Hyperon-rich matter and kaons in matter

We discuss the equation of state of neutron stars in the dense interior considering hyperons and the possible onset of kaon condensation within the relativistic mean field model. We find that hyperons are favoured in dense matter and that their appearance makes the existence of a kaon condensed phase quite unlikely. Implications for the recent measurements of kaons in heavy ion collisions at subthreshold energy are also given.     

Quark matter nucleation in hot hadronic matter

We study the quark deconfinement phase transition in hot β-stable hadronic matter. Assuming a first order phase transition, we calculate the enthalpy per baryon of the hadron–quark phase transition. We calculate and compare the nucleation rate and the nucleation time due to thermal and quantum nucleation mechanisms. We compute the crossover temperature above which thermal nucleation dominates the finite temperature quantum nucleation mechanism. We next discuss the consequences for the physics of proto-neutron stars. We introduce the concept of limiting conversion temperature and critical mass M_cr for proto-hadronic stars, and we show that proto-hadronic stars with a mass M<M_cr could survive the early stages of their evolution without decaying to a quark star.     

Artificial graphenes: Dirac matter beyond condensed matter

After the discovery of graphene and of its many fascinating properties, there has been a growing interest for the study of “artificial graphenes”. These are totally different and novel systems that bear exciting similarities with graphene. Among them are lattices of ultracold atoms, microwave or photonic lattices, “molecular graphene” or new compounds like phosphorene. The advantage of these structures is that they serve as new playgrounds for measuring and testing physical phenomena that may not be reachable in graphene, in particular the possibility of controlling the existence of Dirac points (or Dirac cones) existing in the electronic spectrum of graphene, of performing interference experiments in reciprocal space, of probing geometrical properties of the wave functions, of manipulating edge states, etc. These cones, which describe the band structure in the vicinity of the two connected energy bands, are characterized by a topological “charge”. They can be moved in the reciprocal space by appropriate modification of external parameters (pressure, twist, sliding, stress, etc.). They can be manipulated, created or suppressed under the condition that the total topological charge be conserved. In this short review, I discuss several aspects of the scenarios of merging or emergence of Dirac points as well as the experimental investigations of these scenarios in condensed matter and beyond.     

Superdense matter

We review recent work on the phase structure of QCD at very high baryon density. We introduce the phenomenon of color superconductivity and discuss the use of weak coupling methods. We study the phase structure as a function of the number of flavors and their masses. We also introduce effective theories that describe low energy excitations at high baryon density. Finally, we comment on the possibility of kaon condensation at very large baryon density.     

Lepto-quark matter

In certain extensions of the standard model with additionalU(1) gauge symmetries, the anomalies between the quarks and leptons no longer cancel. It is shown that the anomalies can be cancelled by invoking representations oflepto-quark fermions. Lepto-quarks represent new fermionic matter that carries quark as well as lepton numbers. An extension of the standard model with three and four families of conventional quarks and leptons is presented in which freedom from anomalies is secured through the presence of lepto-quark matter representations. The gauge symmetry of the model isSU(2) _L XU(1) _q XU(1) _l whereU(1) _q andU(1) _l refer to distinct hypercharge sources for the quarks and the leptons.     

Dark matter, neutron stars, and strange quark matter

We show that self-annihilating weakly interacting massive particle (WIMP) dark matter accreted onto neutron stars may provide a mechanism to seed compact objects with long-lived lumps of strange quark matter, or strangelets, for WIMP masses above a few GeV. This effect may trigger a conversion of most of the star into a strange star. We use an energy estimate for the long-lived strangelet based on the Fermi-gas model combined with the MIT bag model to set a new limit on the possible values of the WIMP mass that can be especially relevant for subdominant species of massive neutralinos.     

Unified origin for baryonic visible matter and antibaryonic dark matter

We present a novel mechanism for generating both the baryon and dark matter densities of the Universe. A new Dirac fermion X carrying a conserved baryon number charge couples to the standard model quarks as well as a GeV-scale hidden sector. CP-violating decays of X, produced nonthermally in low-temperature reheating, sequester antibaryon number in the hidden sector, thereby leaving a baryon excess in the visible sector. The antibaryonic hidden states are stable dark matter. A spectacular signature of this mechanism is the baryon-destroying inelastic scattering of dark matter that can annihilate baryons at appreciable rates relevant for nucleon decay searches.     

暗物质的理论研究进展

文章简要综述了以下内容:(1)晴物质存在的证据,以及它为什么很可能与目前粒子物理研究紧密相关;(2)晴物质的性质,并以超对称模型和额外维模型为例,讨论了包含暗物质粒子的模型;(3)最近Pamela/Atic/Fermi实验观测对于暗物质性质的新认识;(4)讨论和展望.     

Brane-world dark matter

We show that, in the context of brane-world scenarios with low tension tau=f(4), massive brane fluctuations (branons) are natural dark matter candidates. We calculate the present abundances for both hot (warm) and cold branons in terms of the branon mass M and the tension scale f. The results are compared with the current experimental bounds on these parameters. We also study the prospects for their detection in direct search experiments and comment on their characteristic signals in the indirect ones.     

Nuclear matter distributions

The present knowledge of the distribution of neutrons and protons in the nucleus is reviewed. The distributions calculated by the single-particle potential method and from the Hartree-Fock theory are compared with the experimental data. Particular attention is paid to the hyperfine anomaly and the isotope shifts, and to the connection with the distribution of nuclear magnetisation.     

Non-baryonic dark matter

The need for dark matter is briefly reviewed. A wealth of observational information points to the existence of a non-baryonic component. To the theoretically favoured candidates today belong axions, supersymmetric particles, and to some extent massive neutrinos. The theoretical foundation and experimental situation for each of these is reviewed. In particular, indirect detection methods of supersymmetric dark matter are described. Present experiments are just reaching the required sensitivity to discover or rule out some of these candidates, and major improvements are planned over the next few years.     

Number-theory dark matter

We propose that the stability of dark matter is ensured by a discrete subgroup of the U(1)_B–L gauge symmetry, Z₂(B–L)$Z_2(\mathrm{B}\text{–}\mathrm{L})$. We introduce a set of chiral fermions charged under the U(1)_B–L in addition to the right-handed neutrinos, and require the anomaly-cancellation conditions associated with the U(1)_B–L gauge symmetry. We find that the possible number of fermions and their charges are tightly constrained, and that non-trivial solutions appear when at least five additional chiral fermions are introduced. The Fermat theorem in the number theory plays an important role in this argument. Focusing on one of the solutions, we show that there is indeed a good candidate for dark matter, whose stability is guaranteed by Z₂(B–L)$Z_2(\mathrm{B}\text{–}\mathrm{L})$.     

Isospin-violating dark matter

Searches for dark matter scattering off nuclei are typically compared assuming that the dark matter?s spin-independent couplings are identical for protons and neutrons. This assumption is neither innocuous nor well motivated. We consider isospin-violating dark matter (IVDM) with one extra parameter, the ratio of neutron to proton couplings, and include the isotope distribution for each detector. For a single choice of the coupling ratio, the DAMA and CoGeNT signals are consistent with each other and with current XENON constraints, and they unambiguously predict near future signals at XENON and CRESST. We provide a quark-level realization of IVDM as WIMPless dark matter that is consistent with all collider and low-energy bounds.