TACOS 2026

22 Oct 2026, 18:00 → 24 Oct 2026, 20:30 America/Chicago

Kimberly Boddy (University of Texas at Austin), James Dent, Andrew Long (Rice University), Joel Meyers (Southern Methodist University), Kevin Kelly (Texas A&M University), Kevin Huffenberger (TAMU)

Theoretical Astroparticle and Cosmology Symposium in Texas

This meeting brings together researchers interested in topics at the intersection of theoretical particle physics, astrophysics, and cosmology. Participants from various institutions in Texas present and discuss the latest developments in their subfields, with the aim of fostering ideas and collaborations among faculty, postdocs, and graduate students. The host institution rotates from year to year to enable interactions with local experts in neighboring subfields.

This year we are at Texas A&M University and the main meeting website is: https://sites.google.com/view/texas-tacos/home

Location

All talks are in the Hawking Auditorium of the Mitchell Institute for Fundamental Physics & Astronomy (except for the Thursday evening Nobel lecture).

Scientific Organizing Committee:

Kimberly Boddy (UT Austin)
James Dent (Sam Houston)
Kevin Huffenberger (Texas A&M University)
Kevin Kelly (Texas A&M University)
Andrew Long (Rice)
Joel Meyers (SMU)

Thursday 22 October

Hagler Institute Nobel Lecture

1 The Universe From Beginning to End

Dr. Brian Schmidt, renowned astrophysicist and Nobel Prize winner, will present on his team’s discovery that the expansion of our universe is accelerating, a finding that changed our understanding of the universe by showing that about 70 percent of the universe’s mass is “dark energy.”

Dr. Brian Schmidt is an American Australian astrophysicist at the Australian National University’s Mount Stromlo Observatory and Research School of Astronomy and Astrophysics. In 2011, Schmidt and his team were awarded the Nobel Prize in Physics with their discovery that the expansion of our universe is accelerating. This scientific finding changed our understanding of the universe by showing that about 70 percent of the universe’s mass is in a previously unknown form, now usually referred to as “dark energy.”

Reception immediately following the lecture

This program is free and open to the public. Organized independently from TACOS.

Special location: Annenberg Presidential Conference Center

Registration is requested.

Speaker: Brian Schmidt (Australian National University)

Location

Registration link

Friday 23 October

08:00 Coffee, juice, and breakfast

Friday Morning

Convener: Kevin Kelly (Texas A&M University)

2 Welcome & Introduction

Speaker: Kevin Kelly (Texas A&M University)

3 The onset of light and darkness in the universe

Speaker: Prof. Steve Finkelstein (UT Austin)

4 Heavy Seeds and the Multi-scale Fueling of Early Supermassive Black Holes and Little Red Dots

The formation of supermassive black holes (SMBHs) in the early Universe has been a longstanding mystery due to the brief period available to assemble them. More recently, the unexpected discovery with the JWST of Little Red Dots (LRDs) has accentuated this challenge. Cosmological simulations investigating SMBHs confront the limitation that the compact scale of SMBH/LRD physics cannot be simultaneously resolved with the larger-scale cosmological environment. We address this limitation by selecting a targeted region around an SMBH seed from a cosmological parent simulation and re-running the region at higher resolution. We explore two SMBH formation scenarios: the standard, light seed stellar-remnant case, and the heavy-seed, direct collapse black hole (DCBH) channel. With the high-resolution achieved by the cutouts, we find that the DCBH is able to induce a buildup of high density gas nearby and grow in bursts of super-Eddington phases, producing an LRD-like spectrum. In contrast, the stellar remnant cannot do so and remains dormant, unable to affect the nearby gas or significantly evolve by gas accretion alone.

