Opening Remarks

• Marcela Carena (Perimeter Institute for Theoretical Physics)
• Kendrick Smith (Perimeter Institute for Theoretical Physics)

Room: PI/2-292 - Time Room

Cosmology: the last 25 years

• Matias Zaldarriaga (Institute for Advanced Study)

Room: PI/2-292 - Time Room I will reflect on the changes in the field during the last 25 years and reflect on where we are now. I will comment on what one might expect for the future.

Measuring H0 and dark energy with DESI

• Will Percival (University of Waterloo)

Room: PI/2-292 - Time Room The Dark Energy Spectroscopic Instrument (DESI) is the first of a new generation of Dark Energy experiments and probes evolution in the universe using galaxy clustering. Within the galaxy clustering signal, the projected location of the Baryon Acoustic Oscillations (BAO) acts as a standard ruler to map cosmic evolution. I will present the latest BAO results from the DESI Data Release 2 (DR2) sample, which contains 3 years of data, and their impact on our understanding of dark energy and neutrino masses. Finally, I will consider how the amplitude of the BAO signal can help us measure the Hubble constant, potentially helping to solve the Hubble tension.

Frontiers across central engines and their transients: mergers, explosions, jets, and nucleosynthesis

• Daniel Siegel (Universität Greifswald)

Room: PI/2-292 - Time Room

Right-Handed Neutrino Masses from the Electroweak Scale

• Brian Batell (University of Pittsburgh)

Room: PI/2-292 - Time Room Heavy right-handed neutrinos are highly motivated due to their connection with the origin of neutrino masses via the seesaw mechanism. If the right-handed neutrino Majorana mass is at or below the weak scale, direct experimental discovery of these states is possible in laboratory experiments. However, there is no a priori basis to expect right-handed neutrinos to be so light since the Majorana mass is a technically natural parameter and could comfortably reside at any scale, including at scales far above the weak scale. Here we explore the possibility that the right-handed neutrino Majorana mass originates from electroweak symmetry breaking. Working within an effective theory with two Higgs doublets, nonzero lepton number is assigned to the bilinear operator built from the two Higgs fields, which is then coupled to the right-handed neutrino mass operator. In tandem with the neutrino Yukawa coupling, following electroweak symmetry breaking a seesaw mechanism operates, generating the light SM neutrino masses along with right-handed neutrinos with masses below the electroweak scale. This scenario leads to novel phenomenology in the Higgs sector, which may be probed at the LHC and at future colliders. There are also interesting prospects for neutrinoless double beta decay and lepton flavor violation. We also explore some theoretical aspects of the scenario, including the technical naturalness of the effective field theory and ultraviolet completions of the right-handed neutrino Majorana mass.

Observable B modes from Cosmological Phase Transitions

• Gordon Krnjaic (Fermi National Accelerator Laboratory)

Room: PI/2-292 - Time Room

Neutron Star Mergers: Probes of Extreme Matter

• Pablo Bosch Gomez (Utrecht University)

Room: PI/2-292 - Time Room Binary neutron star mergers are critical for understanding the dynamics of dense matter, the origin of gravitational waves, and the formation channels of the heaviest elements through the r-process. I will review how long-lived remnants can act as central engines for multimessenger observations. I will then discuss how we can identify phase transitions within neutron stars or their remnants using such observations. Phase transitions alter the system’s dynamics and can produce distinct observable signatures, potentially detectable with next-generation facilities and observatories. These signatures can be used to probe matter at supranuclear densities and to test fundamental physics.

Can LIGO Detect Daylight Savings Time?

• Reed Essick (University of Toronto)

Room: PI/2-292 - Time Room An unavoidable part of studying astrophysics based on catalogs of detected events is quantifying the probability of detecting different types of events. I will briefly discuss the types of design considerations that go into constructing such estimates and how they will scale with larger catalog sizes. I will also introduce the wide variety of uses for such data products, including uncovering unexpected features within the data caused by the fact that humans build and operate the detectors.

