arXiv subjects

Jiayin Gu

Publications and source records attributed to Jiayin Gu.

At least 55 records · Page 3Linked to original sources

arXiv2021

Sum Rules in the Standard Model Effective Field Theory from Helicity Amplitudes

The dispersion relation of an elastic 4-point amplitude in the forward direction leads to a sum rule that connects the low energy amplitude to the high energy observables. We perform a classification of these sum rules based on massless helicity amplitudes. With this classification, we are able to systematically write down the sum rules for the dimension-6 operators of the Standard Model Effective Field Theory (SMEFT), some of which are absent in previous literatures. These sum rules offer distinct insights on the relations between the operator coefficients in the EFT and the properties of the full theory that generates them. Their applicability goes beyond tree level, and in some cases can be used as a practical method of computing the one loop contributions to low energy observables. They also provide an interesting perspective for understanding the custodial symmetries of the SM Higgs and fermion sectors.

hep-ph↗

arXiv2020

On the future of Higgs, electroweak and diboson measurements at lepton colliders

LEP precision on electroweak measurements was sufficient not to hamper the extraction of Higgs couplings at the LHC. But the foreseen permille-level Higgs measurements at future lepton colliders might suffer from parametric electroweak uncertainties in the absence of a dedicated electroweak program. We perform a joint, complete and consistent effective-field-theory analysis of Higgs and electroweak processes. The full electroweak-sector dependence of the $e^+e^- \to WW$ production process is notably accounted for, using statistically optimal observables. Up-to-date HL-LHC projections are combined with CEPC, FCC-ee, ILC and CLIC ones. For circular colliders, our results demonstrate the importance of a new $Z$-pole program for the robust extraction of Higgs couplings. At linear colliders, we show how exploiting multiple polarizations and centre-of-mass energies is crucial to mitigate contaminations from electroweak parameter uncertainties on the Higgs physics program. We also investigate the potential of alternative electroweak measurements to compensate for the lack of direct $Z$-pole run, considering for instance radiative return to these energies. Conversely, we find that Higgs measurements at linear colliders could improve our knowledge of the $Z$ couplings to electrons.

hep-ph↗

arXiv2020

Counting statistics and microreversibility in stochastic models of transistors

Multivariate fluctuation relations are established in three stochastic models of transistors, which are electronic devices with three ports and thus two coupled currents. In the first model, the transistor has no internal state variable and particle exchanges between the ports is described as a Markov jump process with constant rates. In the second model, the rates linearly depend on an internal random variable, representing the occupancy of the transistor by charge carriers. The third model has rates nonlinearly depending on the internal occupancy. For the first and second models, finite-time multivariate fluctuation relations are also established giving insight into the convergence towards the asymptotic form of multivariate fluctuation relations in the long-time limit. For all the three models, the transport properties are shown to satisfy Onsager's reciprocal relations in the linear regime close to equilibrium as well as their generalizations holding in the nonlinear regimes farther away from equilibrium, as a consequence of microreversibility.

cond-mat.stat-mech↗

arXiv2019

Galactic Stellar Populations from Photometric Metallicity Distribution Functions

Based on Sloan Digital Sky Survey (SDSS) photometric data, Gu developed a new Monte-Carlo-based method for estimating the stellar metallicity distribution functions (MDFs). This method enables a more reliable determination of MDFs compared with the conventional polynomial-based methods. In this work, MDF determined from the method are well fit by three-Gaussian model, with peaks at ${\rm [Fe/H]}$=$-0.68$, $-1.38$, and $-1.90$, associated with the thick disk, inner halo, and outer halo, respectively. The vertical metallicity gradient within $1<Z<5\,{\rm kpc}$ is ${\rm d}\langle{\rm [Fe/H]}\rangle/{\rm d}Z\approx -0.19\,{\rm dex}\cdot{\rm kpc}^{-1}$ around $R=8.25\,{\rm kpc}$. But the mean radial gradient is almost negligible. The density profile of the thick disk is fitted with modified double exponential law decaying to a constant at far distance. The scale height and scale length thus estimated are $H\approx 1.13\,{\rm kpc}$ and $L\approx 3.63\,{\rm kpc}$, which are in consistent with the results determined from star-counts method in previous studies. The halos are described with two-axial power-law ellipsoid and the axis ratios of both inner halo and outer halo, inferred from stellar number density in $R$-$Z$ plane, are $q_{ih}\approx 0.49$ and $q_{oh}\approx 0.61$, respectively. It also manifests that the outer halo is a more spherical than inner halo. Moreover, the halo power-law indices estimated are $n_{ih}\approx 3.4$ and $n_{oh}\approx 3.1$, indicating that the stellar number density of inner halo changes more steeper than that of outer halo.

