Exotic Gravitational Wave Signatures from Simultaneous Phase Transitions

We demonstrate that the relic gravitational wave background from a multi-step phase transition may deviate from the simple sum of the single spectra, for phase transitions with similar nucleation temperatures $T_N$. We demonstrate that the temperature range $\Delta T$ between the volume fractions $f(T)=0.1$ and $f(T)=0.9$ occupied by the vacuum bubbles can span $\sim 20$ GeV. This allows for a situation in which phase transitions overlap, such that the later bubbles may nucleate both in high temperature and intermediate temperature phases. Such scenarios may lead to more exotic gravitational wave spectra, which cannot be fitted that of a consecutive PTs. We demonstrate this explicitly in the singlet extension of the Standard Model. Finally, we comment on potential additional effects due to the more exotic dynamics of overlapping phase transitions.Comment: 25 pages, 7 figures. Published versio

Wess-Zumino Inflation in Light of Planck

We discuss cosmological inflation in the minimal Wess-Zumino model with a single massive chiral supermultiplet. With suitable parameters and assuming a plausible initial condition at the start of the inflationary epoch, the model can yield scalar perturbations in the Cosmic Microwave Background (CMB) of the correct strength with a spectral index n_s ~ 0.96 and a tensor-to-scalar perturbation ratio r < 0.1, consistent with the Planck CMB data. We also discuss the possibility of topological inflation within the Wess-Zumino model, and the possibility of combining it with a seesaw model for neutrino masses. This would violate R-parity, but at such a low rate that the lightest supersymmetric particle would have a lifetime long enough to constitute the astrophysical cold dark matter.Comment: 11 pages, 3 figure

Light Axion Emission and the Formation of Merging Binary Black Holes

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.Comment: 8 pages, 5 figures, reproduction package available here: https://zenodo.org/record/694967

Dark Matter Annihilation and Pair-Instability Supernovae

We study the evolution of heavy stars ($M\ge40{\rm M}_\odot$) undergoing pair-instability in the presence of annihilating dark matter. Focusing on the scenario where the dark matter is in capture-annihilation equilibrium, we model the profile of energy injections in the local thermal equilibrium approximation. We find that significant changes to masses of astrophysical black holes formed by (pulsational) pair-instability supernovae can occur when the ambient dark matter density $\rho_{\rm DM} \gtrsim10^9 \rm \, GeV \, cm^{-3}$. There are two distinct outcomes, depending on the dark matter mass. For masses $m_{\rm DM}\gtrsim1$ GeV the DM is primarily confined to the core. The annihilation increases the lifetime of core helium burning, resulting in more oxygen being formed, fueling a more violent explosion during the pair-instability-induced contraction. This drives stronger pulsations, leading to lighter black holes being formed than predicted by the standard model. For masses $m_{\rm DM}\lesssim0.5$ GeV there is significant dark matter in the envelope, leading to a phase where the star is supported by the energy from the annihilation. This reduces the core temperature and density, allowing the star to evade the pair-instability allowing heavier black holes to be formed. We find a mass gap for all models studied.Comment: Six Pages, Three Figure

Dark Matter (H)eats Young Planets

We study the effect of dark matter annihilation on the formation of Jovian planets. We show that dark matter heat injections can slow or halt Kelvin-Helmholtz contraction, preventing the accretion of hydrogen and helium onto the solid core. The existence of Jupiter in our solar system can therefore be used to infer constraints on dark matter with relatively strong interaction cross sections. In the case of spin-dependent dark matter, we derive novel constraints beyond the reach of current direct detection experiments. We highlight the possibility of a positive detection using future observations by JWST, which could reveal strongly varying planet morpholoiges close to our Galactic Center.Comment: 8 pages, 4 figures, includes astronomical observations made with the naked ey