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Systemic discrimination on the basis of gender and race, among other ascribed identities, harms minoritized people. This is a structural problem in society, and astronomy is not immune to it. Although we talk about the challenges faced by ‘women and minorities’, it is all too rare to acknowledge intersecting realities: some of us are minority women and our experiences are different from both white women and minority men, with sexism and racism compounding in nonlinear ways. Confronting the challenges associated with invoking an intersectional analysis can be daunting if the mainstream community continues to ignore helpful work from the social sciences, which can teach us new ways of understanding how we produce scientific knowledge. Rather than failing to question how science is done, we should let curiosity be our guide.

In this article I take on the question of how the exclusion of Black American women from physics impacts physics epistemologies, and I highlight the dynamic relationship between this exclusion and the struggle for women to reconcile “Black woman” with “physicist.” I describe the phenomenon where white epistemic claims about science—which are not rooted in empirical evidence—receive more credence and attention than Black women’s epistemic claims about their own lives. To develop this idea, I apply an intersectional analysis to Joseph Martin’s concept of prestige asymmetry in physics, developing the concept of white empiricism to discuss the impact that Black women’s exclusion has had on physics epistemology. By considering the essentialization of racism and sexism alongside the social construction of ascribed identities, I assess the way Black women physicists self-construct as scientists and the subsequent impact of epistemic outcomes on the science itself.

Prescod-Weinstein talks about the axion. The axion began as a solution to a problem in the Standard Model of particle physics--specifically, the part built on the theory of quantum chromodynamics (QCD), which governs the fundamental particles we call quarks and gluons. QCD is highly successful, but it predicts properties we've never seen in the neutron (which is made of quarks).

In this White Paper we present the potential of the Enhanced X-ray Timing and Polarimetry (eXTP) mission for determining the nature of dense matter; neutron star cores host an extreme density regime which cannot be replicated in a terrestrial laboratory. The tightest statistical constraints on the dense matter equation of state will come from pulse profile modelling of accretion-powered pulsars, burst oscillation sources, and rotation-powered pulsars. Additional constraints will derive from spin measurements, burst spectra, and properties of the accretion flows in the vicinity of the neutron star. Under development by an international Consortium led by the Institute of High Energy Physics of the Chinese Academy of Science, the eXTP mission is expected to be launched in the mid 2020s.

In this paper we present the science potential of the enhanced X-ray Timing and Polarimetry (eXTP) mission for studies of strongly magnetized objects. We will focus on the physics and astrophysics of strongly magnetized objects, namely magnetars, accreting X-ray pulsars, and rotation powered pulsars. We also discuss the science potential of eXTP for QED studies. Developed by an international Consortium led by the Institute of High Energy Physics of the Chinese Academy of Sciences, the eXTP mission is expected to be launched in the mid 2020s.

We introduce a modification of the PyUltraLight code that models the dynamical evolution of ultralight axionlike scalar dark matter fields. Our modified code, PySiUltraLight, adds a quartic, self-interaction term to reflect the one which arises naturally in axionlike particle models. Using a particle mass of \\(10^{-22}~\\mathrm{eV}/\\mathrm{c}^2\\), we show that PySiUltraLight produces spatially oscillating solitons, exploding solitons, and collapsing solitons which prior analytic work shows will occur with attractive self-interactions. Using our code we calculate the oscillation frequency as a function of soliton mass and equilibrium radius in the presence of attractive self-interactions. We show that when the soliton mass is below the critical mass (\\(M_c = \\frac{\\sqrt{3}}{2}M_{\\mathrm{max}}\\)) described by Chavanis [arxiv:1604.05904] and the initial radius is within a specific range, solitons are unstable and explode. We test the maximum mass criteria described by Chavanis [arxiv:1604.05904] and Chavanis and Delfini [arxiv:1103.2054] for a soliton to collapse when attractive self-interactions are included. We also analyze both binary soliton collisions and a soliton rotating around a central mass with attractive and repulsive self-interactions. We find that when attractive self-interactions are included, the density profiles get distorted after a binary collision. We also find that a soliton is less susceptible to tidal stripping when attractive self-interactions are included. We find that the opposite is true for repulsive self-interactions in that solitons would be more easily tidally stripped. Including self-interactions might therefore influence the survival timescales of infalling solitons.

As constraints on ultralight axion-like particles (ALPs) tighten, models with multiple species of ultralight ALP are of increasing interest. We perform simulations of two-ALP models with particles in the currently supported range [arXiv:1307.1705] of plausible masses. The code we modified, UltraDark.jl, not only allows for multiple species of ultralight ALP with different masses, but also different self-interactions and inter-field interactions. This allows us to perform the first three-dimensional simulations of two-field ALPs with self-interactions and inter-field interactions. Our simulations show that having multiple species and interactions introduces different phenomenological effects as compared to a single field, non-interacting scenarios. In particular, we explore the dynamics of solitons. Interacting multi-species ultralight dark matter has different equilibrium density profiles as compared to single-species and/or non-interacting ultralight ALPs. As seen in earlier work [arXiv:2011.09510], attractive interactions tend to contract the density profile while repulsive interactions spread out the density profile. We also explore collisions between solitons comprised of distinct axion species. We observe a lack of interference patterns in such collisions, and that resulting densities depend on the relative masses of the ALPs and their interactions.

Neutron stars can accumulate asymmetric dark matter (ADM) in their interiors, which affects the neutron star's measurable properties and makes compact objects prime targets to search for ADM. In this work, we use Bayesian inference to explore potential neutron star mass-radius measurements, from current and future x-ray telescopes, to constrain the bosonic ADM parameters for the case where bosonic ADM has accumulated in the neutron star interior. We find that the current uncertainties in the baryonic equation of state do not allow for constraints on the ADM parameter space to be made. However, we also find that ADM cannot be excluded and the inclusion of bosonic ADM in neutron star cores relaxes the constraints on the baryonic equation of state space. If the baryonic equation of state were more tightly constrained independent of ADM, we find that statements about the ADM parameter space could be made. In particular, we find that the high bosonic ADM particle mass (\\(m_\\chi\\)) and low effective self-interaction strength (\\(g_\\chi/m_\\phi)\\) regime is disfavored due to the observationally and theoretically motivated constraint that neutron stars must have at least a mass of \\(1 \\, \\mathrm{M_\\odot}\\). However, within the remaining parameter space, \\(m_\\chi\\) and \\(g_\\chi/m_\\phi\\) are individually unconstrained. On the other hand, the ADM mass-fraction, i.e., the fraction of ADM mass inside the neutron star, can be constrained by such neutron star measurements.

We investigate the condensation time of self-interacting axion-like particles in a gravitational well, extending the prior work [arXiv:2007.07438] which showed that the Wigner formalism is a good analytic approach to describe a condensing scalar field. In the present work, we use this formalism to affirm that \\(\\phi^4\\) self-interactions will take longer than necessary to support the time scales associated with structure formation, making gravity a necessary part of the process to bring axion dark matter into a solitonic form. Here we show that when the axions' virial velocity is taken into account, the time scale associated with self-interactions will scale as \\(\\lambda^2\\). This is consistent with recent numerical estimates, and it confirms that the Wigner formalism described in prior work~\\cite{Relax} is a helpful analytic framework to check computational work for potential numerical artifacts.