arXiv subjects

Ligong Bian

Publications and source records attributed to Ligong Bian.

At least 91 records · Page 5Linked to original sources

arXiv2018

Dark matter and electroweak phase transition in the mixed scalar dark matter model

We study the electroweak phase transition in the framework of scalar singlet-doublet mixed dark matter model, where the particle dark matter candidate is the lightest neutral Higgs that comprised of the CP-even component of inert doublet and a singlet scalar. The dark matter can be dominated by the inert doublet or singlet scalar depending on the mixing. We present several benchmark models to investigate the two situations after imposing several theoretical and experimental constraints. An additional singlet scalar and the inert doublet drive the electroweak phase transition to be strongly first order. A strong first order electroweak phase transition and a viable dark matter candidate can be accomplished in two benchmark models simultaneously, where a proper mass splitting among the neutral and charged Higgs masses is needed.

hep-ph↗

arXiv2018

From inflation to cosmological electroweak phase transition with a complex scalar singlet

In this work, we investigate the possibility to realize inflation and strong first order electroweak phase transitions(SFOEWPT) together with the relic density explanation. We studied the usual Higgs-portal real singlet dark matter model and the global U(1) breaking complex singlet model with the pseudoscalar being dark matter candidate. We focus on higher dark matter parameter regions due to the lower dark matter masses region are almost excluded by the current direct detection experiments except that of the so-called ${\it Higgs~ funnel ~regime}$ with $m_{DM}\sim m_h/2$. In both models, the SFOEWPT can occur through two-step where the magnitude of the Higgs-singlet quartic couplings can account for the Higgs or singlet inflation. The usual Higgs-portal real singlet dark matter model can not address the correct relic density together with the explanation of inflation and SFOEWPT. With the complex singlet model, the correct relic density can also be obtained simultaneously when the mixing angle $0.1<θ<0.2$ and the dark matter mass is $\sim800$ GeV.

hep-ph↗

arXiv2017

Higgs Pair Productions in the CP-violating Two-Higgs-Doublet Model

The SM-like Higgs pair productions are discussed in the framework of the general CP-violating two-Higgs-doublet model, where we find the CP-violating mixing angles can be related to the Higgs self couplings. Therefore, the future experimental searches for Higgs boson pairs can be constrained by the improved precision of the electric dipole moment measurements. Based on a series constraints of the SM-like Higgs boson signal fits, the perturbative unitarity and stability bounds to the Higgs potential, and the most recent LHC searches for the heavy Higgs bosons, we suggest a set of benchmark models for the future high-energy collider searches for the Higgs pair productions. The $e^+ e^-$ colliders operating at $\sqrt{s}=$ (500 GeV, 1 TeV) are capable of measuring the Higgs cubic self couplings of the benchmark models directly. We also estimate the cross sections of the resonance contributions to the Higgs pair productions for the benchmark models at the future LHC and SppC/Fcc-hh runs.

hep-ph↗

arXiv2017

CP violation effects in the diphoton spectrum of heavy scalars

In a class of new physics models, an extended Higgs sector and new CP-violating sources are simultaneously present in order to explain the baryon asymmetry in the Universe. The aim of this work is to study the implications of beyond the Standard Model (SM) CP violation for the searches of heavy scalars at the LHC. In particular, we focus on the diphoton channel searches in the CP-violating two-Higgs-doublet model (CPV 2HDM). To have a sizable CPV in the scalar sector, the two heavy neutral scalars in 2HDM tend to be nearly degenerate. The theoretical constraints of unitarity, perturbativity and vacuum stability are considered, which requires that the heavy scalars $M_H \lesssim 1$ TeV in a large region of the parameter space. The experimental limits are also taken into account, including the direct searches of heavy neutral scalars in the final state of the SM $h$, $W$ and $Z$ bosons, the differential $t\bar{t}$ data, those from the charged scalar sector which is implied by the oblique $T$ parameter, as well as the precise measurements of the electric dipole moments of electron and mercury. The quantum interference effects between the resonances and the SM background are crucially important for the diphoton signals, and the CPV mixing of the quasi-degenerate heavy scalars could enhance significantly the resonance peak. With an integrated luminosity of 3000 fb$^{-1}$ at the LHC, almost the whole parameter space of CPV 2HDM could be probed in the diphoton channel, and the CPV could also be directly detected via the diphoton spectrum.

