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1. The NANOGrav 15 yr Data Set: Running of the Spectral Index

   https://doi.org/10.3847/2041-8213/ad99d3  

   Agazie, Gabriella; Anumarlapudi, Akash; Archibald, Anne M; Arzoumanian, Zaven; Baier, Jeremy G; Baker, Paul T; Bécsy, Bence; Blecha, Laura; Brazier, Adam; Brook, Paul R; et al (January 2025, The Astrophysical Journal Letters)

   Abstract The NANOGrav 15 yr data provide compelling evidence for a stochastic gravitational-wave (GW) background at nanohertz frequencies. The simplest model-independent approach to characterizing the frequency spectrum of this signal consists of a simple power-law fit involving two parameters: an amplitudeAand a spectral indexγ. In this Letter, we consider the next logical step beyond this minimal spectral model, allowing for arunning(i.e., logarithmic frequency dependence) of the spectral index, ${\gamma }_{\mathrm{run}}\left(f\right)=\gamma +\beta \ln \left(f/f_{\mathrm{ref}}\right)$. We fit this running-power-law (RPL) model to the NANOGrav 15 yr data and perform a Bayesian model comparison with the minimal constant-power-law (CPL) model, which results in a 95% credible interval for the parameterβconsistent with no running, $\beta \in \left(-0.80,2.96\right)$, and an inconclusive Bayes factor, $B\left(\mathrm{RPL}\mathrm{versus}\mathrm{CPL}\right)=0.69\pm 0.01$. We thus conclude that, at present, the minimal CPL model still suffices to adequately describe the NANOGrav signal; however, future data sets may well lead to a measurement of nonzeroβ. Finally, we interpret the RPL model as a description of primordial GWs generated during cosmic inflation, which allows us to combine our results with upper limits from Big Bang nucleosynthesis, the cosmic microwave background, and LIGO–Virgo–KAGRA. 

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2. Universal trimers with p-wave interactions and the faux-Efimov effect

   https://doi.org/10.1088/1361-6455/ad987b  

   Chen, Yu-Hsin; Greene, Chris H (December 2024, Journal of Physics B: Atomic, Molecular and Optical Physics)

   Abstract An unusual class of equal massp-wave universal trimers with symmetry $L^{\mathrm{\Pi }}=1^{\pm }$is identified, for both a two-component fermionic trimer withs- andp-wave scattering length close to unitarity and for a one-component fermionic trimer atp-wave unitarity. Moreover, fermionic trimers made of atoms with two internal spin components are found for $L^{\mathrm{\Pi }}=1^{\pm }$, when thep-wave interaction between spin-up and spin-down fermions is close to unitarity and/or when the interaction between two spin-up fermions is close to thep-wave unitary limit. The universality of thesep-wave universal trimers is tested here by considering van der Waals interactions in a Lennard–Jones potential with different numbers of two-body bound states; our calculations also determine the value of the scattering volume or length where the trimer state hits zero energy and can be observed as a recombination resonance. The faux-Efimov effect appears with trimer symmetry $L^{\mathrm{\Pi }}=1^{-}$when the two fermion interactions are close top-wave unitarity and the lowest $1/R^2$coefficient gets modified, thereby altering the usual Wigner threshold law for inelastic processes involving three-body continuum channels. 

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3. Search for dark matter produced in association with a single top quark and an energetic W boson in $$\sqrt{s}=$$ 13 TeV $$pp$$ collisions with the ATLAS detector

   https://doi.org/10.1140/epjc/s10052-023-11582-z  

   Aad, G.; Abbott, B.; Abbott, D. C.; Abeling, K.; Abidi, S. H.; Aboulhorma, A.; Abramowicz, H.; Abreu, H.; Abulaiti, Y.; Hoffman, A. C.; et al (July 2023, The European Physical Journal C)

