Chuan Ren Chen

Effective Dark Matter Model: Relic density, CDMS II, Fermi LAT and LHC

The Cryogenic Dark Matter Search recently announced the observation of two signal events with a 77% confidence level. Although statistically inconclusive, it is nevertheless suggestive. In this work we present a model-independent analysis on the implication of direct and indirect searches for the dark matter using effective operator approach. Assuming that the interactions between (scalar, fermion or vector) dark matter and the standard model are mediated by unknown new physics at the scale Λ, we examine various dimension-6 tree-level induced operators and constrain them using the current experimental data, including the WMAP data of the relic abundance, CDMS II direct detection of the spin-independent scattering, and indirect detection data (Fermi LAT cosmic gamma-ray). Finally, the LHC search is also explored.

Gamma rays and positrons from a decaying hidden gauge boson

Abstract We study a scenario that a hidden gauge boson constitutes the dominant component of dark matter and decays into the standard model particles through a gauge kinetic mixing. Interestingly, gamma rays and positrons produced from the decay of hidden gauge boson can explain both the EGRET excess of diffuse gamma rays and the HEAT anomaly in the positron fraction. The spectra of the gamma rays and the positrons have distinctive features; the absence of line emission of the gamma ray and a sharp peak in the positron fraction. Such features may be observed by the FGST and PAMELA satellites.

Phenomenology of a littlest Higgs model with T parity: Including effects of T-odd fermions

We study the collider phenomenology of a littlest Higgs model with T parity. We first stress the important role of the T-odd SU(2)-doublet fermions (introduced to make the model T-parity invariant) in high energy scattering processes, such as qq? ?WH+WH- where WH± are the T-odd partners of W bosons. Because the mass of the T-odd SU(2)-doublet fermions cannot be too heavy to be consistent with low energy data, they can be copiously produced at the CERN Large Hadron Collider (LHC). Therefore, we study the collider phenomenology of the model with emphasis on the contributions of the T-odd fermion to the production of the heavy T-parity partners (either bosons or fermions) of the usual particles at the LHC. The production cross sections and the decay branching ratios of the new heavy particles are classified and various experimental signatures are discussed.

Decaying Hidden Gauge Boson and the PAMELA and ATIC/PPB-BETS Anomalies

We show that the PAMELA anomaly in the positron fraction as well as the ATIC/PPBBETS excesses in the e − +e + flux are simultaneously explained in our scenario that a hidden U (1)H gauge boson constitutes dark matter of the Universe and decays into the standardmodel particles through a kinetic mixing with an U (1)B−L gauge boson. Interestingly, the

Higgs boson production and decay in little Higgs models with T-parity

Abstract We study Higgs boson production and decay in a certain class of little Higgs models with T-parity in which some T-parity partners of the Standard Model (SM) fermions gain their masses through Yukawa-type couplings. We find that the Higgs boson production cross section of a 120 GeV Higgs boson at the CERN LHC via gg fusion process at one-loop level could be reduced by about 45%, 35% and 20%, as compared to its SM prediction, for a relatively low new particle mass scale f = 600 , 700 and 1000 GeV, respectively. On the other hand, the weak boson fusion cross section is close to the SM value. Furthermore, the Higgs boson decay branching ratio into di-photon mode can be enhanced by about 35% in small Higgs mass region in certain case, for the total decay width of Higgs boson in the little Higgs model is always smaller than that in the SM.

Cosmic rays from leptonic dark matter

If dark matter possesses a lepton number, it is natural to expect the dark-matter annihilation and/or decay mainly produces the standard model leptons, while negligible amount of the antiproton is produced. To illustrate such a simple idea, we consider a scenario that a right-handed sneutrino dark matter decays into the standard model particles through tiny R-parity violating interactions. Interestingly enough, charged leptons as well as neutrinos are directly produced, and they can lead to a sharp peak in the predicted positron fraction. Moreover, the decay of the right-handed sneutrino also generates diffuse continuum gamma rays which may account for the excess observed by EGRET, while the primary antiproton flux can be suppressed. Those predictions on the cosmic-ray fluxes of the positrons, gamma rays and antiprotons will be tested by the PAMELA and FGST observatories.

High-energy cosmic-ray positrons from hidden-gauge-boson dark matter

Abstract We provide a scenario in which a hidden U ( 1 ) gauge boson constitutes dark matter of the Universe and decays into the standard-model particles through a kinetic mixing with an U ( 1 ) B − L gauge boson. Interestingly, our model can naturally account for the steep rise in the positron fraction recently reported by PAMELA. Moreover, we find that due to the charge assignment of U ( 1 ) B − L , only a small amount of antiprotons are produced in the decay, which is also consistent with the PAMELA and other observational data.

Dark matter and collider phenomenology of split-UED

We explicitly show that split-universal extra dimension (split-UED), a recently suggested extension of universal extra dimension (UED) model, can nicely explain recent anomalies in cosmic-ray positrons and electrons observed by PAMELA and ATIC/PPB-BETS. Kaluza-Klein (KK) dark matters mainly annihilate into leptons because the hadronic branching fraction is highly suppressed by large KK quark masses and the antiproton flux agrees very well with the observation where no excess is found. The flux of cosmic gamma-rays from pion decay is also highly suppressed and hardly detected in low energy region (E?20 GeV). Collider signatures of colored KK particles at the LHC, especially q1q1 production, are studied in detail. Due to the large split in masses of KK quarks and other particles, hard pT jets and missing ET are generated, which make it possible to suppress the standard model background and discover the signals.

Color Sextet Scalars at the CERN Large Hadron Collider

Taking a phenomenological approach, we study a color sextet scalar at the LHC. We focus on the QCD production of a color sextet pair

Double take on new physics in double Higgs boson production

{\ensuremath{\Phi}}_{6}{\overline{\ensuremath{\Phi}}}_{6}