hep-ph↗

arXiv2017

A minimal flavored $U(1)'$ for $B$-meson anomalies

We consider an anomaly-free $U(1)'$ model with favorable couplings to heavy flavors in the Standard Model(SM), as motivated by $B$-meson anomalies at LHCb. Taking the $U(1)'$ charge to be $Q'=y(L_μ-L_τ)+ x(B_3-L_3)$, we can explain the $B$-meson anomalies without invoking extra charged fermions or flavor violation beyond the SM. We show that there is a viable parameter space with a small $x$ that is compatible with other meson decays, tau lepton and neutrino experiments as well as the LHC dimuon searches. We briefly discuss the prospects of discovering the $Z'$ gauge boson at the LHC in the proposed model.

hep-ph↗

arXiv2017

The cancellation mechanism in the predictions of electric dipole moments

The interpretation of the baryon asymmetry of the Universe necessitates the CP violation beyond the Standard Model (SM). We present a general cancellation mechanism in the theoretical predictions of the electron electric dipole moments (EDM), quark chromo-EDMs, and Weinberg operators. A relative large CP violation in the Higgs sector is allowed by the current electron EDM constraint released by the ACME collaboration in 2013, and the recent $^{199}$Hg EDM experiment. The cancellation mechanism can be induced by the mass splitting of heavy Higgs bosons around $\sim\mathcal{O}(0.1-1)$ GeV, and the extent of the mass degeneracy determines the magnitude of the CP-violating phase. We explicate this point by investigating the CP-violating two-Higgs-doublet model and the minimal supersymmetric Standard Model. The cancellation mechanism is general when there are CP violation and mixing in the Higgs sector of new physics models. The CP-violating phases in this scenario can be excluded or detected by the projected $^{225}$Ra EDM experiments with precision reaching $\sim10^{-28}\,e\cdot{\rm cm}$, as well as the future colliders.

hep-ph↗

arXiv2016

Triple Gauge Couplings at Future Hadron and Lepton Colliders

The $WW$ production is the primary channel to directly probe the triple gauge couplings. We analyze the $e^+ e^- \rightarrow W^+ W^-$ process at the proposed Circular Electron-Positron Collider (CEPC), and find that the anomalous triple gauge couplings and relevant dimension six operators can be probed up to the order of $10^{-4}$. We also estimate constraints at the 14 TeV LHC, with both 300 fb$^{-1}$ and 3000 fb$^{-1}$ integrated luminosity from the leading lepton $p_T$ and azimuthal angle difference $Δϕ_{ll}$ in the di-lepton channel. The constrain is somewhat weaker, up to the order of $10^{-3}$. The limits on the triple gauge couplings are complementary to those on the electroweak precision observables and Higgs couplings.

hep-ph↗

arXiv2016

Higgs pair productions in the CP-violating two-Higgs-doublet model

In this work, we study the SM-like Higgs pair productions in the framework of the general CP-violating two-Higgs-doublet model. Several constraints are imposed to the model sequentially, including the SM-like Higgs boson signal fits, the precise measurements of the electric dipole moments, the perturbative unitarity and stability bounds to the Higgs potential, and the most recent LHC searches for the heavy Higgs bosons. We show how are the CP-violating mixing angles related to the Higgs cubic self couplings in this setup. Afterwards, we estimate the cross sections of the future LHC/SppC searches for the Higgs pair productions, as well as other possible decay modes for the heavy Higgs bosons.

hep-ph↗

arXiv2016

Type-III two Higgs doublet model plus a pseudoscalar confronted with $h\rightarrowμτ$, muon $g-2$ and dark matter

In this work, we introduce an extra singlet pseudoscalar into the Type-III two Higgs doublet model (2HDM) which is supposed to solve a series of problems in the modern particle-cosmology. With existence of a light pseudoscalar, the $h\rightarrowμτ$ excess measured at CMS and as well as the $(g-2)_μ$ anomaly could be simultaneously explained within certain parameter spaces that can also tolerate the data on the flavor-violating processes $τ\rightarrowμγ$ and Higgs decay gained at LHC. Within the same parameter spaces, the DM relic abundance is well accounted. Moreover, the recently observed Galactic Center gamma ray excess(GCE) is proposed to realize through dark matter(DM) pair annihilations, and in this work, the scenario of the annihilation being mediated by the pseudoscalar is also addressed.

