Unparticle Dark Matter

Once a parity is introduced in unparticle physics, under which unparticle provided in a hidden conformal sector is odd while all Standard Model particles are even, unparticle can be a suitable candidate for the cold dark matter (CDM) in the present universe through its coupling to the Standard Model Higgs doublet. We find that for Higgs boson mass in the range, 114.4 GeV<m_h<250 GeV, the relic abundance of unparticle with mass 50 GeV<m_U<80 GeV can be consistent with the currently observed CDM density. In this scenario, Higgs boson with mass m_h<160 GeV dominantly decays into a pair of unparticles and such an invisible Higgs boson may be discovered in future collider experiments.


Introduction
• Beyond the SM (for model buildings in this LHC era): Are there totally unexpected phenomena which has not yet discovered so far? What would be expected to happen at LHC that might be originated from some unknown models, not only SUSY or extra dimensional models, etc.? This is basically the motivation to consider about unparticle physics as a model of unexpected phenomena. • Unparticle: A hypothetical conformal hidden sector which couples to the Standard Model only through the higher dimensional operators. [H. Georgi, PRL 98, 221601 (2007)] • One concrete example: Banks-Zaks theory has a perturbative infrared (IR) fixed point [Banks and Zaks, NPB 196, 189 (1982)]. There might exist several other candidates in a gauge theory as in the SUSY QCD. Effective field theory (EFT) description of interactions between the SM and the conformal sector.
SM particles conformal sector nontrivial IR fixed point heavy particle M Integrating out the heavy particle, below the scale M U , It becomes conformal theory at low energy, which is "unparticle".

Effective field theory
• The interactions between the SM sector and the BZ fields are introduced just in an effective field theory way.
• After the dimensional transmutation at a scale , where the hidden sector goes into the conformal window, the hidden sector have to be matched onto the unparticle at the scale.
• The essential point to make lowered a cutoff scale is to have large enough anomalous dimensions for the hidden sector, and it causes a difference in each operator's dimension at UV scale and IR scale. • Imposing the spectral function to be scale invariant, it leads to the unusual behavior of the spectral function: • The most characteristic point of the unparticle is this unusual scaling raw of the spectral function.
• This spectral function corresponds to introduce the following kinetic term for the unparticle in the action.

Unparticle interactions with Z 2 parity
• We assign a Z 2 parity for which the unparticle has an odd parity, while the Standard Model particles have even parity. • The lowest operators in the SM is the Higgs mass term. So, it is natural to consider first the interaction between the unparticle and the Higgs doublet which is written by • This means that if the interaction between the Higgs doublet and the unparticle is introduced, it generically provides a 'mass' term for the unparticle after the electroweak symmetry breaking, inducing the conformal symmetry breaking. • The corresponding action is, again, given by 2007/12/14 Talk given at KEK-PH0712, KEK 7 T.K. and N. Okada, arXiv:0711.1506 [hep-ph] Conformal symmetry is broken below M Z • After developing the VEV of the Higgs doublet, conformal symmetry is broken at the weak scale, and the coupling constant in the hidden sector re-start its running.
• Then, unparticle may become much stronger below the weak scale so that it realizes a confinement in the hidden sector. Comparison with massless particles • Remember the spectral function of the unparticle: • It is impressive to compare this result of the unparticle with that of the n collections of the massless particles: • 1. SM can only explain 4% of total energy budget of universe. 2. At least, the DM should be explained in the context of the particle physics, which cannot be done within the frame of the SM.

Unparticle (?)
Unparticle interaction with Z 2 parity • The interaction between the unparticle and the Higgs boson is introduced in the following form: • After developing the VEV for the Higgs boson, the unparticle gains a mass, and after that, it can decay into the Higgs boson.
• Then the annihilation cross section can easily be calculated by considering the following diagrams. Signal is l + l − p T , with m(l + l − ) = mZ (l= e, μ) • tt + H inv [Gunion (1994)] Signal is bjj +bl+p T