arXiv subjects

Xiao-Fang Han

Publications and source records attributed to Xiao-Fang Han.

32 records · Page 2Linked to original sources

arXiv2015

A simplified 2HDM with a scalar dark matter and the galactic center gamma-ray excess

Due to the strong constrain from the LUX experiment, the scalar portal dark matter can not generally explain a gamma-ray excess in the galactic center by the annihilation of dark matter into $b\bar{b}$. With the motivation of eliminating the tension, we add a scalar dark matter to the aligned two-Higgs-doublet model, and focus on a simplified scenario, which has two main characteristics: (i) The heavy CP-even Higgs is the discovered 125 GeV Higgs boson, which has the same couplings to the gauge bosons and fermions as the SM Higgs. (ii) Only the light CP-even Higgs mediates the dark matter interactions with SM particles, which has no couplings to $WW$ and $ZZ$, but the independent couplings to the up-type quarks, down-type quarks and charged leptons. We find that the tension between $<σv>_{SS\to b\bar{b}}$ and the constraint from LUX induced by the scalar portal dark matter can go away for the isospin-violating dark matter-nucleon coupling with $-1.0< f^n/f^p<0.7$, and the constraints from the Higgs search experiments and the relic density of Planck are also satisfied.

hep-ph↗

arXiv2014

Study of the heavy CP-even Higgs with mass 125 GeV in two-Higgs-doublet models at the LHC and ILC

We assume that the 125 GeV Higgs discovered at the LHC is the heavy CP-even Higgs of the two-Higgs-doublet models, and examine the parameter space in the Type-I, Type-II, Lepton-specific and Flipped models allowed by the latest Higgs signal data, the relevant experimental and theoretical constraints. Further, we show the projected limits on $\tanβ$, $\sin(β-α)$, $Hf\bar{f}$ and $HVV$ couplings from the future measurements of the 125 GeV Higgs at the LHC and ILC, including the LHC with integrated luminosity of 300 fb$^{-1}$ (LHC-300 fb$^{-1}$) and 3000 fb$^{-1}$ (LHC-3000 fb$^{-1}$) as well as the ILC at $\sqrt{s}=250$ GeV (ILC-250 GeV), $\sqrt{s}=500$ GeV (ILC-500 GeV) and $\sqrt{s}=1000$ GeV (ILC-1000 GeV). Assuming that the future Higgs signal data have no deviation from the SM expectation, the LHC-300 fb$^{-1}$, LHC-3000 fb$^{-1}$ and ILC-1000 GeV can exclude the wrong-sign Yukawa coupling regions of the Type-II, Flipped and Lepton-specific models at the $2σ$ level, respectively. The future experiments at the LHC and ILC will constrain the Higgs couplings to be very close to SM values, especially for the $HVV$ coupling.

hep-ph↗

arXiv2014

LHC diphoton and Z+photon Higgs signals in the Higgs triplet model with Y=0

We study the implications of the LHC diphoton and Z+photon Higgs signals on the Higgs triplet model with Y=0. We discuss three different scenarios: (i) the observed boson is the light Higgs boson $h$; (ii) it is the heavy Higgs boson $H$; (iii) the observed signal is from the almost degenerate $h$ and $H$. We find that the inclusive Higgs diphoton rates in the first two scenarios can be enhanced or suppressed compared to the SM value, which can respectively fit the ATLAS and CMS diphoton data within $1σ$ range. The inclusive $ZZ^*$ rates are suppressed, which are outside $1σ$ range of ATLAS data and within $1σ$ range of CMS data. Meanwhile, another CP-even Higgs boson production rate can be suppressed enough not to be observed at the collider. For the third scenario, the Higgs diphoton rate is suppressed, which is outside $1σ$ range of ATLAS data, and the $ZZ^*$ rate equals to SM value approximately. In addition, we find that the two rates of $h\to γγ$ and $h\to Zγ$ have the positive correlations for the three scenarios.

hep-ph↗

arXiv2014

Status of the aligned two-Higgs-doublet model confronted with the Higgs data

Imposing the theoretical constraints from vacuum stability, unitarity and perturbativity as well as the experimental constraints from the electroweak precision data, flavor observables and the non-observation of additional Higgs at collider, we study the implications of available Higgs signals on a two-Higgs-doublet model with the alignment of the down-type quarks and charged lepton Yukawa coupling matrices. Compared to the four traditional types of two-Higgs-doublet models, the model has two additional mixing angles $θ_d$ and $θ_l$ in the down-type quark and charged lepton Yukawa interactions. We find that the mixing angle $θ_d$ can loose the constraints on $sin(β-α)$, $tanβ$ and $m_{H^{\pm}}$ sizably. The model can provide the marginally better fit to available Higgs signals data than SM, which requires the Higgs couplings with gauge bosons, $u\bar{u}$ and $d\bar{d}$ to be properly suppressed, and favors (1 <θ_d< 2, 0.5 <θ_l< 2.2) for $m_h=$ 125.5 GeV and (0.5 <θ_d< 2, 0.5 <θ_l< 2.2) for $m_H=$ 125.5 GeV. However, these Higgs couplings are allowed to have sizable deviations from SM for ($m_h=$ 125.5 GeV, 125.5 $\leq m_H\leq$ 128 GeV) and (125 GeV $\leq m_h\leq$ 125.5 GeV, $m_H=$ 125.5 GeV).

