The recently claimed anomaly in the measurement of the 21 cm hydrogen absorption signal by EDGES at <math><mi>z</mi><mo>∼</mo><mn>17</mn></math>, if cosmological, requires the existence of new physics. The possible attempts to resolve the anomaly rely on either (i) cooling the hydrogen gas via new dark matter-hydrogen interactions or (ii) modifying the soft photon background beyond the standard CMB one, as possibly suggested also by the ARCADE 2 excess. We argue that solutions belonging to the first class are generally in tension with cosmological dark matter probes once simple dark sector models are considered. Therefore, we propose soft photon emission by light dark matter as a natural solution to the 21 cm anomaly, studying a few realizations of this scenario. We find that the signal singles out a photophilic dark matter candidate characterised by an enhanced collective decay mechanism, such as axion mini-clusters.

Estonia

Sean Fraser

Andi Hektor

Gert Hütsi

Kristjan Kannike

Carlo Marzo

Luca Marzola

Antonio Racioppi

CERN

Martti Raidal

Christian Spethmann

Ville Vaskonen

Hardi Veermäe

The EDGES 21 cm anomaly and properties of dark matter

Recent measurements of semileptonic B-meson decays seemingly imply violations of lepton flavor universality beyond the Standard Model predictions. With three-level explanations based on extended Higgs sectors being strongly challenged by the measurements of the <math><msubsup><mi>B</mi><mi>c</mi><mo>−</mo></msubsup></math> lifetime, new theories invoking leptoquark or vector fields appear as the only feasible answer. However, in this work we show that simple scalar extensions of the Standard Model still offer a possible solution to the <math><mi>B</mi></math> physics puzzle, owing to sizeable loop-level corrections which mimic the effects of new vector contributions. Considering a simplified model characterized by a charged and a neutral scalar particle, we verify the compatibility of the observed <math><msub><mi>R</mi><msup><mi>D</mi><mrow><mo>(</mo><mo>*</mo><mo>)</mo></mrow></msup></msub></math> signal with the relevant collider bounds. We also study an embedding of the simplified model into a three-Higgs-doublet framework and investigate its main phenomenological constraints.

Towards a viable scalar interpretation of <math><mrow><msub><mrow><mi>R</mi></mrow><mrow><msup><mrow><mi>D</mi></mrow><mrow><mo>(</mo><mo>*</mo><mo>)</mo></mrow></msup></mrow></msub></mrow></math>

There has been a steady interest in flavor anomalies and their global fits as ideal probes of new physics. If the anomalies are real, one promising explanation is a new Z′ gauge boson with a flavor-changing coupling to bottom and strange quarks and a flavor-conserving coupling to muons and, possibly, electrons. We point out that direct production of such a Z′ , emerging from the collision of b and s quarks, may offer a complementary window into these phenomena because collider searches already provide competitive constraints. On top of that, we analyze the same Z′ scenario in relation to another long-standing discrepancy between theory and experiment that concerns the anomalous magnetic moment of the muon. By scanning the allowed Z′ coupling strengths in the low-mass region, we assess the compatibility of the signals from LHCb with the Z′ searches in the high energy LHC data and the measurements of the anomalous magnetic moments of the involved leptons. We also argue that observations of the latter can break the degeneracy pattern in the Wilson coefficients C9 and C10 presented by LHCb data. The Z′ model we consider is compatible with the new measurement of RK⁎ , therefore it can potentially account for the long-standing deviations observed in B -physics.

Stefano Di Chiara

Australia

Andrew Fowlie

Minimal flavor-changing Z ′ models and muon g − 2 after the RK⁎ measurement

While dark matter self-interactions may solve several problems with structure formation, so far only the effects of two-body scatterings of dark matter particles have been considered. We show that, if a subdominant component of dark matter is charged under an unbroken U(1) gauge group, collective dark plasma effects need to be taken into account to understand its dynamics. Plasma instabilities can lead to collisionless dark matter shocks in galaxy cluster mergers which might have been already observed in the Abell 3827 and 520 clusters. As a concrete model we propose a thermally produced dark pair plasma of vector-like fermions. In this scenario the interacting dark matter component is expected to be separated from the stars and the non-interacting dark matter halos in cluster collisions. In addition, the missing satellite problem is softened, while constraints from all other astrophysical and cosmological observations are avoided.

Matti Heikinheimo

Dark matter self-interactions via collisionless shocks in cluster mergers

We present a classically scale-invariant model with a confining dark sector, which is coupled to the Standard Model through the Higgs portal. The galactic centre gamma ray excess can be explained in this model by collision-induced dark matter decays to b-quarks. We discuss the possibility to obtain the dark matter relic density through thermal freeze-out, which however requires excessive fine-tuning. We then instead focus on a freeze-in scenario and perform detailed calculations and a parameter scan. We find that the observed relic density and the gamma ray excess can be explained by a wide range of parameters in this model.

Galactic centre GeV photons from dark technicolor

The CMS Collaboration has published two different searches for new physics that contain possible hints for excesses in eejj and eÎ½jj final states. Interpreting those hints as a possible signal of a right-handed gauge boson WR with mass 2â2.5Â TeV may have profound implications for our understanding of the gauge structure of nature and Grand Unification, the scalar sector accessible at the LHC, neutrino physics, and the baryon asymmetry of the Universe. We show that this interpretation is, indeed, consistent with all existing constraints. However, before making premature claims we propose a number of cross-checks at the LHC14 that could confirm or falsify this scenario. Those include searches for a ZR resonance and the related new scalar sector around 6â7Â TeV. Additionally, large effects in top-quark spin-asymmetries in single top production are possible.