astro-ph.GA↗

arXiv2019

Precision Higgs Physics at CEPC

The discovery of the Higgs boson with its mass around 125 GeV by the ATLAS and CMS Collaborations marked the beginning of a new era in high energy physics. The Higgs boson will be the subject of extensive studies of the ongoing LHC program. At the same time, lepton collider based Higgs factories have been proposed as a possible next step beyond the LHC, with its main goal to precisely measure the properties of the Higgs boson and probe potential new physics associated with the Higgs boson. The Circular Electron Positron Collider~(CEPC) is one of such proposed Higgs factories. The CEPC is an $e^+e^-$ circular collider proposed by and to be hosted in China. Located in a tunnel of approximately 100~km in circumference, it will operate at a center-of-mass energy of 240~GeV as the Higgs factory. In this paper, we present the first estimates on the precision of the Higgs boson property measurements achievable at the CEPC and discuss implications of these measurements.

hep-ex↗

arXiv2018

Microreversibility, fluctuations, and nonlinear transport in transistors

We present a stochastic approach for charge transport in transistors. In this approach, the electron and hole densities are governed by diffusion-reaction stochastic differential equations satisfying local detailed balance and the electric field is determined with the Poisson equation. The approach is consistent with the laws of electricity, thermodynamics, and microreversibility. In this way, the signal amplifying effect of transistors is verified under their working conditions. We also perform the full counting statistics of the two electric currents coupled together in transistors and we show that the fluctuation theorem holds for their joint probability distribution. Similar results are obtained including the displacement currents. In addition, the Onsager reciprocal relations and their generalizations to nonlinear transport properties deduced from the fluctuation theorem are numerically shown to be satisfied.

cond-mat.stat-mech↗

arXiv2018

New physics implication of Higgs precision measurements

Studying the properties of the Higgs boson can be an important window to explore the physics beyond the Standard Model (SM). In this work, we present studies on the implications of the Higgs precision measurements at future Higgs Factories. We perform a global fit to various Higgs search channels to obtain the 95 % C.L. constraints on the model parameter spaces of Two Higgs Double Model (2HDM) and Minimal Supersymmetric Standard Model (MSSM). In the 2HDM, we analyze tree level effects as well as one-loop contributions from the heavy Higgs bosons. The strong constraints on $\cos(β-α)$, heavy Higgs masses and their mass splitting are complementary to direct search of the LHC as well as possible future Z pole precision measurements. For the MSSM, we study both the Higgs couplings and mass precisions. The constraints on the CP-odd Higgs mass $m_A$ and stop mass scale $m_{SUSY}$ can be complementary to the direct search of HL-LHC. We also compare the sensitivity of various future Higgs factories, namely Circular Electron Positron Collider (CEPC), Future Circular Collider (FCC)-ee and International Linear Collider (ILC).