Status and Prospects of AI Reasoning in Theoretical Physics

• Moritz Munchmeyer (University of Wisconsin–Madison)

Room: PI/2-292 - Time Room I will give a brief review of how large-language models are now being used for theoretical physics research. I will show the rapid progress of these models at the example of the TPBench benchmark, and present our recent work on improving their reliability with a symbolic verification agent and test-time scaling techniques. I will also discuss whether these models are truly reasoning and speculate how we might improve their performance in our field in the future.

Astrophysical Lessons from the Fourth Gravitational Wave Transient Catalog.

• Maya Fishbach (Canadian Institute for Theoretical Astrophysics (CITA))

Room: PI/2-292 - Time Room

Maximal Entanglement and Symmetries in Two Higgs Doublet Models

• Carlos Wagner (University of Chicago)

Room: PI/2-292 - Time Room

Quantum cosmology, gravitational waves and fast radio bursts: common insights from Picard-Lefshetz theory and Resurgence

• Ue-Li Pen (University of Toronto)

Room: PI/2-292 - Time Room

Pi in the Sky: Neutron Stars with Exceptionally Light QCD Axions

• Masha Baryakhtar (University of Washington)

Room: PI/2-292 - Time Room

Tests of Baryon Creation in the Early Universe

• David Morrissey (TRIUMF)

Room: PI/2-292 - Time Room Cosmological observations provide strong motivation for new physics beyond the Standard Model (SM). In addition to dark energy, and dark matter, the measured density of ordinary matter presents a further challenge to the SM. Creating enough baryons in the early universe to match what is seen today is difficult, and the SM does not appear to be able to do so. In this talk I will present some of the most promising mechanisms for baryogenesis and discuss how they will be tested by planned and proposed future experiments.

Light Dark Matter: showcases from cosmology to experiment

• Josef Pradler (Austrian Academy of Sciences & University of Vienna)

Room: PI/2-292 - Time Room In this talk, I will survey sub-GeV scale dark matter options with one showcase from cosmology and another showcase from direct detection On the cosmology side, I’ll demonstrate how SIMP dark sectors with bound states achieve the relic density through even-numbered annihilations only, and, at the same time, catalyze the usually considered 3->2 annihilations, enlarging the prospective parameter space. On the direct detection side, I’ll report progress toward a time-resolved Migdal framework that relaxes the impulse approximation used in most atomic-target analyses.

Phenomenological consequences of phase transitions occurred during inflation

• Haipeng An (Tsinghua University)

Room: PI/2-292 - Time Room In slow-roll inflationary models, the inflaton can undergo excursions on the order of the Planck scale, leading to significant changes in the properties of fields coupled to the inflaton, referred to as spectator fields. These changes may result in transitions between weakly and strongly interacting regimes, or even alterations in mass squared within the spectator field sector during inflation. Such dynamics can induce phase transitions, which have profound implications for the early Universe. In this talk, I will explore the phenomenological consequences of these phase transitions, focusing on the production of gravitational waves, curvature perturbations, non-Gaussianities, dark matter, and baryon number. I will also demonstrate how gravitational waves generated by scalar perturbations induced by phase transitions may potentially explain the alleged gravitational wave signals observed in recent pulsar timing array studies.

Extracting the universe’s expansion history from small-scale structure

• Adrienne Erickcek (UNC Chapel Hill)

Room: PI/2-292 - Time Room How did the universe evolve prior to the creation of the cosmic microwave background? There are no direct observational probes of the universe’s expansion history prior to the onset of Big Bang nucleosynthesis (BBN), and numerous theories predict deviations from radiation domination during the universe’s first second. Meanwhile, a persistent discrepancy between local and cosmological measurements of the Hubble constant has prompted us to reconsider the evolution of the universe between BBN and recombination. Since the growth of dark matter density perturbations depends on the expansion rate, deviations from the standard expansion history leave imprints on the matter power spectrum. I will discuss how adding decaying massive particles or fast-rolling scalar fields to the standard cosmological model impacts the abundance and structure of dark matter halos. Both cases illustrate how small-scale structure provides a powerful probe of the evolution of the universe prior to recombinatio

PN still alive : analytical waveforms to challenge GR

• Laura Bernard (Laboratoire Univers et Théories (LUTH))

Room: PI/2-292 - Time Room In this talk, I will give an overview of why the PN formalism is still relevant to model gravitational waves, focusing on recent synergies with other techniques and research topics. Taking the example of EFT-inspired higher curvature gravity theories, I will present a way towards building better gravitational wave tests to be used by next generation detectors.

