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DOE OSTI2026

Predicting the dark matter-baryon abundance ratio

We discuss relaxation solutions to the dark matter-baryon coincidence problem in the context of QCD axion dark matter. In relaxation solutions, a moduli dynamically adjusts the mass of dark matter and baryons until their energy densities are 𝒪⁡(1) the same. Because the QCD axion is heavily connected to QCD, scanning the QCD axion mass inherently also scans the proton mass. In the context of relaxation solutions, this implies that the ratio of dark matter to baryon abundances (Ω DM /Ω B ) is a ratio of beta functions showing that these models can only accommodate discrete values of ΩDM/ΩB thereby “predicting” the ratio of the dark matter to baryon abundances. The original composite axion model has only a single integer degree of freedom 𝑁, the size of the gauge group, and we show that when 𝑁 =8 the observed value of Ω DM /Ω B =5.36 is reproduced to within its percent level error bars. Novel tests of this model include more precise measurements of Ω DM /Ω B , a better lattice determination of the dependence of the proton mass on the high energy QCD gauge coupling, as well as more traditional tests such as fifth force experiments.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

BICEP/ Keck XII: Constraints on axionlike polarization oscillations in the cosmic microwave background

Here, we present a search for axionlike polarization oscillations in the cosmic microwave background (CMB) with observations from the Keck Array . A local axion field induces an all-sky, temporally sinusoidal rotation of CMB polarization. A CMB polarimeter can thus function as a direct-detection experiment for axionlike dark matter. We develop techniques to extract an oscillation signal. Many elements of the method are generic to CMB polarimetry experiments and can be adapted for other datasets. As a first demonstration, we process data from the 2012 observing season to set upper limits on the axion-photon coupling constant in the mass range 10 – 21 – 10 – 18 eV , which corresponds to oscillation periods on the order of hours to months. We find no statistically significant deviations from the background model. For periods larger than 24 hr (mass m < 4.8 × 10 – 20 eV ), the median 95% confidence upper limit is equivalent to a rotation amplitude of 0.68°, which constrains the axion-photon coupling constant to g Φ γ < ( 1.1 × 10 – 11 GeV – 1 ) m / ( 10 – 21 eV ) , if axionlike particles constitute all of the dark matter. The constraints can be improved substantially with data already collected by the BICEP series of experiments. Current and future CMB polarimetry experiments are expected to achieve sufficient sensitivity to rule out unexplored regions of the axion parameter space.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

BICEP/ K e c k XIV: Improved constraints on axionlike polarization oscillations in the cosmic microwave background

We present an improved search for axionlike polarization oscillations in the cosmic microwave background (CMB) with observations from the Keck Array . An all-sky, temporally sinusoidal rotation of CMB polarization, equivalent to a time-variable cosmic birefringence, is an observable manifestation of a local axion field and potentially allows a CMB polarimeter to detect axionlike dark matter directly. We describe improvements to the method presented in previous work, and we demonstrate the updated method with an expanded dataset consisting of the 2012–2015 observing seasons. We set limits on the axion-photon coupling constant for mass m in the range 10 - 23 – 10 - 18 eV , which corresponds to oscillation periods on the order of hours to years. Our results are consistent with the background model. For periods between 1 and 30 d ( 1.6 × 10 - 21 ≤ m ≤ 4.8 × 10 - 20 eV ), the 95%-confidence upper limits on rotation amplitude are approximately constant with a median of 0.27°, which constrains the axion-photon coupling constant to g φ γ < ( 4.5 × 10 - 12 GeV - 1 ) m / ( 10 - 21 eV ) , if axionlike particles constitute all of the dark matter. More than half of the collected BICEP dataset has yet to be analyzed, and several current and future CMB polarimetry experiments can apply the methods presented here to achieve comparable or superior constraints. In the coming years, oscillation measurements can achieve the sensitivity to rule out unexplored regions of the axion parameter space.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

Is the magnitude of the Peccei–Quinn scale set by the landscape?

