Tao Liu

We study the sensitivity of a future muon collider to exotic Higgs decays in a minimal scenario of Standard Model (SM) augmented with a light singlet scalar S . We consider the decay h → S S and S ’s subsequently decay back to SM. In particular, we focus on final states with four bottom quarks ( 4 b ), and two bottom quarks and two muons ( 2 b 2 μ ). Analyses are performed for two muon collider benchmark configurations: center-of-mass collision energy s = 3 TeV with 1 ab − 1 data and s = 10 TeV with 10 ab − 1 data. Machine-learning techniques are applied to suppress backgrounds and mitigate jet-combinatorics effects in both channels. We find that the 4 b mode could be sensitive to the branching ratio, BR ( h → S S → 4 b ) , of O ( 10 − 2 ) at 3 TeV and O ( 10 − 3 ) at 10 TeV, significantly improving upon high-luminosity LHC projections. In the Higgs-portal model with S coupling to SM only through mixing with the Higgs, the sensitivities to BR ( h → S S ) remain at the same level given O ( 1 ) branching fraction of S decaying into b -quarks. The 2 b 2 μ mode benefits from a clean dimuon resonance and can probe BR ( h → S S → 2 b 2 μ ) down to 10 − 5 level at a 10 TeV muon collider. But the sensitivity to BR ( h → S S ) will be significantly reduced due to the small branching fraction of S decaying into muons in the Higgs portal model.

A bstract: We study the leading logarithmic QCD corrections to Higgs boson pair production in the high-energy limit, which originate from soft quark exchange in the Feynman diagram and are thus suppressed by the quark mass. It is found that triangle Feynman diagrams can be analyzed in the same way as single Higgs production mediated by bottom quarks [45–47], while for diagrams of box type we cannot get an all-order result due to the many more double logarithmic structures they own. In this paper we calculate the abelian corrections at three loops for the first time after obtaining the corresponding one- and two-loop leading logarithms, which are in total agreement with the analytical results in the literature.

We present results from an all-sky search for continuous gravitational waves from individual supermassive binary black holes using the third data release of the Parkes Pulsar Timing Array (PPTA). Even though we recover a common-spectrum stochastic process, potentially induced by a nanohertz gravitational-wave background, we find no evidence of continuous waves. Therefore, we place upper limits on the gravitational-wave strain amplitude: in the most sensitive frequency range around 10 nHz, we obtain a sky-averaged 95% credibility upper limit of ≈ 7 × 10⁻¹⁵. Our search is sensitive to supermassive binary black holes with a chirp mass of ≥10⁹ M _⊙ up to a luminosity distance of 50 Mpc for our least sensitive sky direction and 200 Mpc for the most sensitive direction. This work provides at least 4 times better sensitivity in the 1–200 nHz frequency band than our last search based on the PPTA’s first data release. We expect that PPTA will continue to play a key role in detecting continuous gravitational waves in the exciting era of nanohertz gravitational-wave astronomy.

We consider the two-loop amplitude of gg → HH mediated by bottom quarks, which provides a correction of percent level at leading order in the low invariant mass region. In order to compute the corresponding master integrals, we perform an expansion for the bottom quark mass, using the method of differential equations and fixing the boundary constants by a numerical approach. The results of 177 planar master integrals which are expressed in terms of multiple polylogarithms are provided.

We study the leading logarithmic QCD corrections to Higgs pair production in the high-energy limit, which originate from soft quark exchange in the Feynman diagram and are thus suppressed by the quark mass. It is found that triangle Feynman diagrams can be analyzed in the same way as single Higgs production mediated by bottom quarks [45-47], while for diagrams of box type we cannot get an all-order result due to the many more double logarithmic structures they own. In this paper we calculate the abelian corrections at three loops for the first time after obtaining the corresponding one- and two-loop leading logarithms, which are in total agreement with the analytical results in the literature.

A distinct power-law break is apparent at m _AB ∼ 21 in the deep near-infrared PEARLS-JWST galaxy counts. The break becomes more pronounced at longer wavelengths, with the slope flattening smoothly with apparent magnitude in the shortest band used at 0.9 μm, and trending toward an increasingly broken slope by the longest wavelength passband of JWST’s Near Infrared Camera, 4.4 μm. This behaviour is remarkably well predicted by the GALFORM semi-analytical model of galaxy formation. We use the model to diagnose the origin of this behaviour. The features that are responsible for the break are (1) the inherent break in the luminosity function (LF); (2) the change in the volume element with redshift; (3) the redshift-dependent nature of the k-correction (with 1 contributing to the existence of the break and 2–3 contributing to its shape). We study the contribution to these effects by their morphology using the bulge-to-total stellar mass ratio. The way in which bulge-dominated galaxies populate the bright end of the LF while disk-dominated galaxies dominate the faint end is preserved in the galaxy number counts, with a characteristic stellar mass at a break of ∼10¹⁰ M _⊙. The shape of the number counts is mainly driven by galaxies with relatively low redshift (z ≲ 2) for a limit of m _AB ≲ 28. We give a comprehensive description of why the galaxy number counts in the near-infrared PEARLS-JWST observation look the way they do and which population of galaxies is dominant at each apparent magnitude.

Many microlensed stars discovered by JWST closely follow the winding critical curve of A370 along the “Dragon Arc” with m _AB > 26.5, which we show comprises asymptotic giant branch stars microlensed by the observed level of diffuse cluster stars, corresponding to ≃1% of the dark matter density. Most events appear along the inner edge of the critical curve, following an asymmetric band of width ≃4.5 kpc that is skewed by −0.7 ± 0.2 kpc. This asymmetry, we argue, follows from the parity difference in caustic structure inherent to microlensing that extends to higher magnification in the negative parity regions. This parity difference predicts a modest net shift of −0.04 kpc to the inside of the cluster critical curve within a narrower band of ≃1.4 kpc than observed. Adding cold-dark-matter-like subhalos of 10⁶⁻⁸ M _⊙ doubles the width, but detections are predicted to favor the outside of the critical curve, where the subhalos generate local Einstein rings, and subhalos inside the critical curve depress the magnification, reducing microlensing. Instead, the density perturbations of “wave dark matter” as a Bose–Einstein condensate (ψDM) can generate a wide band of corrugated critical curves with a large negative asymmetry. We find that a de Broglie wavelength of ≃10 pc reproduces the observed width of 4.5 kpc, with a negative skewness ≃−0.6 kpc, like the data, corresponding to a boson mass of ≃10⁻²² eV, in agreement with dwarf galaxy dynamical estimates. Independently, we also find clear asymmetry in the Jupiter Arc, with 12 microlensed stars lying along the inside of the critical curve, like the Dragon Arc.

As the planning stages for a high energy muon collider enter a more concrete era, an important question arises as to what new physics could be uncovered. A TeV-scale muon collider is also a vector boson fusion (VBF) factory with a very clean background, and as such it is a promising environment to look for new physics that couples to the electroweak (EW) sector. In this paper, we explore the ability of a future TeV-scale muon collider to search for Majorana and Dirac heavy neutral leptons (HNLs) produced via EW bosons. Employing a model-independent, conservative approach, we present an estimation of the production and decay rate of HNLs over a mass range between 200 GeV and 9.5 TeV in two benchmark collider proposals with s = 3 , 10 TeV, as well as an estimation of the dominant Standard Model (SM) background. We find that exclusion limits for the mixing between the HNLs and SM neutrinos can be as low as O ( 10 − 6 ) . Additionally, we demonstrate that a TeV-scale muon collider allows for the ability to discriminate between Majorana and Dirac type HNLs for a large range of mixing values. Published by the American Physical Society 2024