Axion-Mediated Dark Matter: Models and Future Experimental Opportunities

• Stefania Gori (University of California, Santa Cruz)

Room: PI/2-292 - Time Room Dark matter (DM) remains one of the most enduring mysteries in fundamental physics, motivating a wide array of theoretical models and experimental searches. Axions and axion-like particles (ALPs) are theoretically well-motivated, as they naturally arise from theories with broken global symmetries. These particles may serve as viable DM candidates themselves or act as mediators between DM and the Standard Model. In this talk, I will present an overview of axion and axion-mediated DM models, including both classic QCD axions and broader classes of ALPs. Emphasis will be placed on novel mechanisms shaping the cosmic DM abundance, and on innovative strategies for detecting these elusive particles. I will highlight how forthcoming laboratory efforts, such as fixed-target and direct detection experiments, alongside astrophysical observations, are poised to explore uncharted regions of parameter space and deepen our understanding of the connections between axion physics and dark matter.

The future of high mass dark matter

• Joseph Bramante (Queen's University)

Room: PI/2-292 - Time Room A number of theories predict heavy dark matter, including WIMPs and high mass composite states formed in the early universe. Discovering the heaviest dark matter candidates, with a unit mass in excess of a microgram, requires methods beyond traditional underground experiments. For high mass dark matter searches in general (including WIMPS) new search methods will be necessary in the coming decades. I will discuss the most trenchant past searches for high mass dark matter along with future prospects.

The Big Bang as a Mirror

• Latham Boyle (University of Edinburgh)

Room: PI/2-292 - Time Room

Gravitational-wave astronomy: progress and prospects

• Patrick Brady (University of Wisconsin-Milwaukee)

Room: PI/2-292 - Time Room

Quantum Information Meets Particle Physics

• Ian Low (Argonne National Laboratory)

Room: PI/2-292 - Time Room

Big Bang Nucleosynthesis as a Probe of New Physics

• Tim Tait (University of California, Irvine)

Room: PI/2-292 - Time Room I will discuss BBN and a new python-based tool (PRyMordial) which allows one to easily simulate it both in the context of a standard cosmological model as well as in various scenarios of physics beyond the Standard Model. I’ll discuss how BBN provides a unique probe of physics relevant for the ~ MeV scale, and how it constrains or hints at modifications to the standard picture.

Ringing Black Holes

• Huan Yang (Tsinghua University)

Room: PI/2-292 - Time Room In this talk I will discuss one of the frontiers of both theory and data analysis in gravitational wave astronomy - understanding the ringing of black holes and probing them from real data. I will review past efforts started from Chandrasekhar, Detweiler, et al in analyzing modes of black holes and explain what we currently understand in both linear and nonlinear wave properties, as well as the corresponding detection aspect. At last I will show a few pressing problems and where we will be heading.

Dark matter searches with quantum computing systems

• Roni Harnik (Fermi National Accelerator Laboratory)

Room: PI/2-292 - Time Room

Light Fields and Scientific Fellowship: 16 years of interaction with Perimeter

• Renée Hložek (University of Toronto)

Room: PI/2-292 - Time Room The Perimeter Institute has provided me with 16 years of interactions, engagement and stimulating discussion. I'll describe some of my happy times at Perimeter and focus on one research area of interest: ultralight axions as a cosmological component. I'll describe constraints from the cosmic microwave background and large scale clustering of matter, through to novel constraints from voids and future prospects from stellar streams.