hep-ph↗

arXiv2016

Interference Effect on Resonance Studies in Searches of Heavy Particles

The interference between resonance signal and continuum background can be either constructive or destructive, depending on the relative sign of couplings between the signal and background amplitudes. Different interference schemes lead to asymmetric distortions of the resonance line shape, which could be distinguished in experiments, when the internal resonance width is larger than the detector resolution. Interpreting the ATLAS diboson excesses by means of a toy $W'$ model as an illustrative example (though it is disfavored by the 13 TeV data), we find that the signs of resonance couplings can only be revealed in the line shape measurements up to a high confidence level at a high luminosity, which could bring us further information on the underlying theory beyond resonance searches at future lepton and hadron colliders.

hep-ph↗

arXiv2016

A hidden confining world on the 750 GeV diphoton excess

We explain the recent diphoton excesses around $750$ GeV by both ATLAS and CMS as a singlet scalar $Φ$ which couples to SM gluon and neutral gauge bosons only through higher dimensional operators. A natural explanation is that $Φ$ is a pseudo-Nambu-Goldstone boson (pNGB) which receives parity violation through anomaly if there exists a hidden strong dynamics. The singlet and other light pNGBs will decay into two SM gauge bosons and even serves as the meta-stable coloured states which can be probed in the future. By accurately measuring their relative decay and the total production rate in the future, we will learn the underlying strong dynamics parameter. The lightest baryon in this confining theory could serve as a viable dark matter candidate.

hep-ph↗

arXiv2016

Impact of a complex singlet: From dark matter to baryogenesis

With the assistance of a complex singlet, and an effective operator involving CP violations, the dark matter relic abundance and baryon asymmetry of the universe have been addressed simul- taneously. We studied the electroweak baryogenesis mechanism systematically. The electroweak phase transition analysis indicates that the strong first order phase transition takes place by one- step or two-step type due to the dynamics of the energy gap between the electroweak vacuum and the vacuum of the complex singlet. The relation between the magnitude of baryon asymmetry of the universe and the phase transition type and strength has been explored in the framework of electroweak baryogenesis.

hep-ph↗

arXiv2015

Prospects for Triple Gauge Coupling Measurements at Future Lepton Colliders and the 14 TeV LHC

The $WW$ production is the primary channel to directly probe the triple gauge couplings. We first analyze the $e^+ e^- \rightarrow W^+ W^-$ process at the future lepton collider, China's proposed Circular Electron-Positron Collider (CEPC). We use the five kinematical angles in this process to constrain the anomalous triple gauge couplings and relevant dimension six operators at the CEPC up to the order of magnitude of $10^{-4}$. The most sensible information is obtained from the distributions of the production scattering angle and the decay azimuthal angles. We also estimate constraints at the 14 TeV LHC, with both 300 fb$^{-1}$ and 3000 fb$^{-1}$ integrated luminosity from the leading lepton $p_T$ and azimuthal angle difference $Δϕ_{ll}$ distributions in the di-lepton channel. The constrain is somewhat weaker, up to the order of magnitude of $10^{-3}$. The limits on the triple gauge couplings are complementary to those on the electroweak precision observables and Higgs couplings. Our results show that the gap between sensitivities of the electroweak and triple gauge boson precision can be significantly decreased to less than one order of magnitude at the 14 TeV LHC, and that both the two sensitivities can be further improved at the CEPC.

hep-ph↗

arXiv2015

Low Scale Composite Higgs Model and 1.8 $\sim$ 2 TeV Diboson Excess

We consider a simple solution to explain the recent diboson excess observed by ATALS and CMS Collaborations in models with custodial symmetry $SU(2)_L \times SU(2)_R \rightarrow SU(2)_c$. The $SU(2)_L$ triplet vector boson $ρ$ with mass range of $1.8 \sim 2$ TeV would be produced through the Drell-Yan process with sizable diboson decay branching to account for the excess. The other $SU(2)_L \times SU(2)_R$ bidoublet axial vector boson $a$ would cancel all deviations of electroweak obervables induced by $ρ$ even if the SM fermions mix with some heavy vector like (composite) fermions which couple to $ρ$ ("non-universally partially composite"), therefore allows arbitrary couplings between each SM fermion and $ρ$. We present our model in the "General Composite Higgs" framework with $SO(5) \times U(1)_X \rightarrow SO(4) \times U(1)_X$ breaking at scale $f$ and demand the first Weinberg sum rule and positive gauge boson form factors as the theoretical constraints. We find that our model can fit the diboson excess very well if the left-handed SM light quarks, charged leptons and tops have zero, zero/moderately small and moderate/large composite components for reasonable values of $g_ρ$ and $f$. The correlation between tree level $S$ parameter and the $h \rightarrow Z γ$ suggest a large $a$ contribution to $h \rightarrow Z γ$ and it is indeed a $\mathcal{O}(1)$ effect in our parameter space which provides a strong hint for our scenario if this diboson excess is confirmed by the $13 \sim 14$ TeV LHC Run II.