Rather general considerations of the string theory landscape imply a mild statistical draw towards large soft SUSY breaking terms tempered by the requirement of proper electroweak symmetry breaking where SUSY contributions to the weak scale are not too far from m weak ~ 100 GeV. Such a picture leads to the prediction that m h ~ 125 GeV while most sparticles are beyond current LHC reach. Here we explore the possibility that the magnitude of the Peccei-Quinn (PQ) scale f a is also set by string landscape considerations within the framework of a compelling SUSY axion model. First, we examine the case where the PQ symmetry arises as an accidental approximate global symmetry from a more fundamental gravity-safe Z$R\atop{24}$$ symmetry and where the SUSY mu parameter arises from a Kim-Nilles operator. The pull towards large soft terms then also pulls the PQ scale as large as possible. Unless this is tempered by rather severe (unknown) cosmological or anthropic bounds on the density of dark matter, then we would expect a far greater abundance of dark matter than is observed. This conclusion cannot be negated by adopting a tiny axion misalignment angle θ i because WIMPs are also overproduced at large f a . Hence, we conclude that setting the PQ scale via anthropics is highly unlikely. Instead, requiring soft SUSY breaking terms of order the gravity-mediation scale m 3/2 ~ 10 -100 TeV places the mixed axion-neutralino dark matter abundance into the intermediate scale sweet zone where f a ~ 10 11 -10 12 GeV. We compare our analysis to the more general case of a generic SUSY DFSZ axion model with uniform selection on theta_i but leading to the measured dark matter abundance: this approach leads to a preference for f a ~ 10 12 GeV.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

Final Report for the ADMX Phase 2a Project at the University of Washington

This is a final report of the ADMX (Axion Dark Matter eXperiment) Phase 2a program. This program is a project allowing for a sensitive axion dark-matter search at higher axion masses. The Phase 2a program also prepares the project for lower temperature anticipated in later operations. The Phase 2a program includes sensitive data-taking operations at two cavity modes, TM010 and TM020, allowing for faster data-taking operations and extending the search to higher and plausible dark-matter axion masses.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

Exploring new physics with O(keV) electron recoils in direct detection experiments

Motivated by the recent XENON 1T results, we explore various new physics models that can be discovered through searches for electron recoils in O(keV)-threshold direct-detection experiments. First, we consider the absorption of axion-like particles, dark photons, and scalars, either as dark matter relics or being produced directly in the Sun. In the latter case, we find that keV mass bosons produced in the Sun provide an adequate fit to the data but are excluded by stellar cooling constraints. We address this tension by introducing a novel Chameleon-like axion model, which can explain the excess while evading the stellar bounds. We find that absorption of bosonic dark matter provides a viable explanation for the excess only if the dark matter is a dark photon or an axion. In the latter case, photophobic axion couplings are necessary to avoid X-ray constraints. Second, we analyze models of dark matter-electron scattering to determine which models might explain the excess. Standard scattering of dark matter with electrons is generically in conflict with data from lower-threshold experiments. Momentum-dependent interactions with a heavy mediator can fit the data with dark matter mass heavier than a GeV but are generically in tension with collider constraints. Next, we consider dark matter consisting of two (or more) states that have a small mass splitting. The exothermic (down)scattering of the heavier state to the lighter state can fit the data for keV mass splittings. Finally, we consider a subcomponent of dark matter that is accelerated by scattering off cosmic rays, finding that dark matter interacting though an O(100 keV)-mass mediator can fit the data. The cross sections required in this scenario are, however, typically challenged by complementary probes of the light mediator. Throughout our study, we implement an unbinned Monte Carlo analysis and use an improved energy reconstruction of the XENON 1T events.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

DC conductivities with momentum dissipation in Horndeski theories

In this paper, we consider two four-dimensional Horndeski-type gravity theories with scalar fields that give rise to solutions with momentum dissipation in the dual boundary theories. Firstly, we study Einstein-Maxwell theory with a Horndeski axion term and two additional free axions which are responsible for momentum dissipation. We construct static electrically charged AdS planar black hole solutions in this theory and calculate analytically the holographic DC conductivity of the dual field theory. We then generalize the results to include magnetic charge in the black hole solution. Secondly, we analyze Einstein-Maxwell theory with two Horndeski axions which are used for momentum dissipation. We obtain AdS planar black hole solutions in the theory and we calculate the holographic DC conductivity of the dual field theory. The theory has a critical point α+γΛ = 0, beyond which the kinetic terms of the Horndeski axions become ghost-like. The conductivity as a function of temperature behaves qualitatively like that of a conductor below the critical point, becoming semiconductor-like at the critical point. Beyond the critical point, the ghost-like nature of the Horndeski fields is associated with the onset of unphysical singular or negative conductivities. Some further generalisations of the above theories are considered also.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