Ergoregion instability: the nonlinear story

• Nils Peter Siemonsen (Princeton University)

Room: PI/2-292 - Time Room Compact, spinning, and horizonless spacetimes can develop an ergoregion, where massless negative-energy states are quasi-trapped and drive the ergoregion instability. I will briefly review the linear mechanism and then describe recent progress in understanding the nonlinear evolution. Nonlinear mode coupling can amplify high-frequency modes through a turbulent direct cascade inside the ergoregion. Gravitational backreaction leads to an enhancement of the unstable process, and ultimately, black hole formation. I will illustrate the relevant dynamics and discuss implications for strongly gravitating horizonless systems.

Ultraswift: A coordinated effort to detect prompt EM emission from binary neutron star mergers

• Chad Hanna (Pennsylvania State University)

Room: PI/2-292 - Time Room To date only one astronomical event has been observed in both gravitational waves and electromagnetic waves -- the merger of two neutron stars known as GW170817. This event was detected in gamma rays simultaneously with gravitational waves, but was poorly localized initially. No other counterparts were detected until localization was improved leading to an 11 hour dearth of data in other EM wavelengths. GW170817 also demonstrated that realistic neutron star mergers may have off-axis GRB observations that could be sub-threshold in modern instruments. Here we describe an ongoing coordinated effort to detect binary neutron stars before they merge using gravitational waves and to slew NASA's Swift observatory to catch prompt potentially sub-threshold GRB and x-ray emission. If successful, this ambitious project would pin down the event location allowing for prompt follow-up observations across all other wavelengths. Multimessenger observations of binary neutron star mergers (gravitational waves and electromagnetic waves) have deep implications for nuclear physics, strong gravity and cosmology.

The Fast Transient Radio Sky

• Vicky Kaspi (Department of Physics, Trottier Space Institute)

Room: PI/2-292 - Time Room Fast Radio Bursts are a recently discovered phenomenon consisting of brief (typically few millisecond) bursts of radio waves coming from far outside our Milky Way galaxy, indeed from cosmological distances. Their origin is unknown. I will review what is known about these mysterious sources, and how they can act as novel probes of the matter distribution in the Universe. I will focus on results from the CHIME Fast Radio Burst Project, which uses a new Canadian digital radio telescope that is revolutionizing our view of the fast transient sky. I will also introduce the CHIME/FRB Outriggers, which will enable precise sky localizations for >1000 CHIME FRBs, hence permit host galaxy ID and redshift determinations.

Particle Physics at the Intersection of Fields

• Yoni Kahn (University of Toronto)

Room: PI/2-292 - Time Room Over the past 25 years, particle physics has grown and thrived by making connections with other fields of physics and the physical sciences in general. As we look forward to the next 25 years, the flexible toolbox of high-energy physics can be put to use on a number of problems outside the traditional application of collider physics, and we should keep an open mind and go where the data leads us. I will give several examples of fruitful interdisciplinary collaborations in particle physics from my own research career, including condensed matter physics, quantum chemistry, quantum sensing, and machine learning.

The Transport of Specific Entropies in the Cosmic SuperWeb: CnuB, CMB, CgwB, CnucB, CIB as CsB components

• Richard Bond (University of Toronto)

Room: PI/2-292 - Time Room

Cosmology with the kSZ effect

• Mathew Madhavarcheril (University of Pennsylvania)

Room: PI/2-292 - Time Room Reflecting on 10 years of collaboration with the Perimeter Institute, I will discuss one of many exciting cosmological probes opened up by high-resolution observations of the cosmic microwave background (CMB), the kinetic Sunyaev Zeldovich (kSZ) effect.  PI has and continues to serve as an incubator for novel approaches with this probe that will shed light on the initial conditions of the universe and the particle nature of dark matter.  Realizing the full potential of the kSZ effect requires new data.  I will report on new results from the Simons Observatory, a path-breaking CMB survey that recently saw first light.

Looking at the last 25 years of particle physics at PI + going nuclear with dark sectors

• Maxim Pospelov (University of Minnesota)

Room: PI/2-292 - Time Room

Closing Remarks Room: PI/2-292 - Time Room