Speaker: Takemichi Okui
Title: Monopole-Fermion Scattering and the Solution to the Semiton/Unitarity Puzzle
Room: 3024
Host: John Terning
Abstract: The talk will cover my recent work on the so-called semiton/unitarity puzzle in monopole-fermion scattering. Traditionally it was thought such scattering could lead to fractional particle numbers (hence "semitons"), but there are no such states in the Fock space of the theory (hence "unitarity" problem). I will discuss how this problem is solved in Polchinski's "fermion-rotor system", which is an accurate description of charged massless fermions scattering on a magnetic monopole core in the limit of zero gauge coupling.
User:
High-Energy Seminars
Time:
4:00pm - 6:00pm
Location:
PHY 285
Send Reminder:
Yes - 20241002
Description:
Title: Probing Fundamental Theories & Reheating Cosmology with Cosmic Millicharge Background
Abstract: Exploring millicharged particles (particles with small rational or irrational charges) has become a central focus in contemporary particle physics and cosmology. Linked to charge quantization, which spurred Dirac Quantization and Grand Unification Theories, the millicharge searches are also a testing grounds for string theory and quantum gravity. I will give a general introduction to millicharged particles and present a novel approach to leverage them for probing reheating cosmology—a pivotal phase post-inflation, shaping the current Universe's particle composition. Millicharge searches offer insights into reheating scenarios and temperatures. I will also discuss the irreducible cosmic millicharged background and implications on the dark matter observations, the 21-cm absorption spectrums, Big Bang nucleosynthesis, and CMB measurements.
Finally, the talk delves into dedicated experimental efforts, notably the FORMOSA experiment at CERN, LANSCE-mQ at LANL, and neutrino experiments at Fermilab, which may help unveil the mysteries in cosmology and fundamental theories.
Speaker: Yu-Dai Tsai (LANL)
Host: Matthew Citron
User:
High-Energy Seminars
Time:
1:30pm - 3:00pm
Send Reminder:
Yes - 0 days 6 hour 0 minutes before start
Description:
Speaker: Rodolfo Capdevilla
Title: Road to Minimal WIMPs
Room: 3024
Host: John Terning
Abstract: Minimal Dark Matter (MDM) models extend the Standard Model (SM) by introducing an electroweak multiplet, whose neutral component $\chi_0$ serves as a dark matter (DM) candidate. The multiplet can be a doublet (Higgsino-like), triplet (Wino-like), and beyond. Direct Detection (DD) and Indirect Detection (ID) searches can probe significant portions of the parameter space in these models, particularly under the assumption that $\chi_0$ accounts for 100% of the DM in the universe (the thermal target). Collider searches aim to produce the charged members of the multiplet, $\chi^+$, which then decay into $\chi_0$ and a charged SM particle. These searches are more effective when $\chi_0$ accounts for a fraction of the DM in the universe, as this leads to a lower mass multiplet compared to the thermal target, increasing the production cross sections. This creates an interesting complementarity between DD, ID, and collider searches. In this talk, I discuss the role that present and future colliders can play in discovering MDM. Specifically, I show how a muon collider with just 3 TeV of energy can discover the elusive Higgsino-like state up to its thermal target using a Soft Track search. As the collider energy increases, larger multiplets become accessible. A 10 TeV muon collider could discover the Wino-like state up to its thermal target by searching for Disappearing Tracks (DT). Finally, DT searches at a 10 TeV muon collider can probe quintuplet masses up to 10% of the thermal target. These results indicate an interesting path ahead towards the discovery of the long standing minimal WIMP models.
User:
High-Energy Seminars
Time:
1:30pm - 3:00pm
Send Reminder:
Yes - 0 days 6 hour 0 minutes before start
Description:
Speaker: Anson Hook
Title: Dyonic Bound States
Room: 3024
Host: John Terning
Abstract: We study (multi) fermion - monopole bound states, many of which are the states that dyons adiabatically transition into as fermions become light. The properties of these bound states depend critically on the UV symmetries preserved by the fermion mass terms, their relative size, and the value of θ. Depending on the relative size of the mass terms and the value of θ, the bound states can undergo phase transitions as well as transition from being stable to unstable. In some simple situations, the bound state solution can be related to the Witten effect of another theory with fewer fermions and larger gauge coupling. These bound states are a result of mass terms and symmetry breaking boundary conditions at the monopole core and, consequently, these bound states do not necessarily have definite quantum numbers under accidental IR symmetries. Additionally, they have binding energies that are O(1) times the fermion mass and bound state radii of order their inverse mass. As the massless limit is approached, the bound state radii approach infinity, and they become new asymptotic states with odd quantum numbers giving a dynamical understanding to the origin of semitons.
User:
High-Energy Seminars
Time:
1:30pm - 3:00pm
Send Reminder:
Yes - 0 days 6 hour 0 minutes before start
Description:
Speaker: Max Ruhdorfer
Title: Physics Potential of Forward Muons at a Muon Collider
Room: 3024
Host: John Terning
Abstract: In this talk I explore the physics potential of forward muon detection at muon colliders for probing neutral
effective vector boson production across various kinematic regimes. Vectors with relatively low energy
produce the Higgs boson and the extended muon angular coverage enables studies of the Higgs properties,
such as the measurement of the total production cross section and of the branching ratio to invisible final states.
New heavy particles could be produced by vectors of higher energy, through Higgs portal interactions.
If the new particles are invisible, the detection of the forward muons is essential in order to search for this
scenario. The angular correlations of the forward muons are sensitive to the quantum interference between
the vector boson helicity amplitudes and can be exploited for the characterisation of vector boson scattering and
fusion processes. This is illustrated by analysing the CP properties of the Higgs coupling to the Z boson. Our
findings establish a compelling physics case and provide benchmarks for the design of a specialized forward muon detector.
