arXiv subjects

Qiang Li

Publications and source records attributed to Qiang Li.

612 records · Page 34Linked to original sources

arXiv2006

Critical cooling rate for the glass formation of ferromagnetic Fe40Ni40P14B6 alloy

Bulk ferromagnetic amorphous Fe-Ni-P-B alloys in rod shape were formed by a rapid solidification technique. The largest amorphous specimen prepared had a diameter of ~2.5 mm and the corresponding cooling rate for the glass formation of this alloy system in our experiment can be estimate to be around 492.4 K/s by the method of finite-difference numerical calculation. This value is on the same order of magnitude as the critical cooling rate Rc of Fe40Ni40P14B6 alloy estimated by the method of constructing the continuous-cooling-transformation (CCT) curve. It is indicated that the heterophase impurities have been eliminated well in our experiment.

cond-mat.mtrl-sci↗

arXiv2006

Formation of ferromagnetic bulk amorphous Fe40Ni40P14B6 alloys

Ferromagnetic bulk amorphous Fe40Ni40P14B6 alloy rods with a diameter of 1.2 mm can be prepared by means of a rapid quenching technique. If a fluxing technique is also used, amorphous rods with a diameter as large as 2.5 mm can be synthesized. The critical cooling rate Rc for the glass formation Fe40Ni40P14B6 is estimated to be on the order of 100 K.s-1

cond-mat.mtrl-sci↗

arXiv2006

Soft Gluon Resummation Effects in Single Graviton Production at the CERN Large Hadron Collider in the Randall-Sundrum Model

We study QCD effects in single graviton production at the CERN Large Hadron Collider (LHC) in the Randall-Sundrum (RS) Model. We present in detail the complete next-to-leading order (NLO) QCD corrections to the inclusive total cross sections. The NLO QCD corrections enhance significantly the total cross sections and decrease efficiently the dependence of the total cross sections on the factorization and renormalization scales. We also examine the uncertainty of the total cross sections due to the parton distribution function (PDF) uncertainties. For the differential cross sections on the transverse momentum ($q_T$) of the graviton, within the CSS resummation formalism, we resum the logarithmically-enhanced terms at small $q_T$ to all orders up to NLO logatithmic accuracy. Combined with the fixed order calculations, we give consistent predictions for both small $q_T$ and large $q_T$.

hep-ph↗

arXiv2006

Associated Production of Neutral Higgs Boson with Squark Pair in the Minimal Supersymmetric Standard Model with Explicit CP Violation at the CERN LHC

We investigate the associated production of neutral Higgs boson with squark pair in the minimal supersymmetric standard model with and without explicit CP violation, respectively. We show that the dominant productions in both cases are always ones of the lightest neutral Higgs boson associated with the lightest stop pair, which can reach a few pb, in the ranges of parameters allowed by constraints from the electric dipole moment experiments. In most of the parameter space, the total cross sections in the case with explicit CP violation are significantly enhanced, compared with ones without explicit CP violation. For some special parameters, several orders of magnitude enhancement can be obtained.

hep-ph↗

arXiv2005

SUSY-QCD Corrections to $W^{\pm}H^{\mp}$ Associated Production at the CERN Large Hadron Collider

We calculate the SUSY-QCD corrections to the inclusive total cross sections of the associated production processes $pp\to W^{\pm}H^{\mp}+X$ in the Minimal Supersymmetric Standard Model(MSSM) at the CERN Large Hadron Collider(LHC). The SUSY-QCD corrections can increase and decrease the total cross sections depending on the choice of the SUSY parameters. When $μ<0$ the SUSY-QCD corrections increase the leading-order (LO) total cross sections significantly for large tan$β$ ($\sim 40$), which can exceed 10% and have the opposite sign with respect to the QCD and the SUSY-EW corrections, and thus cancel with them to some extent. Moreover, we also investigate the effects of the SUSY-QCD on the differential distribution of cross sections in transverse momentum $p_T$ and rapidity Y of W-boson, and the invariant mass $M_{W^+H^-}$.

hep-ph↗

arXiv2005

Charged Higgs Production at Linear Colliders in Large Extra Dimensions

In the Two-Higgs-Doublet Model(2HDM) with large extra dimensions(LED), we study the contributions of virtual Kaluza-Klein(KK) gravitons to 2HDM charged Higgs production, especially in the two important production processes $e^+e^-\to H^+H^-$ and $e^+e^-\to H^-t\bar{b}$, at future linear colliders (LC). We find that KK graviton effects can significantly modify these total cross sections and also their differential cross sections compared to their respective 2HDM values and, therefore, can be used to probe the effective scale $Λ_T$ up to several TeV. For example, at $\sqrt{s}=2$ TeV, the cross sections for $e^+e^-\to H^+H^-$ and $e^+e^-\to H^-t\bar{b}$ in the 2HDM are 7.4fb for $m_{H^-}=150$ GeV and 0.003fb for $m_{H^-}=1.1$ TeV and $\tanβ=40$, while in LED they are 12.1fb and 0.01fb, respectively, for $Λ_T=4$ Tev.

