Neutrino Mass Explains Dark Matter and Matter-Antimatter Asymmetry

Key Quotes

"Modern physicists have no such scruples, of course, but more importantly neutrinos turn out to be very detectable, given sufficient resources and experimental technique."

Sean Carroll introduces the concept of neutrinos by contrasting historical hesitancy to propose undetectable particles with the modern ability to detect them. This highlights the evolution of experimental capabilities in physics.

"The idea of the neutrino was proposed around 1930 by Wolfgang Pauli because there was this known phenomenon namely beta decay... but there's a couple of things that weren't quite working out about that idea... so there was what by modern standards was a perfectly obvious thing to do propose a new invisible particle that carried away a little bit of the spin and a little bit of the energy but in 1930 that was just not done so Wolfgang Pauli eventually did it he proposed there was a little particle but he was embarrassed to do so he was like sorry you know maybe it's an idea don't take it too seriously"

Sean Carroll explains the historical context of the neutrino's proposal, emphasizing that it was a theoretical necessity to explain experimental discrepancies in beta decay. Pauli's embarrassment underscores the difficulty and unconventional nature of hypothesizing such a particle at the time.

"Ryan Patterson received his Ph.D. in physics from Princeton University. He is currently Professor of Physics at Caltech. His research involves a number of aspects of experimental neutrino physics, including involvement in the NOvA and DUNE experiments."

This biographical information establishes Ryan Patterson's expertise and credentials in experimental neutrino physics. It grounds his subsequent explanations in his direct involvement with leading neutrino research projects.

"The electron is electrically charged... the strong force of nature... and then there is a third force called the weak force... so the electron is electrically charged it's also charged under the weak force... the um nuclear material with the protons and neutrons they're experiencing the strong force as well as the electrical force as well as the weak force so they experience all three so now we get to neutrinos neutrinos only experience the weak force so they only get this very weak version of the interactions we have in the standard model and that leads to what as you were saying that they pass right through things almost never interacting"

Ryan Patterson clarifies the fundamental forces and particle interactions. He explains that neutrinos uniquely interact only via the weak force, which accounts for their elusive nature and ability to pass through matter unimpeded.

"The electron also has a partner in the same way and that partner is the neutrino so the electron has a a so called electron neutrino that goes with it and just that prefix that electron neutrino is just how we tell which neutrino we're talking about that's associated with the electron so with the quarks and their colorful names there are also heavier versions of the electron the electron is the familiar one of those electrically charged particles that we have in our atoms there's also a muon and because it's heavier it is able to decay to its lighter cousin to its electron cousin and it does that very quickly and so we don't see them around in our everyday life... but in any case those muons don't stick around they they decay away and you just have electrons left and then there's a heavier one still called the tau particle all three of those have an associated neutrino an electron neutrino a muon neutrino and a tau neutrino"

Ryan Patterson details the "family structure" of fundamental particles, explaining that each charged lepton (electron, muon, tau) has a corresponding neutrino flavor. This illustrates the organized, yet complex, nature of particle families within the Standard Model.

"The idea that particles feel certain forces and not others maybe isn't perfectly obvious you know the i guess people are comfortable with the idea that some objects are electrically neutral and therefore don't feel electromagnetism but it's also like that for other forces and and the neutrino only feels the weakest one i think it's a very good way to sort of conceptualize it"

Sean Carroll reflects on the conceptualization of particle interactions, noting that the idea of particles interacting with only specific forces, like neutrinos with only the weak force, might not be immediately intuitive. He validates Patterson's explanation as a helpful way to understand this.

"The ordering of the masses is something we need to know if we shoot our neutrinos through hundreds or thousands of miles of earth's crust those neutrinos experience the presence of all of that stuff that they're traveling through they're not directly interacting with it and pointing off in a different direction but the very presence of all of that stuff and in particular all the electrons on their route to the detector modifies the oscillations that we're going to try to measure and the higher the energy the neutrino the farther we're going to be shooting it and the more all this matter matters and it is through that phenomenon that we can try to determine the ordering of the neutrino masses"

Ryan Patterson explains how the mass ordering of neutrinos can be determined. He describes how the presence of matter, specifically electrons, along the neutrino's path can influence their oscillations, and this effect is measurable and dependent on neutrino energy and distance.