Yongcheng Wu

Bio: Yongcheng Wu is an academic researcher from Carleton University. The author has contributed to research in topics: Higgs boson & Electroweak interaction. The author has an hindex of 14, co-authored 40 publications receiving 456 citations.

Electroweak precision fit and new physics in light of the W boson mass

Abstract: The W boson mass is one of the most important electroweak precision observables for testing the Standard Model or its extensions. The very recent measured W boson mass at CDF shows about 7 σ deviations from the SM prediction, which may challenge the internal consistency of the SM. By performing the global electroweak fit with the new W boson, we present the new values of the oblique parameters: S = 0 . 06 ± 0 . 10, T = 0 . 11 ± 0 . 12, U = 0 . 13 ± 0 . 09, or S = 0 . 14 ± 0 . 08, T = 0 . 26 ± 0 . 06 with U = 0 and the corresponding correlation matrices, which strongly indicates the need for the non-degenerate multiplets beyond the SM. As a proof-of-concept, we show that the new results can be accommodated in the two-Higgs doublet model, where the charged Higgs boson has to be either heavier or lighter than both two heavy neutral Higgs bosons. Therefore, searching for these non-SM Higgs bosons will provide a complementary way to test the new physics for the W boson mass anomaly.

Electroweak phase transition with composite Higgs models: calculability, gravitational waves and collider searches

Abstract: We study the strong first order electroweak phase transition (SFOEWPT) with the SO(6)/SO(5) composite Higgs model, whose scalar sector contains one Higgs doublet and one real singlet. Six benchmark models are built with fermion embeddings in 1, 6, and 15 of SO(6). We show that SFOEWPT cannot be triggered under the minimal Higgs potential hypothesis, which assumes the scalar potential is dominated by the form factors from the lightest composite resonances. To get a SFOEWPT, the contributions from local operators induced by physics above the cutoff scale are needed. We take the 6 + 6 model as an example to investigate the gravitational waves prediction and the related collider phenomenology.

Type-II 2HDM under the precision measurements at the Z-pole and a Higgs factory

Abstract: Future precision measurements of the Standard Model (SM) parameters at the proposed Z-factories and Higgs factories may have significant impacts on new physics beyond the Standard Model in the electroweak sector. We illustrate this by focusing on the Type-II two Higgs doublet model (Type-II 2HDM). The contributions from the heavy Higgs bosons at the tree-level and at the one-loop level are included in a full model parameter space. We perform a multiple variable global fit and study the extent to which the parameters of non-alignment and non-degenerate masses can be probed by the precision measurements. We find that the allowed parameter ranges are tightly constrained by the future Higgs precision measurements, especially for small and large values of tan β. Indirect limits on the masses of heavy Higgs can be obtained, which can be complementary to the direct searches of the heavy Higgs bosons at hadron colliders. We also find that the expected accuracies at the Z-pole and at a Higgs factory are quite complementary in constraining mass splittings of heavy Higgs bosons. The typical results are | cos(β − α)| < 0.008, |ΔmΦ| < 200 GeV, and tan β ∼ 0.2 − 5. The reaches from CEPC, FCC-ee and ILC are also compared, for both Higgs and Z-pole precision measurements.

The W boson Mass and Muon g − 2: Hadronic Uncertainties or New Physics?

Abstract: There are now two single measurements of precision observables that have major anomalies in the Standard Model: the recent CDF measurement of the W mass shows a 7 σ deviation and the Muon g − 2 experiment at FNAL confirmed a long-standing anomaly, implying a 4 . 2 σ deviation. Doubts regarding new physics interpretations of these anomalies could stem from uncertainties in the common hadronic contributions. We demonstrate that the two anomalies pull the hadronic contributions in opposite directions by performing electroweak fits in which the hadronic contribution was allowed to float. The fits show that including the g − 2 measurement worsens the tension with the CDF measurement and conversely that adjustments that alleviate the CDF tension worsen the g − 2 tension beyond 5 σ . This means that if we adopt the CDF W boson measurement, the case for new physics is inescapable regardless of the size of the SM hadronic contributions. Lastly, we demonstrate that a mixed scalar leptoquark extension of the Standard Model could explain both anomalies simultaneously. W boson mass from LEP [32], LHCb [33], ATLAS [34], D0 [35] and CDF [1, 31, 36]. We show an SM prediction [37], the previous PDG combination of measurements [38], CDF combinations of Tevatron and LEP measurements [1], and a simple combination that includes the new measurement, which is explained in the supplemental material. The PDG combination includes uncorrected CDF measurements. The code to reproduce this figure is available at (cid:135) . the procedure simple combination of M W the transformation HVP µ