Speaker: Junehyoung Jeon (UT Austin)

5 Talkitos

10:40 Coffee Break

Friday Morning: Friday Morning 2

Convener: Joel Meyers (Southern Methodist University)

6 Talkitos

7 TBD -- Vasily Kokorev

8 TBD -- Alessandra Venditti

9 Talkitos

10 Group Photo

12:30 Lunch

Friday Afternoon: Friday Afternoon 1

Convener: Kimberly Boddy (University of Texas at Austin)

11 Talkitos

12 Search for Dark Matter in an Extended Nuclear Recoil Energy Window with LUX-ZEPLIN -- Dan Hunt

LUX-ZEPLIN (LZ) is a 7-tonne dual-phase xenon time projection chamber, located at the Sanford Underground Research Facility in Lead, South Dakota. While LZ typically searches for low-energy nuclear recoils indicative of a spin-independent WIMP, an extended nuclear recoil energy window up to ~270 keV enables searches for alternative models of dark matter, where low-energy recoils are suppressed. Recent analysis of 2.84 tonne-years of data resulted in the observation of one event consistent with a ~248 keV nuclear recoil, in tension with the background-only hypothesis at a global significance of 2.6σ. This talk presents an experimental overview of the extended-window analysis, including background modelling, rare background topologies, and prospects for a definitive explanation of this event of interest.

Speaker: Dan Hunt (University of Texas at Austin)

13 Producing the GeV Galactic Center Excess via Cosmic Ray-Dark Matter Scattering

The Fermi Large Area Telescope (Fermi-LAT) has observed a gamma-ray excess from the Galactic Center (GC) with the energy spectrum peaked around ∼ 2 GeV, commonly referred to as the Galactic Center GeV Excess (GCE). This excess has been persistent for 17 years, with possible explanations including dark matter (DM) annihilation and unresolved millisecond pulsars. In this pursuit to explain GCE, we propose a novel mechanism for generating gamma rays from the GC via cosmic-ray scattering off sub-GeV DM in the Milky Way halo. In this analysis, we investigate two DM models: (a) an inelastic DM model where the lighter DM is up-scattered to a heavier
DM, followed by its subsequent decay producing photons in the final state, and (b) an elastic DM model producing photons in the final state via a 2 → 3 scattering process. The fits to the observed GCE spectrum from this framework, across a range of viable model parameters, are comparable to those from DM annihilation and millisecond pulsar solutions in the literature.

Speaker: Debopam Goswami (Department of Physics & Astronomy, Texas A&M University)

14 TBD

15 Talkitos

15:30 Coffee Break

Friday Afternoon: Friday Afternoon 2

Convener: Andrew Long (Rice University)

16 Talkitos

17 TBD -- Cristian Vargas

18 Cosmic Trajectories Through the QCD Phase Diagram

We study the thermodynamic trajectory of the early Universe through the QCD phase diagram during the cosmological QCD transition, using a state-of-the-art lattice QCD equation of state with 2+1+1 quark flavors. Enforcing baryon-number conservation, electric-charge neutrality, and individual lepton-flavor asymmetry conservation, we explore both symmetric and flavor-asymmetric lepton configurations consistent with cosmological bounds. In the flavor-asymmetric case, we identify a robust mechanism — driven by the lepton-mass hierarchy and charge neutrality — that enforces a universal upper bound on the baryon chemical potential along any cosmological trajectory with small total lepton asymmetry. Comparing our results with current lattice QCD estimates of the QCD critical endpoint, all trajectories consistent with observational constraints lie safely in the crossover region, ruling out a first-order QCD phase transition in standard cosmological scenarios.