hep-ph↗

arXiv2018

Stochastic approach and fluctuation theorem for charge transport in diodes

A stochastic approach for charge transport in diodes is developed in consistency with the laws of electricity, thermodynamics, and microreversibility. In this approach, the electron and hole densities are ruled by diffusion-reaction stochastic partial differential equations and the electric field generated by the charges is determined with the Poisson equation. These equations are discretized in space for the numerical simulations of the mean density profiles, the mean electric potential, and the current-voltage characteristics. Moreover, the full counting statistics of the carrier current and the measured total current including the contribution of the displacement current are investigated. On the basis of local detailed balance, the fluctuation theorem is shown to hold for both currents.

cond-mat.stat-mech↗

arXiv2017

A global view on the Higgs self-coupling at lepton colliders

We perform a global effective-field-theory analysis to assess the precision on the determination of the Higgs trilinear self-coupling at future lepton colliders. Two main scenarios are considered, depending on whether the center-of-mass energy of the colliders is sufficient or not to access Higgs pair production processes. Low-energy machines allow for ~40% precision on the extraction of the Higgs trilinear coupling through the exploitation of next-to-leading-order effects in single Higgs measurements, provided that runs at both 240/250 GeV and 350 GeV are available with luminosities in the few attobarns range. A global fit, including possible deviations in other SM couplings, is essential in this case to obtain a robust determination of the Higgs self-coupling. High-energy machines can easily achieve a ~20% precision through Higgs pair production processes. In this case, the impact of additional coupling modifications is milder, although not completely negligible.

hep-ph↗

arXiv2017

Optimizing Higgs factories by modifying the recoil mass

It is difficult to measure the $WW$-fusion Higgs production process ($e^+e^- \to ν\barν h$) at a lepton collider with a center of mass energy of 240-250 GeV due to its small rate and the large background from the Higgsstrahlung process with an invisible $Z$ ($e^+e^- \to hZ,\,Z\to ν\barν$). We construct a modified recoil mass variable, $m^p_{\rm recoil}$, defined using only the 3-momentum of the reconstructed Higgs particle, and show that it can better separate the $WW$-fusion and Higgsstrahlung events than the original recoil mass variable $m_{\rm recoil}$. Consequently, the $m^p_{\rm recoil}$ variable can be used to improve the overall precisions of the extracted Higgs couplings, in both the conventional framework and the effective-field-theory framework. We also explore the application of the $m^p_{\rm recoil}$ variable in the inclusive cross section measurements of the Higgsstrahlung process, while a quantitive analysis is left for future studies.

hep-ph↗

arXiv2017

Learning from Higgs Physics at Future Higgs Factories

Future Higgs factories can reach impressive precision on Higgs property measurements. In this paper, instead of conventional focus of Higgs precision in certain interaction bases, we explored its sensitivity to new physics models at the electron-positron colliders. In particular, we studied two categories of new physics models, Standard Model (SM) with a real scalar singlet extension, and Two Higgs Double Model (2HDM) as examples of weakly-interacting models, Minimal Composite Higgs Model (MCHM) and three typical patterns of the more general operator counting for strong interacting models as examples of strong dynamics. We performed a global fit to various Higgs search channels to obtain the 95% C.L. constraints on the model parameter space. In the SM with a singlet extension, we obtained the limits on the singlet-doublet mixing angle sin(theta), as well as the more general Wilson coefficients of the induced higher dimensional operators. In the 2HDM, we analyzed tree level effects in tan(beta) vs. cos(beta-alpha) plane, as well as the one-loop contributions from the heavy Higgs bosons in the alignment limit to obtain the constraints on heavy Higgs masses for different types of 2HDM. In strong dynamics models, we obtained lower limits on the strong dynamics scale. In addition, once deviations of Higgs couplings are observed, they can be used to distinguish different models. We also compared the sensitivity of various future Higgs factories, namely Circular Electron Positron Collider (CEPC), Future Circular Collider (FCC)-ee and International Linear Collider (ILC).