Neutrino Portal to FIMP Dark Matter with an Early Matter Era

Abstract: We study the freeze-in production of Feebly Interacting Massive Particle (FIMP) dark matter candidates through a neutrino portal. We consider a hidden sector comprised of a fermion and a complex scalar, with the lightest one regarded as a FIMP candidate. We implement the Type-I Seesaw mechanism for generating the masses of the Standard Model (SM) neutrinos by introducing three heavy neutrinos which are assumed to be degenerated, for simplicity, and are also responsible for mediating the interactions be- tween the hidden and the SM sectors. We assume that an early matter-dominated (EMD) era took place for some period between inflation and Big Bang Nucleosynthesis, making the Universe to expand faster than in the standard radiation-dominated era. In this case, the hidden and SM sectors are easily decoupled and larger couplings between FIMPs and SM particles are needed from the relic density constraints. In this context, we discuss the dynamics of dark matter throughout the modified cosmic history, evaluate the relevant constraints of the model and discuss the consequences of the duration of the EMD era for the dark matter production. Finally, we show that if the heavy neutrinos are not part of the thermal bath, this scenario becomes testable through indirect detection searches.

The Observation of Gravitational Waves from a Binary Black Hole Merger

Abstract: On September 14, 2015 at 09:50:45 UTC the two detectors of the Laser Interferometer Gravitational-Wave Observatory simultaneously observed a transient gravitational-wave signal. The signal sweeps upwards in frequency from 35 to 250 Hz with a peak gravitational-wave strain of 1.0×10(-21). It matches the waveform predicted by general relativity for the inspiral and merger of a pair of black holes and the ringdown of the resulting single black hole. The signal was observed with a matched-filter signal-to-noise ratio of 24 and a false alarm rate estimated to be less than 1 event per 203,000 years, equivalent to a significance greater than 5.1σ. The source lies at a luminosity distance of 410(-180)(+160) Mpc corresponding to a redshift z=0.09(-0.04)(+0.03). In the source frame, the initial black hole masses are 36(-4)(+5)M⊙ and 29(-4)(+4)M⊙, and the final black hole mass is 62(-4)(+4)M⊙, with 3.0(-0.5)(+0.5)M⊙c(2) radiated in gravitational waves. All uncertainties define 90% credible intervals. These observations demonstrate the existence of binary stellar-mass black hole systems. This is the first direct detection of gravitational waves and the first observation of a binary black hole merger.

Parton distributions for the LHC

Abstract: We present a preliminary set of updated NLO parton distributions. For the first time we have a quantitative extraction of the strange quark and antiquark distributions and their uncertainties determined from CCFR and NuTeV dimuon cross sections. Additional jet data from HERA and the Tevatron improve our gluon extraction. Lepton asymmetry data and neutrino structure functions improve the flavour separation, particularly constraining the down quark valence distribution.

Detecting gravitational waves from cosmological phase transitions with LISA: an update

Abstract: We investigate the potential for observing gravitational waves from cosmological phase transitions with LISA in light of recent theoretical and experimental developments. Our analysis is based on current state-of-the-art simulations of sound waves in the cosmic fluid after the phase transition completes. We discuss the various sources of gravitational radiation, the underlying parameters describing the phase transition and a variety of viable particle physics models in this context, clarifying common misconceptions that appear in the literature and identifying open questions requiring future study. We also present a web-based tool, PTPlot, that allows users to obtain up-to-date detection prospects for a given set of phase transition parameters at LISA.