hep-ph↗

arXiv2013

Little Higgs theory confronted with the LHC Higgs data

We confront the little Higgs theory with the LHC Higgs search data (up to 17 fb$^{-1}$ of the combined 7 and 8 TeV run). Considering some typical models, namely the littlest Higgs model (LH), the littlest Higgs model with T-parity (LHT-A and LHT-B) and the simplest little Higgs model (SLH), we scan over the parameter space in the region allowed by current experiments. We find that in these models the inclusive and exclusive (via gluon-gluon fusion) diphoton and $ZZ^*$ signal rates of the Higgs boson are always suppressed and approach to the SM predictions for a large scale $f$. Thus, the $ZZ^*$ signal rate is within the $1σ$ range of the experimental data while the inclusive diphoton signal rate is always outside the $2σ$ range. Especially, in the LHT-A the diphoton signal rate is outside the $3σ$ range of the experimental data for $f < 800$ GeV. We also perform a global $χ^2$ fit to the available LHC and Tevatron Higgs data, and find that these models provide no better global fit to the whole data set (only for some special channels a better fit can be obtained, specially in the LHT-B).

hep-ph↗

arXiv2013

130 GeV gamma-ray line and enhancement of $h\toγγ$ in the Higgs triplet model plus a scalar dark matter

With a discrete $Z_2$ symmetry being imposed, we introduce a real singlet scalar $S$ to the Higgs triplet model with the motivation of explaining the tentative evidence for a spectral feature at $E_γ$ = 130 GeV in the Fermi LAT data. The model can naturally satisfy the experimental constraints of the dark matter relic density and direct detection data from Xenon100. The doubly charged and one charged scalars can enhance the annihilation cross section of $SS\toγγ$ via the one-loop contributions, and give the negligible contributions to the relic density. $<\sigmav>_{SS\toγγ}$ for $m_{S}=130$ GeV can reach $\ord(1)\times10^{-27} cm^3 s^{-1}$ for the small charged scalar masses and the coupling constant of larger than 1. Besides, this model also predict a second photon peak at 114 GeV from the annihilation $SS\toγZ$, and the cross section is approximately 0.76 times that of $SS\toγγ$, which is below the upper limit reported by Fermi LAT. Finally, the light charged scalars can enhance LHC diphoton Higgs rate, and make it to be consistent with the experimental data reported by ATLAS and CMS.

hep-ph↗

arXiv2012

The recent Higgs boson data and Higgs triplet model with vectorlike quarks

Some vectorlike quarks are added to the Higgs triplet model with the motivation of fitting the recent Higgs boson data released by LHC and Tevatron collaborations. These vectorlike quarks can suppress the cross section of $gg\to h$ sizably, while the charged scalars, especially for the doubly charged scalar, can enhance $Br(h\to γγ)$ more sizably. Besides, the Higgs couplings to $WW$, $ZZ$ and light fermions can be the same as their SM values. Thus, the model will enhance the Higgs production rates into $γγ$ and $jjγγ$, while those for $WW^*$, $ZZ^*$ and $τ\barτ$ at the LHC are reduced relative to their SM predictions. The Higgs production rates into $Vb\bar{b}$ at the Tevatron are the same as the SM values.

hep-ph↗

arXiv2012

LHC diphoton Higgs signal and top quark forward-backward asymmetry in quasi-inert Higgs doublet model

In the quasi-inert Higgs doublet model, we study the LHC diphoton rate for a standard model-like Higgs boson and the top quark forward-backward asymmetry at Tevatron. Taking into account the constraints from the vacuum stability, unitarity, electroweak precision tests, flavor physics and the related experimental data of top quark, we find that compared with the standard model prediction, the diphoton rate of Higgs boson at LHC can be enhanced due to the light charged Higgs contributions, while the measurement of the top quark forward-backward asymmetry at Tevatron can be explained to within $1σ$ due to the non-standard model neutral Higgs bosons contributions. Finally, the correlations between the two observables are discussed.

