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Timothy Launders (Boston University)11/05/2026, 14:15Particle Cosmology
The exact abundances of light elements produced during Big Bang Nucleosynthesis (BBN) are highly sensitive to the physics of the primordial plasma. Percent-level measurements of primordial deuterium have enabled precision cosmology from BBN; to match this level of precision in theoretical calculations, a careful estimate of uncertainties arising from nuclear reaction cross sections is of...
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Dr Subhajit Ghosh (The University of Texas at Austin)11/05/2026, 14:30Particle Cosmology
In this talk, I will discuss a novel way of modeling neutrino self-interactions for cosmological observables. In this model, active neutrinos resonantly convert to self-interacting dark radiation after BBN but before the CMB epoch. It yields cosmological signatures equivalent to those of self-interacting neutrinos and naturally accommodates relaxed neutrino mass constraints. Our analysis shows...
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Marios Galanis (Stanford University)11/05/2026, 14:45
In this talk I will do three things. First, I will outline the conditions under which the interaction rate of inelastic processes with a system consisting of N targets scales as N^2. Second, I will present computations of interaction rates for several weakly interacting particles, including the cosmic neutrino background and axion dark matter, and will explain the underlying physics. Third, I...
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Dylan McCauley (Carnegie Mellon University)11/05/2026, 15:00Particle Cosmology
This study explores a "win-win" coupling between a scalar field and the cosmic neutrino background to address the Hubble tension and the cosmic coincidence problem. We propose a model featuring a scalar bosonic field with a scale-free, quartic scalar potential $U(\phi) = \lambda \phi^4$ that interacts with neutrinos to generate an effective potential with temperature-dependent degenerate...
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Antoni Bertolez-Martinez (University of Wisconsin-Madison)11/05/2026, 15:15Particle Cosmology
The high densities in the early Universe provide a unique laboratory to constrain couplings between feebly interacting particles, such as dark matter and neutrinos. I will introduce a model where neutrinos get their mass from a small diagonal coupling to ultralight dark matter (ULDM), and how to consistently use cosmology, namely Big Bang Nucleosynthesis (BBN), to constrain it. In particular,...
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Brian Zhang11/05/2026, 15:30Particle Cosmology
Primordial black holes can act as non-thermal sources of dark matter through Hawking evaporation, but the viable parameter space depends sensitively on greybody factors, massive-particle thresholds, and the full particle content of the dark sector. In this talk, I will examine the efficiency of the process by which a black hole dumps its mass into the creation of a population of dark matter...
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Duncan Rocha (University of Chicago)11/05/2026, 15:45Particle Cosmology
I will describe a novel cosmological scenario in which baryonic neutron stars could plausibly form in the early universe. If baryogenesis initially produces an excessively-large baryon asymmetry, the baryonic mass inside the horizon can exceed the minimum neutron star mass before big bang nucleosynthesis (BBN). While this large asymmetry is present, non-relativistic baryons can dominate the...
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Gil Paz11/05/2026, 16:30
Precision spectroscopic measurements of isotope shifts have recently reached a high level of accuracy. Tests of King non-linearity (NL) along isotope chains have been proposed as a tool to search for fifth-force mediators. At the same time, these tests can potentially teach us about the structure of heavy nuclei at unprecedented precision, where
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King NL has already been observed in several... -
Shourya Mukherjee11/05/2026, 16:45
We consider fifth forces mediated by an ultralight scalar that arises as a composite pseudo-Nambu-Goldstone boson from a strongly coupled hidden sector. In our framework, the scalar couples to the Standard Model through the hypercharge portal, and its interactions are softened above the compositeness scale by form factors. This can significantly weaken conventional equivalence principle (EP)...
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Swapnil Dutta11/05/2026, 17:00Particle Cosmology
In this talk, we look at some cosmological constraints on majoron dark matter in the singlet Majoron model. We consider two scenarios: pre-inflationary and post inflationary spontaneous lepton number symmetry breaking, while simultaneously demanding leptogenesis to happen, and neutrino masses being generated by the type I seesaw mechanism. We derive the constraints and future prospects to...
