More axions from strings

Models of Dark Matter (DM) can leave unique imprints on the Universe’s small scale structure by boosting density perturbations on small scales. We study the capability of Pulsar Timing Arrays to search for, and constrain, subhalos from such models. The models of DM we consider are ordinary adiabatic perturbations in ΛCDM, QCD axion miniclusters, models with early matter domination, and vector DM produced during inflation. We show that ΛCDM, largely due to tidal stripping effects in the Milky Way, is out of reach for PTAs. Axion miniclusters may be within reach, although this depends crucially on whether the axion relic density is dominated by the misalignment or string contribution. Models where there is matter domination with a reheat temperature below 1 GeV may be observed with future PTAs. Lastly, vector DM produced during inflation can be detected if it is lighter than 10−16 GeV. We also make publicly available a Python Monte Carlo tool for generating the PTA time delay signal from any model of DM substructure.

Section: Axions With Pq Symmetry Breaking After Inflationmentioning

confidence: 96%

Section: Axions With Pq Symmetry Breaking After Inflationmentioning

confidence: 99%

Probing small-scale power spectra with pulsar timing arrays

Lee

Mitridate

Trickle

et al. 2021

“…If the PQ symmetry is restored after inflation, model-dependent contribution of axion strings and domain-wall (DW) decays to axion DM must be taken into account, and are potentially dominant. According to the most recent numerical studies [60,61], computation uncertainties still allow for a relatively large axion mass window, the upper part of which (m a ∼ meV) would be at reach of IAXO. Moreover, models with long-lived DWs [62] would further increase the yield and point to QCD axions of 1 to 100 meV as those accounting for the totality of the Universe's DM.…”

Section: Jhep05(2021)137mentioning

confidence: 99%

Conceptual design of BabyIAXO, the intermediate stage towards the International Axion Observatory

Abeln¹,

Altenmüller²,

Cuendis³

et al. 2021

This article describes BabyIAXO, an intermediate experimental stage of the International Axion Observatory (IAXO), proposed to be sited at DESY. IAXO is a large-scale axion helioscope that will look for axions and axion-like particles (ALPs), produced in the Sun, with unprecedented sensitivity. BabyIAXO is conceived to test all IAXO subsystems (magnet, optics and detectors) at a relevant scale for the final system and thus serve as prototype for IAXO, but at the same time as a fully-fledged helioscope with relevant physics reach itself, and with potential for discovery. The BabyIAXO magnet will feature two 10 m long, 70 cm diameter bores, and will host two detection lines (optics and detector) of dimensions similar to the final ones foreseen for IAXO. BabyIAXO will detect or reject solar axions or ALPs with axion-photon couplings down to gaγ ∼ 1.5 × 10−11 GeV−1, and masses up to ma ∼ 0.25 eV. BabyIAXO will offer additional opportunities for axion research in view of IAXO, like the development of precision x-ray detectors to identify particular spectral features in the solar axion spectrum, and the implementation of radiofrequency-cavity-based axion dark matter setups.

“…The scaling regime persists over many orders of magnitude in temperature until T T QCD . The scaling of strings in the early universe has been extensively studied by numerical simulations [19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36]. The scaling behavior is the result of a balance between string length entering the horizon, and string length which is lost by the emission of unstable string loops due to efficient string reconnection.…”

Section: Jhep06(2021)052mentioning

confidence: 99%

Axion strings are superconducting

Fukuda

Manohar

Murayama

et al. 2021

We explore the cosmological consequences of the superconductivity of QCD axion strings. Axion strings can support a sizeable chiral electric current and charge density, which alters their early universe dynamics. We examine the possibility that shrinking axion string loops can become effectively stable remnants called vortons, supported by the repulsive electromagnetic force of the string current. We find that vortons in our scenario are generically unstable, and so do not pose a cosmological difficulty. Furthermore, if a primordial magnetic field (PMF) exists in the early universe, a large current is induced on axion strings, creating a significant drag force from interactions with the surrounding plasma. As a result, the strings are slowed down, which leads to an orders of magnitude enhancement in the number of strings per Hubble volume. Finally, we study potential implications for the QCD axion relic abundance. The QCD axion window is shifted by orders of magnitude in some parts of our parameter space.