Search for: All records

We study the impact of stellar cooling due to light axion emission on the formation and evolution of black hole binaries, via stable mass transfer and the common envelope scenario.~We find that in the presence of light axion emission, no binary black hole mergers are formed with black holes in the lower mass gap ($$M_{\rm BH} < 4 {\rm M}_\odot $$) via the common envelope formation channel.~In some systems, this happens because axions prevent Roche lobe overflow.~In others, they prevent the common envelope from being ejected.~Our results apply to axions with couplings $$ g_{a \gamma} \gtrsim 10^{-10}\, \rm GeV^{-1}$$ (to photons) or $$\alpha_{ae} \gtrsim 10^{-26} $$ (to electrons) and masses $$ m_a \ll 10 \, \rm keV$$.~Light, weakly coupled particles may therefore apparently produce a mass gap $$2 {\rm M}_\odot < M_{\rm BH} < 4 {\rm M}_\odot$$ in the LIGO/Virgo/KAGRA data, when no mass gap is present in the stellar remnant population. 

The standard model of cosmology has provided a good phenomenological description of a wide range of observations both at astrophysical and cosmological scales for several decades. This concordance model is constructed by a universal cosmological constant and supported by a matter sector described by the standard model of particle physics and a cold dark matter contribution, as well as very early-time inflationary physics, and underpinned by gravitation through general relativity. There have always been open questions about the soundness of the foundations of the standard model. However, recent years have shown that there may also be questions from the observational sector with the emergence of differences between certain cosmological probes. In this White Paper, we identify the key objectives that need to be addressed over the coming decade together with the core science projects that aim to meet these challenges. These discordances primarily rest on the divergence in the measurement of core cosmological parameters with varying levels of statistical confidence. These possible statistical tensions may be partially accounted for by systematics in various measurements or cosmological probes but there is also a growing indication of potential new physics beyond the standard model. After reviewing the principal probes used in the measurement of cosmological parameters, as well as potential systematics, we discuss the most promising array of potential new physics that may be observable in upcoming surveys. We also discuss the growing set of novel data analysis approaches that go beyond traditional methods to test physical models. These new methods will become increasingly important in the coming years as the volume of survey data continues to increase, and as the degeneracy between predictions of different physical models grows. There are several perspectives on the divergences between the values of cosmological parameters, such as the model-independent probes in the late Universe and model-dependent measurements in the early Universe, which we cover at length. The White Paper closes with a number of recommendations for the community to focus on for the upcoming decade of observational cosmology, statistical data analysis, and fundamental physics developments