hep-ph↗

arXiv2017

The leptonic future of the Higgs

Precision study of electroweak symmetry breaking strongly motivates the construction of a lepton collider with center-of-mass energy of at least 240 GeV. Besides Higgsstrahlung ($e^+e^- \to hZ$), such a collider would measure weak boson pair production ($e^+e^- \to WW$) with an astonishing precision. The weak-boson-fusion production process ($e^+e^- \to ν\barν h$) provides an increasingly powerful handle at higher center-of-mass energies. High energies also benefit the associated top-Higgs production ($e^+e^-\to t\bar th$) that is crucial to constrain directly the top Yukawa coupling. The impact and complementarity of differential measurements, at different center-of-mass energies and for several beam polarization configurations, are studied in a global effective-field-theory framework. We define a "global determinant parameter" (GDP) which characterizes the overall strengthening of constraints independently of the choice of operator basis. The reach of the CEPC, CLIC, FCC-ee, and ILC designs is assessed.

hep-ph↗

arXiv2017

Exploring the nearly degenerate stop region with sbottom decays

A light stop with mass almost degenerate with the lightest neutralino has important connections with both naturalness and dark matter relic abundance. This region is also very hard to probe at colliders. In this paper, we demonstrate the potential of searching for such stop particles at the LHC from sbottom decays, focusing on two channels with final states $2\ell+E^{\rm miss}_{\rm T}$ and $1b1\ell+E^{\rm miss}_{\rm T}$. We found that, if the lightest sbottom has mass around or below 1 TeV and has a significant branching ratio to decay to stop and $W$ ($\tilde{b} \to \tilde{t}\,W$), a stop almost degenerate with neutralino can be excluded up to about 500-600 GeV at the 13 TeV LHC with $300\,{\rm fb}^{-1}$ data. The searches we propose are complementary to other SUSY searches at the LHC and could have the best sensitivity to the stop-bino coannihilation region. Since they involve final states which have already been used in LHC searches, a reinterpretation of the search results already has sensitivity. Further optimization could deliver the full potential of these channels.

hep-ph↗

arXiv2016

Kinematics of the Galactic disk from LAMOST Dwarf sample

Based on the LAMOST survey and Sloan Digital Sky Survey (SDSS), we use low-resolution spectra of 130,043 F/G-type dwarf stars to study the kinematics and metallicity properties of the Galactic disk. Our study shows that the stars with poorer metallicity and larger vertical distance from Galactic plane tend to have larger eccentricity and velocity dispersion. After separating the sample stars into likely thin-disk and thick-disk sub-sample, we find that there exits a negative gradient of rotation velocity $V_ϕ$ with metallicity [Fe/H] for the likely thin-disk sub-sample, and the thick-disk sub-sample exhibit a larger positive gradient of rotation velocity with metallicity. By comparing with model prediction, we consider the radial migration of stars appears to have influenced on the thin-disk formation. In addition, our results shows that the observed thick-disk stellar orbital eccentricity distribution peaks at low eccentricity ($e \sim 0.2$) and extends to a high eccentricity ($e \sim 0.8$). We compare this result with four thick-disk formation simulated models, and it imply that our result is consistent with gas-rich merger model.

astro-ph.GA↗

arXiv2016

A Monte-Carlo Method for Making SDSS $u$-Band Magnitude more accurate

We develop a new Monte-Carlo-based method to convert the SDSS (Sloan Digital Sky Survey) $u$-band magnitude to the SCUSS (South Galactic Cap of $u$-band Sky Survey) $u$-band magnitude. Due to more accuracy of SCUSS $u$-band measurements, the converted $u$-band magnitude becomes more accurate comparing with the original SDSS $u$-band magnitude, in particular at the faint end. The average $u$ (both SDSS and SCUSS) magnitude error of numerous main-sequence stars with $0.2<g-r<0.8$ increase as $g$-band magnitude becomes fainter. When $g=19.5$, the average magnitude error of SDSS $u$ is 0.11. When $g=20.5$, the average SDSS $u$ error is up to 0.22. However, at this magnitude, the average magnitude error of SCUSS $u$ is just half as much as that of SDSS $u$. The SDSS $u$-band magnitudes of main-sequence stars with $0.2<g-r<0.8$ and $18.5<g<20.5$ are converted, therefore the maximum average error of converted $u$-band magnitudes is 0.11. The potential application of this conversion is to derive more accurate photometric metallicity calibration from SDSS observation, especially for those distant stars. Thus, we can explore stellar metallicity distributions either in the Galactic halo or some stream stars.