hep-ph↗

arXiv2011

Rare Z-decay into light pseudoscalar bosons in the simplest little Higgs model

The simplest little Higgs model predicts a light pseudoscalar boson $η$ and opens up some new decay modes for $Z$-boson, such as $Z \to \bar{f} f η$, $Z\to ηηη$, $Z\to ηγ$ and $Z\to ηgg$. We examine these decay modes in the parameter space allowed by current experiments, and find that the branching ratios can reach $10^{-7}$ for $Z\to \bar{b}bη$, $10^{-8}$ for $Z\to \barττη$, and $10^{-8}$ for $Z\to ηγ$, which should be accessible at the GigaZ option of the ILC. However, the branching ratios can reach $10^{-12}$ for $Z\to ηηη$, and $10^{-11}$ for $Z\to ηgg$, which are hardly accessible at the GigaZ option.

hep-ph↗

arXiv2010

Pseudoscalar boson and SM-like Higgs boson productions at LHC in simplest little Higgs model

In the framework of the simplest little Higgs model (SLHM), we perform a comprehensive study for the pair productions of the pseudoscalar boson η and SM-like Higgs boson h at LHC, namely gg(b\bar{b})-> ηη, gg(q\bar{q})-> ηh and gg(b\bar{b})-> hh. These production processes provide a way to probe the couplings between Higgs bosons. We find that the cross section of gg-> ηη always dominates over that of b\bar{b}-> ηη. When the Higgs boson h which mediates these two processes is on-shell, their cross sections can reach several thousand $fb$ and several hundred $fb$, respectively. When the intermediate state h is off-shell, those two cross sections are reduced by two orders of magnitude, respectively. The cross sections of gg-> ηh and q\bar{q}-> ηh are about in the same order of magnitude, which can reach $\ord{(10^2fb)}$ for a light η boson. Besides, compared with the SM prediction, the cross section of a pair of SM-like Higgs bosons production at LHC can be enhanced sizably. Finally, we briefly discuss the observable signatures of ηη, ηh and hh at the LHC, respectively.

hep-ph↗

arXiv2009

Higgs-pair Production and Decay in Simplest Little Higgs Model

In the framework of the simplest little Higgs model (SLHM), we study the production of a pair of neutral CP-even Higgs bosons at the LHC. First, we examine the production rate and find that it can be significantly larger than the SM prediction. Then we investigate the decays of the Higgs-pair and find that for a low Higgs mass their dominant decay mode is hh->ηηηη(ηis a CP-odd scalar) while hh->b\bar{b}ηηand hh->ηηWW may also have sizable ratios. Finally, we comparatively study the rates of pp-> hh -> b\bar{b}τ^+ τ^-, pp->hh->b\bar{b}γγ, and pp->hh->WWWW in the SLHM and the littlest Higgs models (LHT). We find that for a light Higgs, compared with the SM predictions, all the three rates can be sizably enhanced in the LHT but severely suppressed in the SLHM; while for an intermediately heavy Higgs, both the LHT and SLHM can enhance sizably the SM predictions.

hep-ph↗

arXiv2009

R_b Constraints on Littlest Higgs Model with T-parity

In the framework of the littlest Higgs model with T-parity (LHT), we study the contributions of the T-even and T-odd particles to the branching ratio R_b. We find that the precision data of R_b can give strong constraints on the masses of T-odd fermions.

hep-ph↗

arXiv2008

Higgs and Z-boson FCNC decays correlated with B-meson decays in littlest Higgs model with T-parity

In the littlest Higgs model with T-parity (LHT) new flavor-changing interactions between mirror fermions and the Standard Model (SM) fermions can induce various FCNC decays for B-mesons, Z-boson and Higgs boson. Since all these decays induced in the LHT model are correlated, we in this work perform a collective study for these decays, namely the Z-boson decay Z -> b s_bar, the Higgs boson decay h -> b s_bar, and the B-meson decays B -> X_s γ, B_s -> μ^+μ^- and B -> X_s μ^+ μ^-. We find that under the current experimental constraints from the B-decays, the branching ratios of both Z -> b s_bar and h -> b s_bar can still deviate from the SM predictions significantly. In the parameter space allowed by the B-decays, the branching ratio of Z -> b s_bar can be enhanced to 10^{-7} (about one order above the SM prediction) while h -> b s_bar can be much suppressed relative to the SM prediction (about one order below the SM prediction).

hep-ph↗

arXiv2007

In search of an unbiased temperature estimator for statistically poor X-ray spectra

Although commonly employed by X-ray astronomers, maximum likelihood estimators are known to be biased. In this paper we investigate the bias associated to the measure of the temperature from an X-ray thermal spectrum. We show that, in the case of low surface brightness regions, commonly adopted estimators, such as those based on chi squared and Cash statistics, return strongly biased results. We stress that this can have strong implications when measuring the temperature of cluster outer regions with current experiments. We consider various approaches to overcome this problem, the most effective is a technique which allows us to correct the bias a posteriori. Extensive montecarlo simulations show that our correction returns excellent results under different conditions.

astro-ph↗