Peng-Fei Yin

The 750 GeV diphoton excess at the LHC and dark matter constraints

The recent reported 750 GeV diphoton excess at the 13 TeV LHC is explained in the framework of effective field theory assuming the diphoton resonance is a scalar (pseudoscalar) particle. It is found that the large production rate and the broad width of this resonance are hard to be simultaneously explained if only visible final states are considered. Therefore an invisible decay channel to dark matter (DM) is strongly favored by the diphoton resonance with a broad width, given a large coupling of the new scalar to DM. We set constraints on the parameter space in this scenario using the results from LHC Run 1, DM relic density, and DM direct and indirect detection experiments. We find that the DM searches can exclude a large portion of the parameter regions accounting for the diphoton excess with a broad width.

Constraints and Tests of the OPERA Superluminal Neutrinos

The superluminal neutrinos detected by OPERA indicate Lorentz invariance violation (LIV) of the neutrino sector at the order of 10(-5). We study the implications of the result in this work. We find that such a large LIV implied by OPERA data will make the neutrino production process π → μ + ν(μ) kinematically forbidden for a neutrino energy greater than about 5 GeV. The OPERA detection of neutrinos at 40 GeV can constrain the LIV parameter to be smaller than 3×10(-7). Furthermore, the neutrino decay in the LIV framework will modify the neutrino spectrum greatly. The atmospheric neutrino spectrum measured by the IceCube Collaboration can constrain the LIV parameter to the level of 10(-12). The future detection of astrophysical neutrinos of galactic sources is expected to be able to give an even stronger constraint on the LIV parameter of neutrinos.

Probing light stop pairs at the LHC

In this work, we study the light stop pair signals at the LHC. We explore the supersymmetry parameter space with nonuniversal gaugino and third-generation masses at the grand unified theory scale. Recent LHC supersymmetry search results based on 35 pb(-1) and 1 fb(-1) of data are implemented to put the limits on stop pair events. The dark matter relic density and direct detection constraints are also taken into account. Detailed simulations on the signals and background for some benchmark points are performed, and it is found that the stop pair signals usually escape the LHC search if the present cut conditions are used. We also explore the potential and sensitivity of ILC to probe such scenarios. It is found that the ILC can detect them with an integrated luminosity of a few tens of fb(-1).

Pulsar interpretation for the AMS-02 result

The AMS-02 Collaboration has just published a high-precision measurement of the cosmic positron fraction e(+)/(e(-) + e(+)), which rises with energy from similar to 5 GeV to similar to 350 GeV. The result indicates the existence of primary electron/positron sources to account for the positron excess. In this work, we investigate the possibility that the nearby mature pulsars with ages of O(10(5)) yr are the primary positron sources. By fitting the data we find that the positrons from a single nearby pulsar, such as Geminga or Monogem, with the spectral index alpha similar to 2 can interpret the AMS-02 result. We also investigate the possibility that high-energy positrons are generated by multiple known pulsars in the ATNF catalogue. Such a scenario can also fit the AMS-02 data well. Future precise measurements of fine structures in the positron spectrum would be a support to the pulsar scenario.

Testing the electroweak phase transition and electroweak baryogenesis at the LHC and a circular electron-positron collider

We study the collider phenomenology of the electroweak phase transition and electroweak baryogenesis in the framework of the effective field theory. Our study shows that the effective theory using the dimension-6 operators can enforce strong first order phase transition and provide sizable CP violation to realize a successful electroweak baryogenesis. Such dimension-6 operators can induce interesting Higgs phenomenology that can be verified at colliders such as the LHC and the planning CEPC. We then demonstrate that this effective theory can originate from vectorlike quarks and the triplet Higgs.

Detecting light stop pairs in coannihilation scenarios at the LHC

In this work, we study the light stop pair signals at the Large Hadron Collider (LHC) in three coannihilation scenarios, where the neutralino can coannihilate with the stop, chargino and stau, respectively, so as to yield the desired dark matter relic density. Signatures of the first scenario can be probed at the LHC via the associated jet production processes pp -> j + (t) over tilde(t) over tilde* by tagging an energetic monojet and a large missing transverse energy. The signatures of the other two scenarios can be searched via the pair production process pp -> (t) over tilde(t) over tilde* by tagging energetic b jets in the final states and a large missing transverse energy. We find that the LHC results at 7 TeV with 5 fb(-1) of data can exclude the stop mass up to 220, 380, and 220 GeV for these three scenarios, respectively. While the 20 fb(-1) data set at 8 TeV is considered, the LHC can be expected to exclude the stop mass up to 340, 430, and 370 GeV. DOI: 10.1103/PhysRevD.87.055007

A STATISTICAL MODEL FOR THE {gamma}-RAY VARIABILITY OF THE CRAB NEBULA

A statistical scenario is proposed to explain the gamma-ray variability and flares of the Crab Nebula, which were observed recently by the Fermi/LAT. In this scenario electrons are accelerated in a series of knots, whose sizes follow a power-law distribution. These knots presumably move outward from the pulsar and have a distribution in the Doppler boost factor. The maximal electron energy is assumed to be proportional to the size of the knot. Fluctuations at the highest energy end of the overall electron distribution will result in variable gamma-ray emission via the synchrotron process in the similar to 100 MeV range. Since highly boosted larger knots are rarer than smaller knots, the model predicts that the variability of the synchrotron emission increases with the photon energy. We realize such a scenario with a Monte Carlo simulation and find that the model can reproduce both the two gamma-ray flares over a period of similar to 1 year and the monthly scale gamma-ray flux fluctuations as observed by the Fermi/LAT. The observed gamma-ray spectra in both the steady and flaring states are also well reproduced.

Explanation of the Knee-like Feature in the DAMPE Cosmic

The DArk Matter Particle Explorer (DAMPE), a space-based high precision cosmic ray detector, has just reported the new measurement of the total electron plus positron energy spectrum up to 4.6 TeV. A notable feature in the spectrum is the spectral break at

{e}^{-}+{e}^{+}

\sim 0.9

Energy Spectrum

TeV, with the spectral index softening from