astro-ph.IM↗

arXiv2016

A Monte-Carlo Method for Estimating Stellar Photometric Metallicity Distributions

Based on the Sloan Digital Sky Survey (SDSS), we develop a new monte-carlo based method to estimate the photometric metallicity distribution function (MDF) for stars in the Milky Way. Compared with other photometric calibration methods, this method enables a more reliable determination of the MDF, in particular at the metal-poor and metal-rich ends. We present a comparison of our new method with a previous polynomial-based approach, and demonstrate its superiority. As an example, we apply this method to main-sequence stars with $0.2<g-r<0.6$, $6$ kpc$<R<9$ kpc, and in different intervals in height above the plane, $|Z|$. The MDFs for the selected stars within two relatively local intervals ($0.8$ kpc$<|Z|<1.2$ kpc, $1.5$ kpc$<|Z|<2.5$ kpc) can be well-fit by two Gaussians, with peaks at [Fe/H] $\approx-0.6$ and $-1.2$ respectively, one associated with the disk system, the other with the halo. The MDFs for the selected stars within two more distant intervals ($3$ kpc$<|Z|<5$ kpc, $6$ kpc$<|Z|<9$ kpc) can be decomposed into three Gaussians, with peaks at [Fe/H] $\approx-0.6$, $-1.4$ and $-1.9$ respectively, where the two lower peaks may provide evidence for a two-component model of the halo: the inner halo and the outer halo. The number ratio between the disk component and halo component(s) decreases with vertical distance from the Galactic plane, consistent with the previous literature.

astro-ph.GA↗

arXiv2016

The Zbb Couplings at Future e+e- Colliders

Many new physics models predict sizable modifications to the SM Zbb couplings, while the corresponding measurements at LEP and SLC exhibit some discrepancy with the SM predictions. After updating the current results on the Zbb coupling constraints from global fits, we list the observables that are most important for improving the Zbb coupling constraints and estimate the expected precision reach of three proposed future e+e- colliders, CEPC, ILC and FCC-ee. We consider both the case that the results are SM-like and the one that the Zbb couplings deviate significantly from the SM predictions. We show that, if we assume the value of the Zbb couplings to be within 68% CL of the current measurements, any one of the three colliders will be able to rule out the SM with more than 99.9999% CL (5 sigma). We study the implications of the improved Zbb coupling constraints on new physics models, and point out their complementarity with the constraints from the direct search of new physics particles at the LHC, as well as with Higgs precision measurements. Our results provide a further motivation for the construction of future e+e- colliders.

hep-ph↗

arXiv2016

Beyond Higgs Couplings: Probing the Higgs with Angular Observables at Future $e^+ e^-$ Colliders

We study angular observables in the $e^+e^-\to Z H\to \ell^+ \ell^-\,b\bar{b}$ channel at future circular $e^+ e^-$ colliders such as CEPC and FCC-ee. Taking into account the impact of realistic cut acceptance and detector effects, we forecast the precision of six angular asymmetries at CEPC (FCC-ee) with center-of-mass energy $\sqrt{s} =$ 240 GeV and 5 (30) ${\rm ab}^{-1}$ integrated luminosity. We then determine the projected sensitivity to a range of operators relevant for the Higgs-strahlung process in the dimension-6 Higgs EFT. Our results show that angular observables provide complementary sensitivity to rate measurements when constraining various tensor structures arising from new physics. We further find that angular asymmetries provide a novel means of both probing BSM corrections to the $H Z γ$ coupling and constraining the "blind spot" in indirect limits on supersymmetric scalar top partners.

hep-ph↗