Forbidden Channels and SIMP Dark Matter

In this review, we focus on dark matter production from thermal freeze-out with forbidden channels and SIMP processes. We show that forbidden channels can be dominant to produce dark matter depending on the dark photon and / or dark Higgs mass compared to SIMP.Comment: 5 pages, Prepared for the proceedings of the 13th International Conference on Gravitation, 3-7 July 201

On thermal production of self-interacting dark matter

We consider thermal production mechanisms of self-interacting dark matter in models with gauged $Z_3$ symmetry. A complex scalar dark matter is stabilized by the $Z_3$, that is the remnant of a local dark $U(1)_d$. Light dark matter with large self-interaction can be produced from thermal freeze-out in the presence of SM-annihilation, SIMP and/or forbidden channels. We show that dark photon and/or dark Higgs should be relatively light for unitarity and then assist the thermal freeze-out. We identify the constraints on the parameter space of dark matter self-interaction and mass in cases that one or some of the channels are important in determining the relic density.Comment: 26 pages, 11 figures, Version to appear in Journal of High Energy Physic

Unitary inflaton as decaying dark matter

We consider the inflation model of a singlet scalar field (sigma field) with both quadratic and linear non-minimal couplings where unitarity is ensured up to the Planck scale. We assume that a $Z_2$ symmetry for the sigma field is respected by the scalar potential in Jordan frame but it is broken explicitly by the linear non-minimal coupling due to quantum gravity. We discuss the impacts of the linear non-minimal coupling on various dynamics from inflation to low energy, such as a sizable tensor-to-scalar ratio, a novel reheating process with quartic potential dominance, and suppressed physical parameters in the low energy, etc. In particular, the linear non-minimal coupling leads to the linear couplings of the sigma field to the Standard Model through the trace of the energy-momentum tensor in Einstein frame. Thus, regarding the sigma field as a decaying dark matter, we consider the non-thermal production mechanisms for dark matter from the decays of Higgs and inflaton condensate and show the parameter space that is compatible with the correct relic density and cosmological constraints.Comment: 36 pages, 7 figures, v2: minor corrections made and references added, v3: discussion on preheating added, accepted for Journal of High Energy Physics, v4: Lyman-alpha bound included and inflationary predictions refined for perturbative reheatin

A minimal flavored U(1)′U(1)' for BB-meson anomalies

We consider an anomaly-free $U(1)'$ model with favorable couplings to heavy flavors in the Standard Model(SM), as motivated by $B$-meson anomalies at LHCb. Taking the $U(1)'$ charge to be $Q'=y(L_\mu-L_\tau)+ x(B_3-L_3)$, we can explain the $B$-meson anomalies without invoking extra charged fermions or flavor violation beyond the SM. We show that there is a viable parameter space with a small $x$ that is compatible with other meson decays, tau lepton and neutrino experiments as well as the LHC dimuon searches. We briefly discuss the prospects of discovering the $Z'$ gauge boson at the LHC in the proposed model.Comment: 20 pages, 4 figures, v2: references and discussion on electroweak precision test added, v3: Version to appear in Physical Review

Control Method Of Circulating Refrigerant Amount For Heat Pump System

A heat pump system requires proper refrigerant charge amount. Once refrigerant is charged into a heat pump system, its charge amount is fixed. For this reason, prediction of optimal refrigerant charge amount is very important in order to yield best performance. Too low charge amount degrades capacity of heat pump. On the other hand, excessive charge amount decreases coefficient of performance (COP). The optimal value of refrigerant charge amount highly depends on secondary fluid temperature conditions. Consequently, fixed charge amount of refrigerant in heat pump shows the best performance only at certain temperature condition. Several ideas have revealed to change charge amount of the heat pump system. One is to have an additional reservoir to store or release refrigerant which is attached to a heat pump system. This method may seem simple but to measure exact amount of refrigerant in reservoir, additional pressure transducer, temperature measurement device, level sensor and other apparatus are required that increase the cost of heat pump. Another idea is to have reservoir between condenser outlet and expansion device. Rajapaksha and Suen (2004) showed that existence of reservoir at this point helps improve capacity while reducing the system COP. In this study, a new method for refrigerant charge amount control technique is presented. It has very simple control logic and requires only a few additional cost factors; several valves and additional tubes are only required. This method is based on different refrigerant phase distribution at each point of inlet and outlet of components in heat pump system. In a simple cycle heat pump system, refrigerant at condenser outlet (before expansion device) is in a subcooled liquid state at high pressure, while refrigerant is in a superheated vapor state at evaporator outlet (before compressor inlet) at low pressure. This technique regulates refrigerant charge by holding some volume of refrigerant in the connecting tube of considerable volume installed between the condenser outlet and the evaporator outlet. Using several solenoid valves (on/off) desired amount of refrigerant can be stored into a volume provided by a connecting tube. This connected volume is referred as ‘stagnation volume’ (Vstag). When one of this installed valve is closed and the rest of the valves are open, certain amount of refrigerant is stored in the stagnation volume (Vstag) while operating heat pump system. If closed valve is adjacent to condenser outlet, charge amount to the heat pump system increases while the charge is reduced when the valve adjacent to evaporator outlet is closed. This method is numerically verified and there are very little variation of COP. Therefore, heat pump can be operated at optimized circulating amount of refrigerant in spite of the secondary fluid temperature variation during heating or cooling operation