hep-ph↗

arXiv2005

Soft Gluon Resummation Effects in Single Slepton Production at Hadron Colliders

We investigate QCD effects in the production of a single slepton at hadron colliders in the Minimal Supersymmetric Standard Model without R-parity. We calculate the total cross sections and the transverse momentum distributions at next-to-leading order in QCD. The NLO corrections enhance the total cross sections and decrease the dependence of the total cross sections on the factorization and renormalization scales. For the differential cross sections, we resum all order soft gluon effects to give reliable predictions for the transverse momentum distributions. We also compare two approaches to the non-perturbative parametrization and found that the results are slightly different at the Tevatron and are in good agreement at the LHC. Our results can be useful to the simulation of the events and to the future collider experiments.

hep-ph↗

arXiv2005

Full One-Loop Electroweak Corrections to the Charged Higgs Decays into a Chargino and Neutralino in the MSSM

We calculate the full one-loop electroweak (FEW) corrections to $H^-\to\widetildeχ^-_1\widetildeχ^0_i$ in the minimal supersymmetric standard model (MSSM), and compare with the leading order (LO) corrections including the loops of the (s)quarks only in the third generation and the complete leading order (CLO) corrections including the loops of the (s)quarks in all the three generations. We find that the magnitudes of the FEW corrections can be larger than 10% for $\tanβ>30$. Moreover, comparing with the FEW corrections, both of the LO and the CLO corrections are negligible small for the mode 1($H^-\to\widetildeχ^-_1\widetildeχ^0_1$) when $\tanβ<5$, and for the mode 2($H^-\to\widetildeχ^-_1\widetildeχ^0_2$) when $\tanβ>45$, respectively, since there are not enhancements from the Yukawa couplings. We also calculate the FEW corrections in the minimal supergravity (mSUGRA) scenario, where the FEW corrections can be larger than the LO and the CLO corrections by more than 60% and 50%, respectively.

hep-ph↗

arXiv2005

Enhanced flux pinning in YBa2Cu3O7-d films by nano-scaled substrate surface roughness

Nano-scaled substrate surface roughness is shown to strongly influence the critical current density Jc in YBCO films made by pulse-laser-deposition on the crystalline LaAlO3 substrates consisting of two separate twin-free and twin-rich regions. The nano-scaled corrugated surface was created in the twin-rich region during the deposition process. Using magneto-optical imaging techniques coupled with optical and atomic force microscopy, we observed an enhanced flux pinning in the YBCO films in the twin-rich region, resulted in \~30% increase in Jc, which was unambiguously confirmed by the direct transport measurement.

cond-mat.supr-con↗

arXiv2005

Response of fractal penetration of magnetic flux to disorder landscape in superconducting films

Magnetic flux front and induction contours in superconducting YBa2Cu3O7-d films with defect size s ~ l (superconducting coherence length) and s > l are studied by magneto-optical imaging. Robust self-affine spatial correlation was observed using scaling analysis in the small pinning-dominated (s ~ l) disorderd films. The roughness exponent was determined to be ~ 0.66, independent of numbers of defects (or the film thickness). When the disorder landscape also included a distribution of large defects (s >> l), the flux front and induction contours exhibited self-similarity, with a fractal dimension to be ~ 1.33 using the box-counting method. The remarkably different flux penetration patterns were shown to be the manifestation of self-organized criticality at different length scales.

cond-mat.supr-con↗

arXiv2005

Next-to-leading order QCD predictions for $A^0Z^0$ associated production at the CERN Large Hadron Collider

We present the calculations of the complete next-to-leading order (NLO) QCD corrections (including supersymmetric QCD) to the inclusive total cross sections of the associated production processes $pp\to A^0Z^0+X$ in the Minimal Supersymmetric Standard Model at the CERN Large Hadron Collider. Both the dimensional regularization scheme and the dimensional reduction scheme are used to organize the calculations which yield the same NLO rates. The NLO correction can either enhance or reduce the total cross sections, but it generally efficiently reduces the dependence of the total cross sections on the renormalization/factorization scale. We also examine the uncertainty of the total cross sections due to the parton distribution function uncertainties.

hep-ph↗

arXiv2005

Finite automata for testing uniqueness of Eulerian trails

We investigate the condition under which the Eulerian trail of a digraph is unique, and design a finite automaton to examine it. The algorithm is effective, for if the condition is violated, it will be noticed immediately without the need to trace through the whole trail.

cs.CC↗

arXiv2005

Next-to-leading order QCD predictions for pair production of neutral Higgs bosons at the CERN Large Hadron Collider