Saxion cosmology for thermalized gravitino dark matter

In all supersymmetric theories, gravitinos, with mass suppressed by the Planck scale, are an obvious candidate for dark matter; but if gravitinos ever reached thermal equilibrium, such dark matter is apparently either too abundant or too hot, and is excluded. However, in theories with an axion, a saxion condensate is generated during an early era of cosmological history and its late decay dilutes dark matter. We show that such dilution allows previously thermalized gravitinos to account for the observed dark matter over very wide ranges of gravitino mass, keV < m 3/2 < TeV, axion decay constant, 10 9 GeV < f a < 10 16 GeV, and saxion mass, 10 MeV < m s < 100 TeV. Constraints on this parameter space are studied from BBN, supersymmetry breaking, gravitino and axino production from freeze-in and saxion decay, and from axion production from both misalignment and parametric resonance mechanisms. Large allowed regions of (m 3/2 , f a , m s ) remain, but differ for DFSZ and KSVZ theories. Superpartner production at colliders may lead to events with displaced vertices and kinks, and may contain saxions decaying to (WW, ZZ, hh), gg, γγ or a pair of Standard Model fermions. In conclusion, freeze-in may lead to a sub-dominant warm component of gravitino dark matter, and saxion decay to axions may lead to dark radiation.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

The photophobic ALP

We investigate models and phenomenology of a photophobic axion-like particle (ALP), an axion whose coupling to photons is maximally suppressed without fine-tuning of the underlying parameters. We demonstrate that photophobia can be a natural UV property of ALP models and determine the irreducible coupling of photophobic ALPs to photons induced by violations of the axion shift symmetry. The signatures of photophobic axions are radically different from those of typical ALPs and are of particular interest for collider-based experiments, for which Standard Model triboson measurements provide a significant probe at higher masses. A variety of terrestrial and astrophysical measurements constrain the parameter space of photophobic ALPs, though bounds are typically much weaker compared to typical ALPs. We propose implications for particle production relaxion models based on photophobic ALPs, finding that they are in mild tension with existing experimental constraints.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Phases of inflation

Motivated by the 4d effective field theories for closed string axions in Type II string compactifications with D-branes, we consider chiral gauge theories coupled to multiple axions. We discuss how well-known non-perturbative dynamical phenomena, such as gauge instantons, fermion confinement and Nambu-Jona-Lasinio interactions, give rise to non-trivial vacuum configurations in the IR. The fluctuations about the IR vacuum are captured by some remaining closed string axions and infladrons (scalar chiral condensate excitations), which acquire dynamical masses. By employing the full power of the effective field theory, we investigate the applicability of these IR theories as inflationary models (natural, monodromy, Starobinsky) and connect different types of inflationary scenarios to different phases of the non-Abelian gauge theory or the Nambu-Jona-Lasinio four-fermion couplings. The back-reaction of the infladrons flattens the axion potential in natural-like inflationary models, such that the tension with current CMB data with respect to the spectral index and the tensor-to-scalar ratio can be partially alleviated.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2013

Low-energy effective field theory for chromo-natural inflation

Chromo-natural inflation is a novel model of inflation which relies on the existence of non-abelian gauge fields interacting with an axion. In its simplest realization, an SU(2) gauge field is assumed to begin inflation in a rotationally invariant VEV. The dynamics of the gauge fields significantly modifies the equations of motion for the axion, providing an additional damping term that supports slow-roll inflation, without the need to fine tune the axion decay constant. We demonstrate that in an appropriate slow-roll limit it is possible to integrate out the massive gauge field fluctuations whilst still maintaining the nontrivial modifications of the gauge field to the axion. In this slow-roll limit, chromo-natural inflation is exactly equivalent to a single scalar field effective theory with a non-minimal kinetic term, i.e. a P(X,χ) model. This occurs through a precise analogue of the gelaton mechanism, whereby heavy fields can have unsuppressed effects on the light field dynamics without contradicting decoupling. The additional damping effect of the gauge fields can be completely captured by the non-minimal kinetic term of the single scalar field effective theory. We utilize the single scalar field effective theory to infer the power spectrum and non-gaussianities in chromo-natural inflation and confirm that the mass squared of all the gauge field fluctuations is sufficiently large and positive that they completely decouple during inflation. These results confirm that chromo-natural inflation is a viable, stable and compelling model for the generation of inflationary perturbations.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Freeze-In dark matter with displaced signatures at colliders