   Abstract This paper presents a search for dark matter,$$\chi $$ $\chi$, using events with a single top quark and an energeticWboson. The analysis is based on proton–proton collision data collected with the ATLAS experiment at$$\sqrt{s}=$$ $\sqrt{s}=$13 TeV during LHC Run 2 (2015–2018), corresponding to an integrated luminosity of 139 fb$$^{-1}$$ ${}^{-1}$. The search considers final states with zero or one charged lepton (electron or muon), at least oneb-jet and large missing transverse momentum. In addition, a result from a previous search considering two-charged-lepton final states is included in the interpretation of the results. The data are found to be in good agreement with the Standard Model predictions and the results are interpreted in terms of 95% confidence-level exclusion limits in the context of a class of dark matter models involving an extended two-Higgs-doublet sector together with a pseudoscalar mediator particle. The search is particularly sensitive to on-shell production of the charged Higgs boson state,$$H^{\pm }$$ $H^{\pm }$, arising from the two-Higgs-doublet mixing, and its semi-invisible decays via the mediator particle,a:$$H^{\pm } \rightarrow W^\pm a (\rightarrow \chi \chi )$$ $H^{\pm }\to W^{\pm }a(\to \chi \chi )$. Signal models with$$H^{\pm }$$ $H^{\pm }$masses up to 1.5 TeV andamasses up to 350 GeV are excluded assuming a$$\tan \beta $$ $tan\beta$value of 1. For masses ofaof 150 (250) GeV,$$\tan \beta $$ $tan\beta$values up to 2 are excluded for$$H^{\pm }$$ $H^{\pm }$masses between 200 (400) GeV and 1.5 TeV. Signals with$$\tan \beta $$ $tan\beta$values between 20 and 30 are excluded for$$H^{\pm }$$ $H^{\pm }$masses between 500 and 800 GeV. 

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4. Sharp decay rate for eigenfunctions of perturbed periodic Schrödinger operators

   https://doi.org/10.1088/1361-6544/adc653  

   Liu, Wencai; Matos, Rodrigo; Treuer, John N (April 2025, Nonlinearity)

   Abstract This paper investigates uniqueness results for perturbed periodic Schrödinger operators on ${\mathbb{Z}}^d$. Specifically, we consider operators of the form $H=-\mathrm{\Delta }+V+v$, where Δ is the discrete Laplacian, $V:{\mathbb{Z}}^d\to \mathbb{R}$is a periodic potential, and $v:{\mathbb{Z}}^d\to \mathbb{C}$represents a decaying impurity. We establish quantitative conditions under which the equation $-\mathrm{\Delta }u+Vu+vu=\lambda u$, for $\lambda \in \mathbb{C}$, admits only the trivial solution $u\equiv 0$. Key applications include the absence of embedded eigenvalues for operators with impurities decaying faster than any exponential function and the determination of sharp decay rates for eigenfunctions. Our findings extend previous works by providing precise decay conditions for impurities and analyzing different spectral regimes ofλ. 

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5. Optical and Radio Analysis of Systematically Classified Broad-lined Type Ic Supernovae from the Zwicky Transient Facility

   https://doi.org/10.3847/1538-4357/ad7fde  

   Srinivasaragavan, Gokul P; Yang, Sheng; Anand, Shreya; Sollerman, Jesper; Ho, Anna_Y Q; Corsi, Alessandra; Cenko, S Bradley; Perley, Daniel; Schulze, Steve; Sanchez-Fleming, Marquice; et al (November 2024, The Astrophysical Journal)

   Abstract We study a magnitude-limited sample of 36 broad-lined type Ic supernovae (SNe Ic-BL) from the Zwicky Transient Facility Bright Transient Survey (detected between 2018 March and 2021 August), which is the largest systematic study of SNe Ic-BL done in literature thus far. We present the light curves (LCs) for each of the SNe and analyze the shape of the LCs to derive empirical parameters, along with the explosion epochs for every event. The sample has an average absolute peak magnitude in therband of ${\overline{\mathit{M}}}_{\mathrm{r},\max }=-18.51\pm 0.15$mag. Using spectra obtained around peak light, we compute expansion velocities from the Feii5169 Å line for each event with high enough signal-to-noise ratio spectra, and find an average value of $\overline{v_{\mathrm{ph}}}=16,100\pm 1100$km s⁻¹. We also compute bolometric LCs, study the blackbody temperature and radii evolution over time, and derive the explosion properties of the SNe. The explosion properties of the sample have average values of ${\overline{\mathit{M}}}_{\mathrm{Ni}}={0.37}_{-0.06}^{+0.08}{\mathit{M}}_{\odot }$, ${\overline{\mathit{M}}}_{\mathrm{ej}}={2.45}_{-0.41}^{+0.47}{\mathit{M}}_{\odot }$, and ${\overline{\mathit{E}}}_{\mathrm{K}}=\left({4.02}_{-1.00}^{+1.37}\right)\times {10}^{51}$erg. Thirteen events have radio observations from the Very Large Array, with eight detections and five non-detections. We find that the populations that have radio detections and radio non-detections are indistinct from one another with respect to their optically inferred explosion properties, and there are no statistically significant correlations present between the events’ radio luminosities and optically inferred explosion properties. This provides evidence that the explosion properties derived from optical data alone cannot give inferences about the radio properties of SNe Ic-BL and likely their relativistic jet formation mechanisms. 

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