energy in the soliton and in the host halo should be approximately equal. This relation predicts that the peak circular velocity, measured for the host halo in the outskirts of the galaxy, should repeat itself in the central region. Contrasting this prediction to the measured rotation curves of low surface-brightness galaxies, we show that ULDM in the mass range m ~ 10⁻²²-10⁻²¹ eV, which has been invoked as a possible solution of small-scale puzzles of ΛCDM, is in tension with the data. We discuss the potential of detailed dynamical modelling of the Milky Way and other well-resolved galaxies to probe ULDM up to m ~ 10⁻¹⁹ eV.

The discovery of a Higgs like boson at LHC in 2012 was a development of fundamental importance in particle physics. With this newly discovered state included in theoretical predictions of scattering events,  the Standard Model can be extrapolated  to much higher experimental energies. This implies that a degree of scale separation will be present between the discovered particles of the Standard Model, and any new particles required to address the outstanding mysteries that the Standard Model leaves unanswered. As a result, interest in treating the Standard Model as a consistent Effective Field Theory (the SMEFT) has dramatically increased. This powerful theory is the state of the art in studying experimental results model independently, up to energies that LHC probes in a robust fashion experimentally. Rather remarkably, as interest in this theory has increased in recent years, a number of subtleties has also been discovered in the physics of the SMEFT.  In this talk, I will review this rapidly advancing area.

I will introduce my recent works on the phenomenology of solutions to the strong CP problem, QCD axion and Parity. I will first describe the production of the QCD axion in the early universe and show that the dark matter abundance is naturally reproduced for a wide range of the parameter space. I will then show a tight relation between the Parity solution, dark matter direct detection, the proton decay, and the precise measurements of the standard model parameters.

The 21st century may come to be known as the Age of Photonics, as we exploit our ability to make and manipulate light as an amazing carrier of energy and information. From quantum computing and entanglement to eye surgery and solar energy, humans are already reaping the benefits of our own endeavours to understand and control light.

In her public lecture webcast at Perimeter on March 6, Cather Simpson from the University of Auckland will highlight her research in exploring how recent advances in the physics of light are transforming our ability to feed the planet safely and sustainably.

Simpson moved from Case Western Reserve University in the USA to the University of Auckland’s Physics and Chemistry Departments in 2007. There, she started the Photon Factory, a laser centre whose mission is to exploit exotic, ultrashort pulsed lasers to enable cross-disciplinary research from the very fundamental to the applied and entrepreneurial.

Simpson’s research explores the interaction of light with matter, particularly how materials can convert light into more useful forms of energy. A relatively recent area of focus is in agriculture, where her work has led to two international award-winning spinout companies. Her many recent accolades include a National Tertiary Teaching Excellence Award, the 2016 Silicon Valley Forum 1st-place AgTech medal, and election as a Fellow of the Royal Society of New Zealand Te Apārangi.

Mirror sectors -- hidden sectors that are approximate copies of the Standard Model -- are a generic prediction of many models, notably the Mirror Twin Higgs model. Such models can have a rich cosmology and many interesting detection signatures beyond the realm of colliders. In this talk, I will focus on the possibility that mirror matter can form stars which undergo mirror nuclear fusion in their cores. I will discuss the mechanisms by which these objects can emit Standard Model light and estimate their luminosity and prospects for their detection.

The minimal Standard Model running of the gauge couplings gives us a hint of a Grand Unified Theory (GUT) at M_U ~ 10^14 GeV — a scale, however, too high to probe directly via collider searches. Fortunately, since the inflationary Hubble scale H can be as high as  5 x 10^13 GeV ~ M_U, such GUT scale states can be cosmologically produced during inflation and contribute to primordial non-Gaussianity (NG).

In this talk, I will explore the possibility of doing on-shell, mass-spin spectroscopy of GUT-states by studying such NG contributions in an extra-dimensional framework of orbifold GUTs. I will identify an interesting regime where the extra dimension is stabilized close to the onset of a horizon and find that the KK gravitons and KK gauge bosons can mediate observable NG providing a direct probe of orbifold GUTs.

Axion-like particles are a broad class of dark matter candidates which are expected to behave as a coherent, classical field with a weak coupling to photons. Research into the detectability of these particles with laser interferometers has recently revealed a number of promising experimental designs. Inspired by these ideas, we propose the Axion Detection with Birefringent Cavities (ADBC) experiment, a new axion interferometry concept using a cavity that exhibits birefringence between its two, linearly-polarized laser eigenmodes. This experimental concept overcomes several limitations of the designs currently in the literature, and can be practically realized in the form of a simple bowtie cavity with tunable mirror angles. Our design thereby increases the sensitivity to the axion-photon coupling over a wide range of axion masses.