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1. Condensate decay in a radiation dominated cosmology

   https://doi.org/10.1103/PhysRevD.111.063530  

   Cao, Shuyang; Boyanovsky, Daniel (March 2025, Physical Review D)

   Ray, Rashmi (Ed.)

   We study the decay of a homogeneous condensate of a massive scalar field of mass $m$ into massless fields in thermal equilibrium in a radiation dominated cosmology. The model is a for the nonequilibrium dynamics of a misaligned axion condensate decaying into radiation. After consistent field quantization in the cosmological background, we obtain the linearized causal equations of motion for a homogeneous condensate including the finite temperature self-energy corrections up to one loop. The dynamical renormalization group is implemented to obtain the time dependent relaxation rate that describes the decay dynamics of the condensate amplitude from stimulated emission and recombination of massless quanta in the medium. It is explicitly shown that a simple friction term in the equation of motion does not describe correctly the decay of the condensate. During the super-Hubble regime, relevant for ultralight dark matter, the condensate amplitude decays as $e^{-\frac{g^2}{10}{t}^2\ln (1/mt)}$ . In the sub-Hubble regime the amplitude decays as $e^{-\gamma (t;T(t\left)\right)/2}$ with $T\left(t\right)=T_0/a\left(t\right)$ ; therefore, the finite temperature contribution to the decay rate vanishes fast during the expansion. A main conclusion is that a phenomenological friction term is inadequate to describe the decay in the super-Hubble regime, and the decay function $\gamma \left(t\right)$ is always than that from a local friction term as a consequence of the cosmological expansion. For ultralight dark matter, the timescale, during which transient dynamics is sensitive to cosmological expansion and a local friction term is inadequate, is much longer. A friction term always the timescale of decay in the sub-Hubble case. Published by the American Physical Society2025 

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2. Measurement of the branching fraction of the decay $B^{-}\to D^0\rho (770{)}^{-}$ at Belle II

   https://doi.org/10.1103/PhysRevD.109.L111103  

   Adachi, I; Aggarwal, L; Aihara, H; Akopov, N; Aloisio, A; Anh_Ky, N; Asner, D M; Atmacan, H; Aushev, V; Aversano, M; et al (June 2024, Physical Review D)

   We measure the branching fraction of the decay $B^{-}\to D^0\rho (770{)}^{-}$ using data collected with the Belle II detector. The data contain 387 million $B\overline{B}$ pairs produced in $e^{+}{e}^{-}$ collisions at the $\mathrm{\Upsilon }\left(4S\right)$ resonance. We reconstruct $8360\pm 180$ decays from an analysis of the distributions of the $B^{-}$ energy and the $\rho (770{)}^{-}$ helicity angle. We determine the branching fraction to be $(0.939\pm 0.021\left(\mathrm{stat}\right)\pm 0.050\left(\mathrm{syst}\right))\%$ , in agreement with previous results. Our measurement improves the relative precision of the world average by more than a factor of two. Published by the American Physical Society2024 

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3. Measurement of the branching fraction and $CP$ -violating asymmetry of the decay $B^0\to {\pi }^0{\pi }^0$ using 387 million $\mathrm{\Upsilon }\left(4S\right)$ decays in Belle II data

   https://doi.org/10.1103/PhysRevD.111.L071102  

   Adachi, I; Aggarwal, L; Ahmed, H; Aihara, H; Alhakami, M; Aloisio, A; Althubiti, N; Anh_Ky, N; Asner, D M; Atmacan, H; et al (April 2025, Physical Review D)

   We measure the branching fraction and $CP$ -violating flavor-dependent rate asymmetry of $B^0\to {\pi }^0{\pi }^0$ decays reconstructed using the Belle II detector in an electron-positron collision sample containing $387\times {10}^6\mathrm{\Upsilon }\left(4S\right)$ mesons. Using an optimized event selection, we find $125\pm 20$ signal decays in a fit to background-discriminating and flavor-sensitive distributions. The resulting branching fraction is $(1.25\pm 0.23)\times {10}^{-6}$ and the $CP$ -violating asymmetry is $0.03\pm 0.30$ . Published by the American Physical Society2025 

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4. First Determination of the Spin-Parity of ${\mathrm{\Xi }}_c(3055{)}^{+,0}$ Baryons

   https://doi.org/10.1103/PhysRevLett.134.081901  

   Aaij, R; Abdelmotteleb, A_S W; Abellan_Beteta, C; Abudinén, F; Ackernley, T; Adefisoye, A A; Adeva, B; Adinolfi, M; Adlarson, P; Agapopoulou, C; et al (February 2025, Physical Review Letters)

   The ${\mathrm{\Xi }}_b^{0(-)}\to {\mathrm{\Xi }}_c\left(3055{)}^{+\left(0\right)}\right(\to D^{+\left(0\right)}\mathrm{\Lambda }){\pi }^{-}$ decay chains are observed, and the spin-parity of ${\mathrm{\Xi }}_c(3055{)}^{+\left(0\right)}$ baryons is determined for the first time. The measurement is performed using proton-proton collision data at a center-of-mass energy of $\sqrt{s}=13\mathrm{TeV}$ , corresponding to an integrated luminosity of $5.4{\mathrm{fb}}^{-1}$ , recorded by the LHCb experiment between 2016 and 2018. The spin-parity of the ${\mathrm{\Xi }}_c(3055{)}^{+\left(0\right)}$ baryons is determined to be $3/2^{+}$ with a significance of more than $6.5\sigma$ ( $3.5\sigma$ ) compared to all other tested hypotheses. The up-down asymmetries of the ${\mathrm{\Xi }}_b^{0(-)}\to {\mathrm{\Xi }}_c(3055{)}^{+\left(0\right)}{\pi }^{-}$ transitions are measured to be $-0.92\pm 0.10\pm 0.05$ ( $-0.92\pm 0.16\pm 0.22$ ), consistent with maximal parity violation, where the first uncertainty is statistical and the second is systematic. These results support the hypothesis that the ${\mathrm{\Xi }}_c(3055{)}^{+\left(0\right)}$ baryons correspond to the first $D$ -wave $\lambda$ -mode excitation of the ${\mathrm{\Xi }}_c$ flavor triplet. © 2025 CERN, for the LHCb Collaboration2025CERN 

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5. Search for New Resonances Decaying to Pairs of Merged Diphotons in Proton-Proton Collisions at $\sqrt{s}=13\mathrm{TeV}$

   https://doi.org/10.1103/PhysRevLett.134.041801  

   Hayrapetyan, A; Tumasyan, A; Adam, W; Andrejkovic, J W; Bergauer, T; Chatterjee, S; Damanakis, K; Dragicevic, M; Hussain, P S; Jeitler, M; et al (January 2025, Physical Review Letters)

   A search is presented for an extended Higgs sector with two new particles, $X$ and $\varphi$ , in the process $X\to \varphi \varphi \to \left(\gamma \gamma \right)\left(\gamma \gamma \right)$ . Novel neural networks classify events with diphotons that are merged and determine the diphoton masses. The search uses LHC proton-proton collision data at $\sqrt{s}=13\mathrm{TeV}$ collected with the CMS detector, corresponding to an integrated luminosity of $138{\mathrm{fb}}^{-1}$ . No evidence of such resonances is seen. Upper limits are set on the production cross section for $m_X$ between 300 and 3000 GeV and $m_{\varphi }/m_X$ between 0.5% and 2.5%, representing the most sensitive search in this channel. © 2025 CERN, for the CMS Collaboration2025CERN 

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