Dark matter, X, may be generated by new physics at the TeV scale during an early matter-dominated (MD) era that ends at temperature T{sub R}≪ TeV. Compared to the conventional radiation-dominated (RD) results, yields from both Freeze-Out and Freeze-In processes are greatly suppressed by dilution from entropy production, making Freeze-Out less plausible while allowing successful Freeze-In with a much larger coupling strength. Freeze-In is typically dominated by the decay of a particle B of the thermal bath, B→X. For a large fraction of the relevant cosmological parameter space, the decay rate required to produce the observed dark matter abundance leads to displaced signals at LHC and future colliders, for any m{sub X} in the range keV <m{sub X}<m{sub B} and for values of m{sub B} accessible to these colliders. This result applies whether the early MD era arises after conventional inflation, when T{sub R} is the usual reheat temperature, or is a generic MD era with an alternative origin. In the former case, if m{sub X} is sufficiently large to be measured from kinematics, the reheat temperature T{sub R} can be extracted. Our result is independent of the particular particle physics implementation of B→X, and can occur via any operator of dimension less than 8 (4) for a post-inflation (general MD) cosmology. An interesting example is provided by DFS axion theories with TeV-scale supersymmetry and axino dark matter of mass GeV to TeV, which is typically overproduced in a conventional RD cosmology. If B is the higgsino, h-tilde, Higgs, W and Z particles appear at the displaced decays, h-tilde→ha-tilde, Za-tilde and h-tilde{sup ±}→W{sup ±}a-tilde. The scale of axion physics, f, is predicted to be in the range (3×10{sup 8}−10{sup 12}) GeV and, over much of this range, can be extracted from the decay length.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Expansion in higher harmonics of boson stars using a generalized Ruffini-Bonazzola approach. Part 1. Bound states

The method pioneered by Ruffini and Bonazzola (RB) to describe boson stars involves an expansion of the boson field which is linear in creation and annihilation operators. This expansion constitutes an exact solution to a non-interacting field theory, and has been used as a reasonable ansatz for an interacting one. In this work, we show how one can go beyond the RB ansatz towards an exact solution of the interacting operator Klein-Gordon equation, which can be solved iteratively to ever higher precision. Our Generalized Ruffini-Bonazzola approach takes into account contributions from nontrivial harmonic dependence of the wavefunction, using a sum of terms with energy $k\,E_0$, where $k\geq1$ and $E_0$ is the chemical potential of a single bound axion. The method critically depends on an expansion in a parameter $\Delta \equiv \sqrt{1-E_0{}^2/m^2}<1$, where $m$ is the mass of the boson. In the case of the axion potential, we calculate corrections which are relevant for axion stars in the transition or dense branches. We find with high precision the local minimum of the mass, $M_{min}\approx 463\,f^2/m$, at $\Delta\approx0.27$, where $f$ is the axion decay constant. This point marks the crossover from transition to dense branches of solutions, and a corresponding crossover from structural instability to stability.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

Constraints on dark photons and axionlike particles from the SuperCDMS Soudan experiment

We present an analysis of electron recoils in cryogenic germanium detectors operated during the SuperCDMS Soudan experiment. The data are used to set new constraints on the axioelectric coupling of axion-like particles and the kinetic mixing parameter of dark photons, assuming the respective species constitutes all of the galactic dark matter. This study covers the mass range from 40 eV/$c^2$ to 500 eV/$c^2$ for both candidates, excluding previously untested parameter space for masses below ~1 keV/$c^2$. For the kinetic mixing of dark photons, values below $10^{-15}$ are reached for particle masses around 100 eV/$c^2$; for the axioelectric coupling of axion-like particles, values below $10^{-12}$ are reached for particles with masses in the range of a few-hundred eV/$c^2$.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2020