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Daven Wei Ren Ho11/05/2026, 17:15Particle Cosmology
Cosmological first-order phase transitions (FOPT) can occur in a secluded dark sector at relatively late times before recombination. Since bubble nucleation occurs stochastically as the FOPT unfolds, different regions of the universe transition at different times. On large scales, this random fluctuation sources a scalar curvature perturbation with a dimensionless power spectrum that scales...
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Isaac Wang11/05/2026, 17:30Particle Cosmology
A precise determination of the bubble wall velocity $v_w$ is crucial for making accurate predictions of the baryon asymmetry and gravitational wave (GW) signals in models of electroweak baryogenesis (EWBG).
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Working in the local thermal equilibrium approximation, we exploit entropy conservation to present efficient algorithms for computing $v_w$, significantly streamlining the calculation.
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Alize Sucsuzer (Tufts University)11/05/2026, 17:45Particle Cosmology
New long range forces acting on ordinary matter are highly constrained. However it is possible such forces act on dark matter, as it is less constrained observationally. In this work, we consider dark matter to be made of light bosons, such as axions. We introduce a mediator that communicates a new force between dark matter particles, in addition to gravity. The mediator is taken to be light,...
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Nathan Herring (Hillsdale College)11/05/2026, 18:00Particle Cosmology
We study the dynamics of a spatially homogeneous scalar (or pseudoscalar) condensate Yukawa-coupled to N_f fermionic degrees of freedom, with emphasis on the real-time processes governing misalignment, particle production, and entropy generation. Going beyond the effective potential framework, we develop a dynamical treatment in which the scalar condensate and fermionic sector are evolved...
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Manuel Diaz11/05/2026, 18:15Particle Cosmology
Cosmological models of emergent modified gravity allow departures from the dynamics of general relativity in the high and low-curvature regimes without additional degrees of freedom. Consequently, emergent modified gravity is not only able to replace the big bounce singularity with a nonsingular bounce from a purely modified gravity perspective without exotic matter fields, but also to...
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Antonios Kyriazis (University of Florida)12/05/2026, 14:00Particle Cosmology
Spontaneous symmetry breaking of global symmetries in the early universe may leave behind topological defects known as cosmic strings. These strings continuously emit the symmetryโs pseudo Nambu-Goldstone boson, which contributes to the dark matter density after it becomes non-relativistic. In the talk, I will discuss the numerical and analytical methods we developed to evaluate the density...
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Yunjia Bao (University of Chicago)12/05/2026, 14:15Particle Cosmology
We propose a general framework in which a phase transition is triggered during cosmic inflation by the slow-roll dynamics of a spectator field. The topological defects formed at the transition are inflated outside the horizon, reenter it after inflation, and can subsequently generate characteristic gravitational-wave (GW) signals. Quantum fluctuations of the spectator field modulate the timing...
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Dhong Yeon Cheong (University of Chicago)12/05/2026, 14:30Particle Cosmology
In this talk, I will formulate a new class of primordial perturbations called kinetic isocurvature perturbations, where the mass density of dark matter is constant relative to the photon number density while the kinetic energy of dark matter fluctuates in space. Such perturbations naturally arise in scenarios where a nonrelativistic heavy field decays into relativistic dark matter particles...
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Dr Itamar Allali (Brown University)12/05/2026, 14:45Particle Cosmology
The dynamics of the early universe has the possibility to imprint interesting features on the spectrum of primordial perturbations which serve as initial conditions for the standard hot big bang evolution and formation of structure at later times. In the inflationary paradigm, sharp features in the trajectory of the inflaton could lead to interesting deviations away from the standard...
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Zachary Cheslog (Stony Brook University)12/05/2026, 15:00Particle Cosmology
Many models of inflation and the early universe provide specific predictions for the values of the scalar spectral index $n_s$ and its running, $\alpha_s$. Considering current data from ACT DR6, Planck, SPT-3G DR1, and DESI DR2 it was found that key models of inflation, including the Starobinsky model, were ruled out at $2\sigma$. However we find that when additionally varying the number of...
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Zekai Wang (Harvard univeristy)12/05/2026, 15:15
The QCD axion in the pre-inflation scenario faces a stringent isocurvature constraint, which requires a relatively low Hubble scale during inflation. If the axion was heavier than the Hubble scale during inflation, its isocurvature is suppressed and the constraint disappears. We point out a novel mechanism for achieving this, relying on the topological nature of a BF-type (monodromy) mass for...
