CAPA Journal Club

26 May 2026, 13:00 → 7 Jul 2026, 14:00 Europe/Madrid

Sala Seminarios Fis. Teórica (F. Ciencias)

Tuesday 26 May

13:00 → 14:00 Magnetic Turbulence Boosts Supernova Signals of Axion-Photon Conversion

Magnetic fields between a supernova (SN) and Earth convert axions into gamma rays. The absence of such a signal in coincidence with SN 1987A neutrinos, using the coherent Milky Way field, provides well-studied constraints on $g_{ap}\times g_{a\gamma}$ (axion-proton times axion-photon couplings) and on gaγ alone. We show that the small-scale power of the turbulent magnetic field component boosts axion–photon conversion and, crucially, extends sensitivity to larger masses. The turbulent field components of the Milky Way and of the Large Magellanic Cloud (hosting SN 1987A) yield improvements of up to two orders of magnitude in $g_{ap}\times g_{a\gamma}$. Turbulence should likely impact the sensitivity of other searches based on other axion-photon conversion sites, such as starburst galaxies.

Speaker: Francesca Lecce (Bari U. & CAPA, U. Zaragoza)

2605.15261

Tuesday 9 June

13:00 → 14:00 Hawking area law in quantum gravity

We show that the LIGO--Virgo--KAGRA (LVK) verification of Hawking area law carries profound consequences for quantum gravity if such a law is postulated to hold exactly. The observed mergers can be produced in local Stelle gravity and in nonlocal quantum-gravity theories with entire or fractional form factors either by (i) singular Ricci-flat black holes or (ii) possibly regular classical black holes under very restrictive conditions: absence of $R^2$ and (Riemann)${}^2$ terms in the action, absence of extra real poles in the graviton propagator, and positivity of its spectral representation. To date, this is the strongest simplification of the ambiguities of this class of theories. We also prove that the classical standard black-hole entropy-area law holds as a consequence of Hawking area law, and provide a rigorous realization of Barrow's fractal black holes otherwise.

Speaker: Carlos Aguilar Abad (CAPA, U. Zaragoza)

2604.18669

Tuesday 7 July

13:00 → 14:00 Large Hadronic Effects in $B\to K_{\star}\mu^+\mu^-$?

Recent results from LHCb have confirmed the long-standing $P^\prime_5$ anomaly, an intriguing discrepancy in the angular distribution of the $B\to K_{\star}\mu^+\mu^-$ decay that might be a sign of new physics. In addition, the new results hint at a non-zero value for $S_7$, another observable that characterizes the $B\to K_{\star}\mu^+\mu^-$ angular distribution. We stress that a non-zero $S_7$ cannot be explained by heavy new physics but instead necessarily requires a sizable hadronic effect that introduces a strong phase. We argue that, under plausible assumptions, the hadronic effect is of the correct size to also explain $P^\prime_5$. The direct $CP$ asymmetry in $B\to K_{\star}\mu^+\mu^-$ emerges in principle as a clean probe of new physics in such a scenario. We show that a combined fit of hadronic parameters and Wilson coefficients retains sensitivity to new physics and we find strong bounds on imaginary parts of new physics Wilson coefficients.

Speaker: Alejandro Mir Ramos (CAPA, U. Zaragoza)

2512.18053 (Exp., LHCB Collab.)

2603.27753 (Theory)