Detecting axionlike dark matter with linearly polarized pulsar light

QCD axions or axionlike particles are among the most popular candidates for cold dark matter (DM) in the Universe. We proposed to detect axionlike DM, using linearly polarized pulsar light as a probe. Because of birefringence effect potentially caused by an oscillating galactic axion DM background, when pulsar light travels across the Galaxy, its linear polarization angle may vary with time. With a soliton + NFW galactic DM halo profile, we show that this strategy can potentially probe an axion-photon coupling as small as ~10 –13 GeV –1 for axion mass $m_a$ ~ 10 –22 –10 –20 eV , given the current measurement accuracy. An exclusion limit stronger than CAST (~ 10 –10 GeV –1 ) and SN1987A (~ 10 –11 GeV –1 ) could be extended up to $m_a$ ~ 10 –18 eV and ~10 –19 eV, respectively.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2025

NuSTAR Bounds on Radiatively Decaying Particles from M82

Axions and other putative feebly interacting particles with a mass of tens to several hundreds of keVs can be produced in stellar cores with a Lorentz boost factor E a / m a ≲ 10 . Thus, starburst galaxies such as M82 are efficient factories of slow axions. Their decay a → γ γ would produce a large flux of x-ray photons, peaking around 100 keV and spread around the Galaxy by an angle that can be relatively large. We use observations of the Nuclear Spectroscopic Telescope Array mission to show that the absence of these features can constrain 30–500 keV axion masses into uncharted regions for axion-photon coupling of g a γ ∼ 10 − 10 – 10 − 12 GeV − 1 . Our argument can be applied to other heavy feebly interacting particles and astrophysical sources that are hot enough to produce them, yet cold enough to avoid large boost factors which slow down the decay. Published by the American Physical Society 2025

Candón, Francisco R. (ORCID:0009000231999278)↗
DOE OSTI2019

Constraints on bosonic dark matter from ultralow-field nuclear magnetic resonance

The nature of dark matter, the invisible substance making up over 80% of the matter in the universe, is one of the most fundamental mysteries of modern physics. Ultralight bosons such as axions, axion-like particles, or dark photons could make up most of the dark matter. Couplings between such bosons and nuclear spins may enable their direct detection via nuclear magnetic resonance (NMR) spectroscopy: As nuclear spins move through the galactic dark-matter halo, they couple to dark matter and behave as if they were in an oscillating magnetic field, generating a dark-matter–driven NMR signal. As part of the cosmic axion spin precession experiment (CASPEr), an NMR-based dark-matter search, we use ultralow-field NMR to probe the axion-fermion “wind” coupling and dark-photon couplings to nuclear spins. No dark matter signal was detected above background, establishing new experimental bounds for dark matter bosons with masses ranging from 1.8 × 10 -16 to 7.8 × 10 -14 eV.

Science & Technology - Other Topics↗
DOE OSTI2022

Rapid Acceleration of Outcomes in Physics: Final Report for the Nuclear Physics, Particle Physics, Astrophysics, and Cosmology (NPAC) Umbrella Project

The Nuclear Physics, Particle Physics, Astrophysics, and Cosmology (NPAC) Initiative addresses the first question by supporting experiments that would directly detect dark matter when it interacts with very sensitive detectors. There are two leading candidates for dark matter that are plausibly detectable in terrestrial searches: axions and weakly-interacting massive particles, or WIMPs. Early NPAC investments supported PNNL involvement in the Axion Dark Matter eXperiment (ADMX), which has produced the world’s most sensitive axion search to date. Work associated with the current generation of the experiment is funded by the DOE Office of High Energy Physics (HEP), while R&D toward future searches for higher mass axions proceeds under NPAC. Likewise, early NPAC support for WIMP searches has graduated to the HEP-supported Super Cold Dark Matter Search (SuperCDMS) experiment. SuperCDMS has produced world-leading limits on potential WIMP candidates as well as a number of other exotic candidates and processes.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