We present the calculations of the complete NLO inclusive total cross sections for pair production of neutral Higgs bosons through $b\bar b$ annihilation in the minimal supersymmetric standard model at the CERN Large Hadron Collider. In our calculations, we used both the DREG scheme and the DRED scheme and found that the NLO total cross sections in the above two schemes are the same. Our results show that the $b\bar b$-annihilation contributions can exceed ones of $gg$ fusion and $q\bar q$ annihilation for $h^0H^0$, $A^0h^0$ and $A^0H^0$ productions when $\tanβ$ is large. In the case of $μ>0$, the NLO corrections enhance the LO total cross sections significantly, which can reach a few tens percent, while for $μ<0$, the corrections are relatively small, and are negative in most parameter space. Moreover, the NLO QCD corrections can reduce the dependence of the total cross sections on the renormalization/factorization scale, especially for $μ<0$. We also use the CTEQ6.1 PDF sets to estimate the uncertainty of LO and NLO total cross sections, and find that the uncertainty arising from the choice of PDFs increases with the increasing $m_{A^0}$.

hep-ph↗

arXiv2005

Effects of R-parity violation in unpolarized top quark decay into polarized W-boson

We calculate one-loop R-parity violating corrections to the top quark decay into a bottom quark and a polarized W-gauge boson. The corrections are presented according to the total corrections, the longitudinal corrections and the transverse corrections, respectively. We compared our results with the ${\cal O}(α_s)$ QCD corrections, the ${\cal O}(α)$ electroweak (EW) and finite width corrections, and also the supersymmetric (SUSY) corrections with R-parity conservation, respectively.

hep-ph↗

arXiv2004

Electron scattering dependence of dendritic magnetic instability in superconducting MgB2 films

Magnetic instability in both ultra-pure and carbon-doped MgB2 films is investigated by magneto-optical imaging, transport and bulk magnetization measurements. In the carbon-doped MgB2 thin film, familiar dendritic flux-jump patterns were observed at low temperature as reported in previous experiments. In the ultra-pure MgB2 thin film, however, a remarkably stable flux penetration was observed, clearly showing the classic behavior of the critical state model. Such different behavior indicates that the electron scattering ultimately controls the magnetic stability of MgB2 films.

cond-mat.supr-con↗

arXiv2004

Effects of R-parity Violation on the Charged Higgs Boson Decays

We calculate one-loop R-parity-violating couplings corrections to the processes $H^-\to τ\bar{ν_τ}$ and $H^-\to b\bar{t}$. We find that the corrections to the $H^-\to τ\bar{ν_τ}$ decay mode are generally about 0.1%, and can be negligible. But the corrections to the $H^-\to b\bar{t}$ decay mode can reach a few percent for the favored parameters.

hep-ph↗

arXiv2002

Supersymmetric Electroweak Corrections to Heavier Top Squark Decay into Lighter Top Squark and Neutral Higgs Boson

We calculate the Yukawa corrections of order ${\cal O}(α_{ew}m_{t(b)}^2/m_W^2)$, ${\cal O}(α_{ew}m_{t(b)}^3/m_W^3)$ and ${\cal O}(α_{ew}m_{t(b)}^4/m_W^4)$ to the widths of the decays $\tilde t_2\to \tilde t_1 + (h^0,H^0,A^0)$ in the Minimal Supersymmetric Standard Model, and perform a detailed numerical analysis. We also compare the results with the ones presented in an earlier literature, where the ${\cal O}(α_{s})$ SUSY-QCD corrections to the same three decay processes have been calculated. Our numerical results show that for the decays $\tilde t_2\to \tilde t_1 + h^{0}$, $\tilde t_2\to \tilde t_1 + H^{0}$, the Yukawa corrections are significant in most of the parameter range, which can reach a few ten percent, and for the decay $\tilde t_2\to\tilde t_1 + A^{0}$, the Yukawa corrections are relatively smaller, which are only a few percent. The numerical calculations also show that using the running quark masses and the running trilinear coupling $A_t$, which include the QCD, SUSY-QCD, SUSY-Electroweak effects and resume all high order ($\tanβ$)-enhanced effects, can vastly improve the convergence of the perturbation expansion. We also discuss the effects of the running of the higgsino mass parameter $μ$ on the corrections, and find that they are significant, too, especially for large $\tanβ$.

hep-ph↗

arXiv2001

Superconducting properties of nanocrystalline MgB$_2$ thin films made by an in situ annealing process

We have studied the structural and superconducting properties of MgB$_2$ thin films made by pulsed laser deposition followed by in situ annealing. The cross-sectional transmission electron microscopy reveals a nanocrystalline mixture of textured MgO and MgB$_2$ with very small grain sizes. A zero-resistance transition temperature ($T_{c0}$) of 34 K and a zero-field critical current density ($J_c$) of $1.3 \times 10^6$ A/cm$^2$ were obtained. The irreversibility field was $\sim$ 8 T at low temperatures, although severe pinning instability was observed. These bulk-like superconducting properties show that the in situ deposition process can be a viable candidate for MgB$_2$ Josephson junction technologies.

cond-mat.mtrl-sci↗