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- 13.02. Yan-Chuan Cai (University of Edinburgh): Peculiar velocities in cosmology
Abstract: On large scales, peculiar velocities refer to the motions of extragalactic objects relative to the background expansion of the Universe, known as the Hubble flow. Coupled with the initial density perturbations of the Universe, peculiar velocities are influenced by the expansion history of the Universe and the strength of gravity. They encode information about the matter-energy content of the Universe and the law of gravity. I will summarise how peculiar velocities of galaxies can be observed, and what we can learn about cosmology from observing them using data from galaxy redshift surveys and the cosmic-microwave background. Slides
- 10.04. Devina Misra (IFY, NTNU): Investigating cannibalistic millisecond pulsar binaries using MESA: New constraints from pulsar spin and mass evolution
Abstract: Compact binary millisecond pulsars (MSPs) with orbital periods less than 1d are key to understanding binary evolution involving massive neutron stars (NSs). Due to the ablation of the companion by the rapidly spinning pulsar, these systems are also known as spiders and categorized into two main branches: redbacks (RBs; companion mass in the range of 0.1 to 0.5Msun) and black widows (BWs; companion mass less than 0.1 Msun ). We present models of low- and intermediate-mass X-ray binaries and compare them with observations of Galactic spiders (including the presence or absence of hydrogen lines in their optical spectra), and we constrain and quantify the interaction between the pulsar and the companion. For the first time in MESA, we also included the detailed evolution of the pulsar spin and modeled the irradiation of the companion by the pulsar wind. Efficient mass accretion onto the NS (i.e., at least 70% of the mass transferred is accreted) with an X-ray irradiated disk followed by strong irradiation of the companion can explain most of the properties of the observed spiders. Our RB evolutionary tracks continue to the BW regime, connecting the two branches of spiders. Our models explain the lack of hydrogen in some observed BWs with ultra-light companions. During accretion-induced spin up, the mass required to spin up an NS to sub-milliseconds is high enough to collapse into a black hole. Cannibalistic MSP binary formation depends heavily on the interplay between accretion onto the pulsar and pulsar wind irradiation. Our work supports earlier claims that RBs evolve into BWs. We also show that the fastest-spinning pulsars may collapse before reaching sub-millisecond spin periods. Slides
- 15.05. Hosein Gholami (TU Darmstadt): Renormalization Group Consistent Treatment of Color Superconductivity in the NJL Model
Abstract: The Nambu–Jona-Lasinio (NJL) model—and particularly its extension to color superconductivity—is a powerful framework for investigating dense quark matter. However, its reliability is limited by regularization artifacts that emerge near the cutoff energy scales. In this talk, we present a mean-field Functional Renormalization Group (FRG) approach, referred to as the RG-consistent treatment, which effectively eliminates these artifacts. Our study reveals substantial modifications to the previously established phase diagram of three-flavor, neutral, color superconducting matter within the NJL model. Notably, the RG-consistent treatment not only removes the regularization artifacts but also aligns with earlier Ginzburg-Landau analyses, suggesting the emergence of a so-called dSC phase in the melting pattern of the Color-Flavor Locked (CFL) phase. Finally, I present our recent results on the renormalized Quark-Meson-Diquark (QMD) model and compare them with those obtained via the RG-consistent treatment of the QMD framework.
- 01.10. Vittoria Vecchiotti (IFY, NTNU; INAF-OAA; TDLI): Very highthigh-energy gamma-ray and neutrino emission from hadronic interaction in compact binary millisecond pulsars
Abstract: Black widow and redback systems are millisecond pulsars in compact orbits with ultra-light and low-mass companions, respectively, collectively known as ``spider pulsars". In such systems, an intrabinary shock can form between the pulsar and the companion winds, serving as a site for particle acceleration and associated non-thermal emission. Assuming that protons can be extracted from the neutron star surface and accelerated at the intrabinary shock and/or within the pulsar wind, we model the very high-energy gamma-ray and neutrino emissions (0.1−10^3~TeV) produced through interactions with the companion wind and the companion star. We first calculate the high-energy emissions using an optimistic combination of parameters to maximize the gamma-ray and neutrino fluxes. We find that, for energetic spider pulsars with a spin-down power ≳10^35 erg s−1 and a magnetic field of ∼10^3G in the companion region, the gamma-ray emission could be detectable as point sources by CTA and LHAASO, while the neutrino emission could be detectable by the future TRIDENT detector. Finally, we build a synthetic population of these systems, compute the cumulative neutrino flux expected from spider pulsars, and compare it with the Galactic neutrino diffuse emission measured by IceCube. We find that, under realistic assumptions on the fraction of the spin-down power converted into protons, the contribution of spiders to the diffuse Galactic neutrino flux is negligible.
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