Theory and phenomenology of two-Higgs-doublet models

The identity of dark matter is a question of central importance in both astrophysics and particle physics. In the past, the leading particle candidates were cold and collisionless, and typically predicted missing energy signals at particle colliders. However, recent progress has greatly expanded the list of well-motivated candidates and the possible signatures of dark matter. This review begins with a brief summary of the standard model of particle physics and its outstanding problems. We then discuss several dark matter candidates motivated by these problems, including WIMPs, superWIMPs, light gravitinos, hidden dark matter, sterile neutrinos, and axions. For each of these, we critically examine the particle physics motivations and present their expected production mechanisms, basic properties, and implications for direct and indirect detection, particle colliders, and astrophysical observations. Upcoming experiments will discover or exclude many of these candidates, and progress may open up an era of unprecedented synergy between studies of the largest and smallest observable length scales.

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Dark Matter Candidates from Particle Physics and Methods of Detection

The identity of dark matter is a question of central importance in both astrophysics and particle physics. In the past, the leading particle candidates were cold and collisionless, and typically predicted missing energy signals at particle colliders. However, recent progress has greatly expanded the list of well-motivated candidates and the possible signatures of dark matter. This review begins with a brief summary of the standard model of particle physics and its outstanding problems. I then discuss several dark matter candidates motivated by these problems, including weakly interacting massive particles (WIMPs), superWIMPs, light gravitinos, hidden dark matter, sterile neutrinos, and axions. For each of these, I critically examine the particle physics motivations and present their expected production mechanisms, basic properties, and implications for direct and indirect detection, particle colliders, and astrophysical observations. Upcoming experiments will discover or exclude many of these candidates, and progress may open up an era of unprecedented synergy between studies of the largest and smallest observable length scales.

Quark-Gluon Plasma

We consider a relativistic plasma containing charged chiral fermions in an external magnetic field, e.g a chirally symmetric quark-gluon plasma created in relativistic heavy ion collisions. We show that triangle anomalies imply the existence of a new type of collective gapless excitation in this system that stems from the coupling between the density waves of the electric and chiral charges; we call it ”the Chiral Magnetic Wave” (CMW). The CMW exists even in a neutral plasma, i.e. in the absence of the axial and vector chemical potentials. We demonstrate the existence of CMW and study its properties using three different approaches: i) relativistic magnetohydrodynamics; ii) dimensional reduction to (1 + 1) Sine-Gordon model, appropriate in a strong magnetic field; and iii) holographic QCD (Sakai-Sugimoto model), appropriate at strong coupling. We also briefly discuss the phenomenological implications of the CMW for heavy ion collisions.

Chiral Magnetic Wave

The Breit-Wigner enhancement of the thermally averaged annihilation cross section is shown to provide a large boost factor when the dark matter annihilation process nears a narrow resonance. We explicitly demonstrate the evolution behavior of the Breit-Wigner enhanced as the function of universe temperature for both the physical and unphysical pole cases. It is found that both of the cases can lead a large enough boost factor to explain the recent PAMELA, ATIC, and PPB-BETS anomalies. We also calculate the coupling of the annihilation process, which is useful for an appropriate model building to give the desired dark matter relic density.

Enhancement of dark matter annihilation via Breit-Wigner resonance

We study fluctuations of conserved charges including baryon number, electric charge, and strangeness as well as the correlations among these conserved charges in the $2+1$ flavor Polyakov--Nambu--Jona-Lasinio model at finite temperature. The calculated results are compared with those obtained from recent lattice calculations performed with an improved staggered fermion action at two values of the lattice cutoff with almost physical up and down quark masses and a physical value for the strange quark mass. We find that our calculated results are well consistent with those obtained in lattice calculations except for some quantitative differences for fluctuations related with strange quarks. Our calculations indicate that there is a pronounced cusp in the ratio of the quartic to quadratic fluctuations of baryon number, i.e. ${\ensuremath{\chi}}_{4}^{B}/{\ensuremath{\chi}}_{2}^{B}$, at the critical temperature during the phase transition, which confirms that ${\ensuremath{\chi}}_{4}^{B}/{\ensuremath{\chi}}_{2}^{B}$ is a useful probe of the deconfinement and chiral phase transition.

Fluctuations and correlations of conserved charges in QCD at finite temperature with effective models

We study a simple ultraviolet complete and anomaly-free Z' model based on a U(1)' gauge family symmetry without introducing extra fermions beyond the standard model. The U(1)' group is diagonal in the three-family space in which the U(1)' charges of the first and second families are the same but different from those of the third family. After spontaneous symmetry breaking and rotating to the mass eigenstates of quarks and leptons, there exist, in general, both flavor-conserving and flavor-changing couplings. In the flavor-conserving case, we use the latest dijet and dilepton search at the LHC to constrain the mass and gauge couplings of Z'. Also we show that in the flavor-changing and left–right asymmetry case, the t-channel Z' process can only contribute to part of the forward–backward asymmetry in the top quark pair production observed at the Tevatron by taking into account the constraint from the same sign top production at the LHC.

Searching for a Z′ gauge boson in an anomaly-free U(1)′ gauge family model

We study the fluctuations and correlations of conserved charges, such as the baryon number, the electric charge and the strangeness, at the finite temperature and the nonzero baryon chemical potential in an effective model. The fluctuations are calculated up to the fourth-order and the correlations to the third-order. We find that the second-order fluctuations and correlations have a peak or valley structure when the chiral phase transition takes place with the increase of the baryon chemical potential; the third-order fluctuations and correlations change their signs during the chiral phase transition; and the fourth-order fluctuations have two maxima and one minimum. We also depict contour plots of various fluctuations and correlations of conserved charges in the plane of temperature and the baryon chemical potential. It is found that higher-order fluctuations and correlations of conserved charges are superior to the second-order ones to be used to search for the critical point in heavy ion collision experiments.

Fluctuations and correlations of conserved charges near the QCD critical point

The Higgs decay H -> gamma gamma due to the virtual W-loop effect is revisited in the unitary gauge by using the symmetry-preserving and divergent-behavior-preserving loop regularization method, which is realized in the four-dimensional space-time without changing original theory. Though the one-loop amplitude of H -> gamma gamma is finite as the Higgs boson in the standard model has no direct interaction with the massless photons at tree level, it involves both tensor-type and scalar-type divergent integrals which can in general destroy the gauge invariance without imposing a proper regularization scheme to make them well-defined. As the loop regularization scheme can ensure the consistency conditions between the regularized tensor-type and scalar-type divergent irreducible loop integrals to preserve gauge invariance, we explicitly show the absence of decoupling in the limit M-W/M-H -> 0 and obtain a result agreeing exactly with the earlier one in the literature. We then clarify the discrepancy of the earlier result from the recent one obtained by R. Gastmans, S.L. Wu and T.T. Wu. The advantage of calculation in the unitary gauge becomes manifest in that the non-decoupling arises from the longitudinal contribution of the W gauge boson.

http://iopscience.iop.org/article/10.1088/0253-6102/57/3/14/pdf

Yue-Liang Wu

Papers

Enhancement of dark matter annihilation via Breit-Wigner resonance

Fluctuations and correlations of conserved charges in QCD at finite temperature with effective models

Searching for a Z′ gauge boson in an anomaly-free U(1)′ gauge family model

Fluctuations and correlations of conserved charges near the QCD critical point

Note on Higgs Decay into Two Photons H → γγ