An official website of the United States government
A bstract We study axion strings of hyperlight axions coupled to photons. Hyperlight axions — axions lighter than Hubble at recombination — are a generic prediction of the string axiverse. These axions strings produce a distinct quantized polarization rotation of CMB photons which is $$ \mathcal{O} $$ O ( α em ). As the CMB light passes many strings, this polarization rotation converts E-modes to B-modes and adds up like a random walk. Using numerical simulations we show that the expected size of the final result is well within the reach of current and future CMB experiments through the measurement of correlations of CMB B-modes with E- and T-modes. The quantized polarization rotation angle is topological in nature and can be seen as a geometric phase. Its value depends only on the anomaly coefficient and is independent of other details such as the axion decay constant. Measurement of the anomaly coefficient by measuring this rotation will provide information about the UV theory, such as the quantization of electric charge and the value of the fundamental unit of charge. The presence of axion strings in the universe relies only on a phase transition in the early universe after inflation, after which the string network rapidly approaches an attractor scaling solution. If there are additional stable topological objects such as domain walls, axions as heavy as 10 − 15 eV would be accessible. The existence of these strings could also be probed by measuring the relative polarization rotation angle between different images in gravitationally lensed quasar systems.
more »
« less
This content will become publicly available on November 30, 2025
"Cosmological and Astrophysical Probes of Axions" in Proceedings of the 19th Recontres du Vietnam, 2023-Windows on the Universe
I summarize several cosmological and astrophysical probes of axions and axion-like particles. Topics covered include an introduction to the Strong \textsf{CP} problem and axions, axion emission from compact stars and supernovae, the impact of axion dark radiation on the cosmic microwave background (CMB) anisotropies, and the imprint of axion strings on the CMB.
more »
« less
- Award ID(s):
- 2114024
- PAR ID:
- 10562287
- Publisher / Repository:
- Recontres du Vietnam
- Date Published:
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Nonrelativistic axions can be efficiently produced in the polar caps of pulsars, resulting in the formation of a dense cloud of gravitationally bound axions. Here, we investigate the interplay between such an axion cloud and the electrodynamics in the pulsar magnetosphere, focusing specifically on the dynamics in the polar caps, where the impact of the axion cloud is expected to be most pronounced. For sufficiently light axions , we show that the axion cloud can occasionally screen the local electric field responsible for particle acceleration and pair production, inducing a periodic nulling of the pulsar’s intrinsic radio emission. At larger axion masses, the small-scale fluctuations in the axion field tend to suppress the backreaction of the axion on the electrodynamics; however, we point out that the incoherent oscillations of the axion in short-lived regions of vacuum near the neutron star surface can produce a narrow radio line, which provides a complementary source of radio emission to the plasma-resonant emission processes identified in previous work. While this Letter focuses on the leading order correction to pair production in the magnetosphere, we speculate that there can exist dramatic deviations in the electrodynamics of these systems when the axion backreaction becomes nonlinear. Published by the American Physical Society2024more » « less
-
Carosi, G.; Rybka, G. (Ed.)An overview of our experimental program to search for axion and axion-like-particle (ALP) dark matter using nuclear magnetic resonance (NMR) techniques is presented. An oscillating axion field can exert a time-varying torque on nuclear spins either directly or via generation of an oscillating nuclear electric dipole moment (EDM). Magnetic resonance techniques can be used to detect such an effect. The first-generation experiments explore many decades of ALP parameter space beyond the current astrophysical and laboratory bounds. It is anticipated that future versions of the experiments will be sensitive to the axions associated with quantum chromodynamics (QCD) having masses <10^(−9) eV/c^2.more » « less
-
We study the impact of stellar cooling due to light axion emission on the formation and evolution of black hole binaries, via stable mass transfer and the common envelope scenario.~We find that in the presence of light axion emission, no binary black hole mergers are formed with black holes in the lower mass gap ($$M_{\rm BH} < 4 {\rm M}_\odot $$) via the common envelope formation channel.~In some systems, this happens because axions prevent Roche lobe overflow.~In others, they prevent the common envelope from being ejected.~Our results apply to axions with couplings $$ g_{a \gamma} \gtrsim 10^{-10}\, \rm GeV^{-1}$$ (to photons) or $$\alpha_{ae} \gtrsim 10^{-26} $$ (to electrons) and masses $$ m_a \ll 10 \, \rm keV$$.~Light, weakly coupled particles may therefore apparently produce a mass gap $$2 {\rm M}_\odot < M_{\rm BH} < 4 {\rm M}_\odot$$ in the LIGO/Virgo/KAGRA data, when no mass gap is present in the stellar remnant population.more » « less
-
Axionlike dark matter whose symmetry breaking occurs after the end of inflation predicts enhanced primordial density fluctuations at small scales. This leads to dense axion minihalos (or miniclusters) forming early in the history of the Universe. Condensation of axions in the minihalos leads to the formation and subsequent growth of axion stars at the cores of these halos. If, like the QCD axion, the axionlike particle has attractive self-interactions there is a maximal mass for these stars, above which the star rapidly shrinks and converts an O(1) fraction of its mass into unbound relativistic axions. This process would leave a similar (although in principle distinct) signature in cosmological observables as a decaying dark matter fraction, and thus is strongly constrained. We place new limits on the properties of axionlike particles that are independent of their nongravitational couplings to the standard model.more » « less