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Fengwei Yang (University of Notre Dame)12/05/2026, 15:30Particle Cosmology
We study cosmological perturbations sourced by a domain wall (DW) network with a finite lifetime. Allowing DWs to decay avoids the stringent CMB energy density constraints, enabling signals that are relevant for both the CMB and measurements sensitive to smaller scales (higher $k$-modes). Using the uncorrelated segment model (USM) to describe the DW energy-momentum tensor, we derive analytical...
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Alexander Cassem (Tufts University)12/05/2026, 15:45Particle Cosmology
Compact extra dimensions appear in various scenarios beyond the Standard Model (SM) of physics, including string theory, but their experimental signatures have not been observed yet. If the energy scale associated with extra dimensions is too high, then the signatures will not be observable in terrestrial colliders. The cosmological period of inflation, however, is an epoch where the energies...
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Dr Sai Chaitanya Tadepalli (Dept of Physics, Indiana University, Bloomington)12/05/2026, 16:30Particle Cosmology
CMB limits on isocurvature are often taken to exclude high-scale inflation with large QCD axion decay constants in pre-inflationary PQ models. We show this can be avoided via PQ field-space geometry.
With a nonlinear sigma-model kinetic term, the effective decay constant is enhanced during inflation, suppressing isocurvature without extra couplings or PQ breaking. For a hyperbolic...
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Matthew Baldwin12/05/2026, 16:45Particle Cosmology
Axions produced from dark matter decays can convert to photons in the magnetic fields of cosmological filaments, resulting in an isotropic gamma ray background flux. We present new indirect detection constraints on the axion mass and axion-photon coupling, for GeV- to TeV-scale dark matter with a decay lifetime below $10^{30}$ sec, by constraining this flux. We exclude significant parameter...
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Kunfeng Lyu12/05/2026, 17:00Particle Cosmology
The QCD axion is a well-motivated hypothetical particle beyond the Standard Model (SM) and a compelling dark matter candidate. Its relic abundance is highly sensitive to the thermal history of the universe when the temperature is around the QCD confinement scale. Meanwhile, the NANOGrav Collaboration has reported evidence for a stochastic gravitational wave background, which could originate...
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Badal Bhalla (University of Oklahoma)12/05/2026, 17:15
The temperature of baryons at the end of the cosmic dark ages can be inferred from observations of the 21-cm hyperfine transition in neutral hydrogen. Any energy injection from the dark sector can therefore be detected through these measurements. Dark compact objects and dark-matter substructures can modify the baryon temperature by transferring heat via dynamical friction. In this work, we...
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Rajrupa Mondal (University of Maryland College Park)12/05/2026, 17:30Particle Cosmology
A compelling production mechanism for QCD axion dark matter is from the scaling dynamics of early universe axion strings. We show that in DFSZ-like models containing tree-level interactions between fermions and the axion, friction between the thermal bath and the axion string drastically changes the behavior of the axion string network for lower $f_a$ values. Friction delays the onset of...
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Praniti Singh (Brown University (US))12/05/2026, 17:45Particle Cosmology
Measurements of the Cosmic Microwave Background (CMB) have confirmed a nearly scale-invariant primordial spectrum of adiabatic perturbations, in which the density fluctuations of radiation, baryons, and dark matter are in phase. However, primordial perturbations may also include an isocurvature component, in which the relative density fluctuations of individual species such as dark matter (DM)...
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Hengameh Bagherian (University of Chicago)12/05/2026, 18:00Particle Cosmology
We propose a minimal and natural dark-sector framework in which dark matter is composed of magnetic monopoles coupled to a light axion field. Through the Witten effect, the axion background induces electric charge on the monopoles, turning them into dyons that in turn modify the axion potential. This monopole-dependent axion mass provides a simple, radiatively stable mechanism for dark-sector...
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Chandrika Chandrashekar (Harvard University)12/05/2026, 18:15Particle Cosmology
Extra-dimensional scenarios for the QCD axion are well motivated to address the quality problem. However, like other pre-inflationary axion theories, they suffer from the axion isocurvature problem where QCD axion dark matter is incompatible with high scale inflation due to CMB isocurvature bounds. We tackle this problem by utilizing an additional ingredient generically predicted by extra...
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