Speaker: Claudia Ratti

19 Probing Strong-Field Physics in X-ray Emission from Magnetized Neutron Stars

During the last five years, the Imaging X-ray Polarimetry Explorer (IXPE) has provided intensity and polarization information on the soft X-ray signals from the surfaces of seven magnetars. This multi-faceted dataset bolsters the ability to probe magnetar geometry and physics with new levels of insight. In support of these advances, we have developed and enhanced a sophisticated Monte Carlo simulation of radiative transport in highly-magnetized neutron star atmospheres. The code, named MAGTHOMSCATT, includes treatment of general relativistic light propagation and the influences of QED vacuum birefringence in the magnetosphere. Probes of geometry are presented for the radio magnetar 1E 1547-5408, indicating that both the magnetic axis and the viewer direction are close to being aligned with the rotation axis. In this talk, I will discuss how combined radio and IXPE X-ray polarization data for this magnetar provides strong evidence for the action of vacuum birefringence in its magnetosphere, advancing the case for a sought-after proof of this fundamental QED physics effect.

Speaker: Hoa Dinh (Rice University)

20 Talkitos

18:00 Dinner

Saturday 24 October

08:00 Coffee, juice, and breakfast

Saturday Morning

Convener: Kevin Huffenberger (Texas A&M University)

21 Maping the nanohertz gravitational sky

Pulsar timing arrays (PTAs) have announced evidence for the presence of a nanohertz gravitational wave background (GWB). However, we do not yet know the source of this GWB. In this talk, after a brief introduction to PTAs, I will describe how spatial mapping of the GWB can provide information beyond that available from just its spectrum. I will also introduce some new methods and insights in the search for anisotropy. I will end with a brief discussion on how anisotropy in combination with the spectrum of the GWB may allow us to disentangle one produced by supermassive black hole binaries from cosmological sources.

Speaker: Prof. Nihan Pol (Texas Tech University)

22 Seeing the Light: Supermassive Black Hole Binaries

Binary supermassive black holes are expected to be common based on models of hierarchical structure formation and observations of galaxy merger rates. Their electromagnetic counterparts, however, are extremely challenging to detect, due mainly to degeneracies with other phenomena. I will discuss the possible observational signatures and existing candidates for supermassive black hole pairs and extreme mass ratio inspirals. I will also describe their potential detectability using existing and planned missions and surveys up to the launch of the LISA mission.

Speaker: Prof. Krista Lynne Smith (Texas A&M University)

23 TBD -- Bai-Chiang Chiang

10:20 Coffee Break

Saturday Morning: Saturday Morning 2

Convener: Louis Strigari (Texas A&M)

24 TBD -- Masoom Singh

Speaker: Masoom Singh (Texas A&M University)

25 Spectropolarimetry of Supernovae

I will present results from spectropolarimetry of various supernovae obtained by the UC Berkeley group primarily at Lick Observatory. These include the Type Ia SN 2019ein, as well as the Type II SNe 2021jya and 2023ixf, among others. Various interesting results have been obtained and will be described.

Speaker: Prof. Alex Filippenko (UC Berkeley)

26 TBD -- Ben Rose

12:20 Lunch

Saturday Afternoon

Convener: James Dent (Sam Houston State University)

27 Measuring shapes of triaxial galaxy clusters using weak lensing observations

Galaxy clusters' 3D mass distributions are generally triaxial, a geometry that is difficult to constrain from projected observations. In this talk, I will explore the usefulness of measuring galaxy cluster shapes and briefly introduce the theoretical foundations for making these measurements. We measure ensemble halo ellipticity on the plane of the sky via axis-aligned stacking and multipole expansion of weak lensing signatures. To prepare for the next generation of optical datasets, such as those from the Rubin Observatory, I’ll showcase measured ellipticity in precursor datasets (Dark Energy Survey Year 3) and simulations, along with the systematics involved.

Speaker: Dr Radhakrishnan Srinivasan (Southern Methodist University)

28 Solar Constraints on Heavy Neutral Leptons with Tau Neutrino Mixing

Speaker: Vedran Brdar (Oklahoma State University (US))

29 TBD -- Nityasa Mishra

Speaker: Nityasa Mishra

30 TBD -- Anil Thapa

Speaker: Anil Thapa (Colorado State University)

31 Closing

Speaker: Kevin Huffenberger (TAMU)