Event Time:
Monday, May 13, 2024 | 12:30 pm - 2:30 pm
Event Location:
TRIUMF Theory Room, 4004 Wesbrook Mall and zoom; https://ubc.zoom.us/j/68938408525?pwd=MVBBK05ZQWdCK2tJKzNGUXZaazJhdz09 Passcode: 959424
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2024-05-13T12:30:00
2024-05-13T14:30:00
Probing Beyond Standard Model Physics Through Ab Initio Calculations of Exotic Weak Processes in Atomic Nuclei
Event Information:
"Exotic weak decays offer a unique way to probe physics beyond the Standard Model in a low-energy regime using the atomic nucleus as a window to complement the high-energy searches done at particle accelerator facilities. However, in order to extract the relevant physics parameters from experimental observations, inputs from nuclear theory are required.
The hypothetical neutrinoless double beta decay has gathered a lot of interest, as its observation would answer many standing questions in particle physics. First, it would unveil fundamental properties of the most abundant yet most elusive massive particle: the neutrino. A simple observation of this decay would imply the neutrino to be Majorana, meaning that it is its own antiparticle, as well as give insight into its absolute mass. Furthermore, the existence of this decay would explain the matter/antimatter asymmetry of the universe.
In order to extract the neutrino mass and potential couplings to more exotic mechanisms, as well as compare sensitivities of experiments using different isotopes, the nuclear matrix element must be obtained from nuclear theory. Unfortunately, the different models that have historically been used to compute this quantity have shown a large spread with no means of quantifying their respective uncertainties, greatly hindering the experimental precision.
In this thesis, we use recent advances in ab initio methods, which profit from the rapid increase in computational power to calculate nuclear observables directly from the interaction between the nucleons. In particular, we use the ab initio valence-space in medium similarity renormalization group method to compute the matrix element of all relevant candidate isotopes for experimental searches. We further develop a new machine learning emulator that greatly increases the speed of calculations. Using this emulator, we probe the full input parameter space of the calculation to give the first statistical uncertainty on the matrix element.
Our results show smaller values than previous models and are consistent with other ab initio methods. This provides a much tighter constraint than the spread coming from previous models, greatly clarifying the picture for both current and future experimental searches of the decay. “
Event Location:
TRIUMF Theory Room, 4004 Wesbrook Mall and zoom; https://ubc.zoom.us/j/68938408525?pwd=MVBBK05ZQWdCK2tJKzNGUXZaazJhdz09 Passcode: 959424
Event Time:
Friday, May 24, 2024 | 10:00 am - 12:00 pm
Event Location:
Henn 318
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2024-05-24T10:00:00
2024-05-24T12:00:00
Negative Lambda Quantum Cosmology
Event Information:
Abstract: We present a model of quantum cosmology based on anti-de Sitter/conformal field theory (AdS/CFT) holography. The spacetimes in our construction are time-symmetric, big-bang/big-crunch cosmologies with a negative cosmological constant $\Lambda$. In the simplest version of our model the cosmology lives inside a spatially finite bubble within an otherwise empty AdS spacetime. By studying the thermodynamic and geometric properties of this spacetime, we provide evidence that the ``bubble of cosmology'' spacetime has a well-defined dual CFT description.
It is also desirable to have a cosmology which is globally homogeneous and isotropic. We present an upgraded model in which this is the case.
Although a homogeneous cosmology is not asymptotically AdS and hence cannot be described directly by AdS/CFT, the time-reflection symmetry of the spacetime allows us to perform an analytic continuation, following which the spacetime is an asymptotically AdS Euclidean wormhole. If we assume that the cosmology is spatially flat a second analytic continuation obtains a Lorentzian traversable AdS wormhole. The AdS wormhole spacetimes can be described using holography: they are dual to a pair of three-dimensional CFTs coupled via a four-dimensional theory.
We explain how an anomalously large amount of negative energy can support the traversable wormhole, and we begin to populate the holographic dictionary relating observables in the wormhole/cosmology to observables in the microscopic theory. Finally we show that time-dependent scalar fields naturally enable these cosmologies to contain a period of accelerated expansion, suggesting that our $\Lambda<0$ models could ultimately provide the framework for a fully microscopic description of our universe.
Event Location:
Henn 318