hep-ph↗

arXiv2015

The interpretation for Galactic Center Excess and Electroweak Phase Transition in the NMSSM

The gamma-ray excess observed by the Fermi-LAT in the Galactic Center can be interpreted by the dark matter annihilation to $b\bar{b}$ via a light pseudoscalar in the NMSSM. It is interesting to note that the corresponding singlet scalar is useful to achieve a strongly first order phase transition required by the electroweak baryogenesis. In this paper, we investigate the possibility that the NMSSM model can simultaneously accommodate these two issues. The phase transition strength can be characterized by the vacua energy gap at zero temperature and be sufficiently enhanced by the tree-level effect in the NMSSM. We find that the annihilation of Singlino/Higgsino DM particles occurring close to the light pseudoscalar resonance is favored by the galactic center excess and the observed DM relic density, and a resulting small $κ/λ$ and a negative $A_κ$ can also lead to a successful strongly first order electroweak phase transition.

hep-ph↗

arXiv2015

Two component dark matter with multi-Higgs portals

With the assistance of two extra groups, i.e., an extra hidden gauge group $SU(2)_D$ and a global $U(1)$ group, we propose a two component dark matter (DM) model. After the symmetry $SU(2)_D\times U(1)$ being broken, we obtain both the vector and scalar DM candidates. The two DM candidates communicate with the standard model (SM) via three Higgs as multi-Higgs portals. The three Higgs are mixing states of the SM Higgs, the Higgs of the hidden sector and real part of a supplement complex scalar singlet. We study relic density and direct detection of DM in three scenarios. The resonance behaviors and interplay between the two component DM candidates are represented through investigating of the relic density in the parameter spaces of the two DMs masses. The electroweak precision parameters constrains the two Higgs portals couplings ($λ_m$ and $δ_2$). The relevant vacuum stability and naturalness problem in the parameter space of $λ_m$ and $δ_2$ are studied as well. The model could alleviate these two problems in some parameter spaces under the constraints of electroweak precision observables and Higgs indirect search.

hep-ph↗

arXiv2014

Post-ACME2013 CP-violation in Higgs Physics and Electroweak Baryogenesis

We present a class of cancellation mechanisms to suppress the total contributions of Barr-Zee diagrams to the electron electric dipole moment (eEDM). This class of mechanisms are of particular significance after the new eEDM upper limit, which strongly constrains the allowed magnitude of CP-violation in Higgs couplings and hence the feasibility of electroweak baryogenesis (EWBG), were released by the ACME collaboration in 2013. We point out: if both the CP-odd Higgs-photon-photon ($Z$ boson) and the CP-odd Higgs-electron-positron couplings are turned on, a cancellation may occur either between the contributions of a CP-mixing Higgs boson, with the other Higgs bosons being decoupled, or between the contributions of a CP-even and a CP-odd Higgs bosons. With the assistance of the cancellation mechanisms, a large CP-phase in Higgs couplings with viable electroweak baryogenesis (EWBG) is still allowed. The reopened parameter regions would be probed by the future neutron, mercury EDM measurements, and direct measurements of Higgs CP-properties at the LHC and future colliders.

hep-ph↗

arXiv2013

RGE, the naturalness problem and the understanding of the Higgs mass term

The naturalness problem might be studied on the complex two dimensional plane with the technique of dimensional regularization(DREG). The Renormalization group equation(RGE) of the Higgs mass on the plane suggests the Higgs mass approaches zero at ultraviolate (UV) scale, the scale can be Planck scale when the top quark pole mass $M_{t}=168$ GeV. The real issue of the naturalness problem in the sense of Wilsonian renormalization group method is not about quadratic divergences but the rescaling effect. The Higgs mass can be considered to be one composed mass. All terms in the lagrangian in this scenario are marginal terms and no relevant terms are left, thus no rescaling effect to cause the naturalness problem anymore. RGE of the vacuum expectation value (VEV) in the Landau gauge up to two-loop order is studied. Scale-dependent behavior of the composed Higgs mass shows that we can have one tiny Higgs mass at high energy scale, even around the Planck scale, when $M_{t}\leq170.7$ GeV.

hep-ph↗