Axions and other very weakly interacting slim particles (WISPs) may be non-thermally produced in the early universe and survive as constituents of the dark universe. We describe their theoretical ...motivation and their phenomenology. A huge region in parameter space spanned by their couplings to photons and their masses can give rise to the observed cold dark matter abundance. A wide range of experiments – direct dark matter searches exploiting microwave cavities, searches for solar axions or WISPs, and light-shining-through-a-wall searches – can probe large parts of this parameter space in the foreseeable future.
We review searches for closed string axions and axion–like particles (ALPs) in IIB string flux compactifications. For natural values of the background fluxes and TeV scale gravitino mass, the moduli ...stabilisation mechanism of the LARGE Volume Scenario predicts the existence of a QCD axion candidate with intermediate scale decay constant, fa ~ 109÷12 GeV, associated with the small cycles wrapped by the branes hosting the visible sector, plus a nearly massless and nearly decoupled ALP associated with the LARGE cycle. In setups where the visible sector branes are wrapping more than the minimum number of two intersecting cycles, there are more ALPs which have approximately the same decay constant and coupling to the photon as the QCD axion candidate, but which are exponentially lighter. There are exciting phenomenological opportunities to search for these axions and ALPs in the near future. For fa ~ 1011÷12 GeV, the QCD axion can be the dominant part of dark matter and be detected in haloscopes exploiting microwave cavities. For fa ~ 109÷10 GeV, the additional ALPs could explain astrophysical anomalies and be searched for in the upcoming generation of helioscopes and light–shining–through–a–wall experiments.
A
bstract
We propose a model for the QCD axion which is realized through a coupling of the Peccei-Quinn scalar field to magnetically charged fermions at high energies. We show that the axion of this ...model solves the strong CP problem and then integrate out heavy magnetic monopoles using the Schwinger proper time method. We find that the model discussed yields axion couplings to the Standard Model which are drastically different from the ones calculated within the KSVZ/DFSZ-type models, so that large part of the corresponding parameter space can be probed by various projected experiments. Moreover, the axion we introduce is consistent with the astrophysical hints suggested both by anomalous TeV-transparency of the Universe and by excessive cooling of horizontal branch stars in globular clusters. We argue that the leading term for the cosmic axion abundance is not changed compared to the conventional pre-inflationary QCD axion case for axion decay constant
f
a
>
10
12
GeV.
The existence of a cosmic neutrino background – the analogue of the cosmic microwave background – is a fundamental prediction of standard big bang cosmology. Up to now, the observational evidence for ...its existence is rather indirect and rests entirely on cosmological observations of, e.g., the light elemental abundances, the anisotropies in the cosmic microwave background, and the large scale distribution of matter. Here, we review more direct, weak interaction based detection techniques for the cosmic neutrino background in the present epoch and in our local neighbourhood. We show that, with current technology, all proposals are still off by some orders of magnitude in sensitivity to lead to a guaranteed detection of the relic neutrinos. The most promising laboratory search, based on neutrino capture on beta decaying nuclei, may be done in future experiments designed to measure the neutrino mass through decay kinematics.
An even lighter QCD axion Di Luzio, Luca; Gavela, Belen; Quilez, Pablo ...
The journal of high energy physics,
05/2021, Letnik:
2021, Številka:
5
Journal Article
Recenzirano
Odprti dostop
A
bstract
We explore whether the axion which solves the strong CP problem can naturally be much lighter than the canonical QCD axion. The
Z
N
symmetry proposed by Hook, with
N
mirror and degenerate ...worlds coexisting in Nature and linked by the axion field, is considered in terms of generic effective axion couplings. We show that the total potential is safely approximated by a single cosine in the large
N
limit, and we determine the analytical formula for the exponentially suppressed axion mass. The resulting universal enhancement of all axion interactions relative to those of the canonical QCD axion has a strong impact on the prospects of axion-like particle experiments such as ALPS II, IAXO and many others: experiments searching for generic axion-like particles have in fact discovery potential to solve the strong CP problem. The finite density axion potential is also analyzed and we show that the
Z
N
asymmetric background of high-density stellar environments sets already significant model-independent constraints: 3 ≤
N
≲ 47 for an axion scale
f
a
≲ 2
.
4 × 10
15
GeV, with tantalizing discovery prospects for any value of
f
a
and down to
N
∼ 9 with future neutron star and gravitational wave data, down to the ultra-light mass region. In addition, two specific ultraviolet
Z
N
completions are developed: a composite axion one and a KSVZ-like model with improved Peccei-Quinn quality.
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