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1. Axion minima in string theory

   https://doi.org/10.1007/JHEP02(2025)134  

   Gendler, Naomi; Janssen, Oliver; Kleban, Matthew; La_Madrid, Joan; Mehta, Viraf M (February 2025, Journal of High Energy Physics)

   A<sc>bstract</sc> We study the landscape of axion theories in compactifications of type IIB string theory on orientifolds of Calabi-Yau threefolds. In a sample of approximately 400,000 geometries we find that in the regime of perturbative control there are only a handful of distinct axion minima per geometry, despite there being infinitely many instanton contributions to the potential with unbounded charges. The ensemble we consider has numbers of axion fields ranging from 1 to 491, but the median number of distinct minima is 1, the mean number is 1.9 and the largest is 54. These small numbers of minima occur because the leading axion charge matrix is quite sparse, while the subleading corrections are increasingly exponentially suppressed as the charges increase. On their own, such potentials are nowhere near rich enough to be of interest anthropically. This is in stark contrast to potentials for which the charge matrix is less sparse or the hierarchies between the instanton contributions are less steep, where one can find$$ \mathcal{O}\left({10}^{500}\right) $$ $O\left({10}^{500}\right)$minima for$$ \mathcal{O}(500) $$ $O\left(500\right)$axions. To generate a sufficiently large landscape from string compactifications our results indicate that one would need to rely on varying flux or topology, or to develop tools that allow one to go beyond the regime we can control with current techniques. 

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2. Axion detection via superfluid 3He ferromagnetic phase and quantum measurement techniques

   https://doi.org/10.1007/JHEP09(2024)191  

   Chigusa, So; Kondo, Dan; Murayama, Hitoshi; Okabe, Risshin; Sudo, Hiroyuki (September 2024, Journal of High Energy Physics)

   A<sc>bstract</sc> We propose to use the nuclear spin excitation in the ferromagnetic A₁phase of the superfluid³He for the axion dark matter detection. This approach is striking in that it is sensitive to the axion-nucleon coupling, one of the most important features of the QCD axion introduced to solve the strong CP problem. We review a quantum mechanical description of the nuclear spin excitation and apply it to the estimation of the axion-induced spin excitation rate. We also describe a possible detection method of the spin excitation in detail and show that the combination of the squeezing of the final state with the Josephson parametric amplifier and the homodyne measurement can enhance the sensitivity. It turns out that this approach gives good sensitivity to the axion dark matter with the mass of$$ \mathcal{O} $$ $O$(1) μeV depending on the size of the external magnetic field. We estimate the parameters of experimental setups, e.g., the detector volume and the amplitude of squeezing, required to reach the QCD axion parameter space. 

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3. Investigating strangeness enhancement with multiplicity in pp collisions using angular correlations

   https://doi.org/10.1007/JHEP09(2024)204  

   Acharya, S; Adamová, D; Agarwal, A; Aglieri_Rinella, G; Aglietta, L; Agnello, M; Agrawal, N; Ahammed, Z; Ahmad, S; Ahn, S U; et al (September 2024, Journal of High Energy Physics)

   A<sc>bstract</sc> A study of strange hadron production associated with hard scattering processes and with the underlying event is conducted to investigate the origin of the enhanced production of strange hadrons in small collision systems characterised by large charged-particle multiplicities. For this purpose, the production of the single-strange meson$$ {\textrm{K}}_{\textrm{S}}^0 $$ $K_S^0$and the double-strange baryon Ξ^±is measured, in each event, in the azimuthal direction of the highest-p_Tparticle (“trigger” particle), related to hard scattering processes, and in the direction transverse to it in azimuth, associated with the underlying event, in pp collisions at$$ \sqrt{s} $$ $\sqrt{s}$= 5.02 TeV and$$ \sqrt{s} $$ $\sqrt{s}$= 13 TeV using the ALICE detector at the LHC. The per-trigger yields of$$ {\textrm{K}}_{\textrm{S}}^0 $$ $K_S^0$and Ξ^±are dominated by the transverse-to-leading production (i.e., in the direction transverse to the trigger particle), whose contribution relative to the toward-leading production is observed to increase with the event charged-particle multiplicity. The transverse-to-leading and the toward-leading Ξ^±/$$ {\textrm{K}}_{\textrm{S}}^0 $$ $K_S^0$yield ratios increase with the multiplicity of charged particles, suggesting that strangeness enhancement with multiplicity is associated with both hard scattering processes and the underlying event. The relative production of Ξ^±with respect to$$ {\textrm{K}}_{\textrm{S}}^0 $$ $K_S^0$is higher in transverse-to-leading processes over the whole multiplicity interval covered by the measurement. The$$ {\textrm{K}}_{\textrm{S}}^0 $$ $K_S^0$and Ξ^±per-trigger yields and yield ratios are compared with predictions of three different phenomenological models, namely Pythia8.2 with the Monash tune, Pythia8.2 with ropes and EPOS LHC. The comparison shows that none of them can quantitatively describe either the transverse-to-leading or the toward-leading yields of$$ {\textrm{K}}_{\textrm{S}}^0 $$ $K_S^0$and Ξ^±. 

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4. Indirect detection of hot dark matter

   https://doi.org/10.1007/JHEP05(2025)127  

   Dror, Jeff A; Sandick, Pearl; Haghi, Barmak_Shams Es; Yang, Fengwei (May 2025, Journal of High Energy Physics)

   A<sc>bstract</sc> Cosmologically stable, light particles that came into thermal contact with the Standard Model in the early universe may persist today as a form of hot dark matter. For relics with masses in the eV range, their role in structure formation depends critically on their mass. We trace the evolution of such hot relics and derive their density profiles around cold dark matter halos, introducing a framework for theirindirect detection. Applying this framework to axions — a natural candidate for a particle that can reach thermal equilibrium with the Standard Model in the early universe and capable of decaying into two photons — we establish stringent limits on the axion-photon couplingg_aγusing current observations of dwarf galaxies, the Milky Way halo, and galaxy clusters. Our results set new bounds on hot axions in the$$ \mathcal{O}\left(1-10\right) $$ $O\left(1-10\right)$eV range. 

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5. JAXVacua — a framework for sampling string vacua

   https://doi.org/10.1007/JHEP12(2023)146  

   Dubey, A; Krippendorf, S; Schachner, A (December 2023, Journal of High Energy Physics)

   A<sc>bstract</sc> Moduli stabilisation in string compactifications with many light scalars remains a major blind-spot in the string landscape. In these regimes, analytic methods cease to work for generic choices of UV parameters which is why numerical techniques have to be exploited. In this paper, we implement algorithms based on JAX, heavily utilising automatic differentiation, just-in-time compilation and parallelisation features, to efficiently construct string vacua. This implementation provides a golden opportunity to efficiently analyse large unexplored regions of the string landscape. As a first example, we apply our techniques to the search of Type IIB flux vacua in Calabi-Yau orientifold compactifications. We argue that our methods only scale mildly with the Hodge numbers making exhaustive studies of low energy effective field theories with$$ \mathcal{O} $$ $O$(100) scalar fields feasible. Using small computing resources, we are able to construct$$ \mathcal{O} $$ $O$(10⁶) flux vacua per geometry withh^1,2≥ 2, vastly out-performing previous systematic searches. In particular, we showcase the efficiency of our methods by presenting generic vacua with fluxes below the tadpole constraint set by the orientifold with up toh^1,2= 25 complex structure moduli. 

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