This paper describes the physics case for a new fixed target facility at CERN SPS. The SHiP (search for hidden particles) experiment is intended to hunt for new physics in the largely unexplored domain of very weakly interacting particles with masses below the Fermi scale, inaccessible to the LHC experiments, and to study tau neutrino physics. The same proton beam setup can be used later to look for decays of tau-leptons with lepton flavour number non-conservation, [Formula: see text] and to search for weakly-interacting sub-GeV dark matter candidates. We discuss the evidence for physics beyond the standard model and describe interactions between new particles and four different portals-scalars, vectors, fermions or axion-like particles. We discuss motivations for different models, manifesting themselves via these interactions, and how they can be probed with the SHiP experiment and present several case studies. The prospects to search for relatively light SUSY and composite particles at SHiP are also discussed. We demonstrate that the SHiP experiment has a unique potential to discover new physics and can directly probe a number of solutions of beyond the standard model puzzles, such as neutrino masses, baryon asymmetry of the Universe, dark matter, and inflation.

In the present paper the gauge-invariant formalism is developed for perturbations of the braneworld model in which our universe is realized as a boundary of a higher-dimensional spacetime. For the background model in which the bulk spacetime is (n + m)-dimensional and has the spatial symmetry corresponding to the isometry group of a n-dimensional maximally symmetric space, gauge-invariant equations are derived for perturbations of the bulk spacetime. Further, for the case corresponding to the brane-world model in which m = 2 and the brane is a boundary invariant under the spatial symmetry in the unperturbed background, relations between the gauge-invariant variables describing the bulk perturbations and those for brane perturbations are derived from Israel's junction condition under the assumption of Z2 symmetry. In particular, for the case in which the bulk spacetime is a constant-curvature spacetime, it is shown that the bulk perturbation equations reduce to a single hyperbolic master equation for a master variable, and that the physical condition on the gauge-invariant variable describing the intrinsic stress perturbation of the brane yields a boundary condition for the master equation through the junction condition. On the basis of this formalism, it is pointed out that it seems to be difficult to suppress brane perturbations corresponding to massive excitations for a brane motion giving a realistic expanding universe model.

We propose an extended version of the standard model, in which neutrino oscillation, dark matter, and baryon asymmetry of the Universe can be simultaneously explained by the TeV-scale physics without assuming large hierarchy among the mass scales. Tiny neutrino masses are generated at the three loop level due to the exact Z2 symmetry, by which stability of the dark matter candidate is guaranteed. The extra Higgs doublet is required not only for the tiny neutrino masses but also for successful electroweak baryogenesis. The model provides discriminative predictions especially in Higgs phenomenology, so that it is testable at current and future collider experiments.PACS numbers: 14.60. Pq, 14.60.St, 14.80.Cp, 12.60.Fr [January 7, 2009] Although the standard model (SM) for elementary particles has been successful for over three decades, the Higgs sector remains unknown. The discovery of a Higgs boson is the most important issue at the CERN Large Hadron Collider (LHC). On the other hand, today we have definite reasons to consider a model beyond the SM. First of all, the data indicate that neutrinos have tiny masses and mix with each other [1]. Second, cosmological observations have revealed that the energy density of dark matter (DM) in the Universe dominates that of baryonic matter [2]. Finally, asymmetry of matter and anti-matter in our Universe has been addressed as a serious problem regarding existence of ourselves [3]. They are all beyond the scope of the SM, so that an extension of the SM is required to explain these phenomena, which would be related to the physics of electroweak symmetry breaking.A simple scenario to generate tiny masses (m ν ) for left-handed (LH) neutrinos would be based on the seesaw mechanism with heavy right-handed (RH) neutrinos [4];13−16 GeV) is the Majorana mass of RH neutrinos, and m D is the Dirac mass of the electroweak scale. This scenario would be compatible with the framework with large mass scales like grand unification. However, introduction of such large scales causes a problem of hierarchy. In addition, the decoupling theorem[5] makes it far from experimental tests.In this letter, we propose an alternative model which would explain neutrino oscillation, origin of DM and baryon asymmetry simultaneously by an extended Higgs sector with RH neutrinos. In order to avoid large hierarchy, masses of the RH neutrinos are to be at most TeV scales. Tiny neutrino masses are then generated at the three loop level due to an exact discrete symmetry, by which tree-level Yukawa couplings of neutrinos are prohibited. The lightest neutral odd state under the discrete symmetry is a candidate of DM. Baryon asymmetry can be generated at the electroweak phase transition (EWPT) by additional CP violating phases in the Higgs sector [6,7]. In this framework, a successful model can be built without contradiction of the current data.Original idea of generating tiny neutrino masses via the radiative effect has been proposed by Zee[8]. The extension with a TeV-scale RH neutrino has been discussed in R...

Entropy production by the dilaton decay is studied in the model where the dilaton acquires potential via gaugino condensation in the hidden gauge group. Its effect on the Affleck-Dine baryogenesis is investigated with and without non-renormalizable terms in the potential. It is shown that the baryon asymmetry produced by this mechanism with the higher-dimensional terms is diluted by the dilaton decay and can be regulated to the observed value.

We consider cosmological consequences of a heavy axino, decaying to the neutralino in R-parity conserving models. The importance and influence of the axino decay on the resultant abundance of neutralino dark matter depends on the lifetime and the energy density of axino. For a high reheating temperature after inflation, copiously produced axinos dominate the energy density of the universe and its decay produces a large amount of entropy. As a bonus, we obtain that the upper bound on the reheating temperature after inflation via gravitino decay can be moderated, because the entropy production by the axino decay more or less dilutes the gravitinos. I. AXINONeutralino, if it is the lightest supersymmetric particle (LSP) in R-parity conserving models, is a natural candidate for dark matter. Because of the TeV scale sparticle interactions, the thermal history of neutralinos allows the neutralino dark matter possibility. But, imposing a solution of the strong CP problem, the thermal history involves contributions from the additional sector.The strong CP problem is naturally solved by introducing a very light axion a. Most probably, it appears when the Peccei-Quinn (PQ) symmetry is broken at a scale of f a . Below the PQ scale, the effective axion interaction with gluons iswhere g s is the strong coupling constant [1]. The PQ scale is constrained by the astrophysical and cosmological considerations in the narrow window 10 10 GeV f a 10 12 GeV [2].TeV scale supersymmetry (SUSY) suggests axinoã, the superpartner of axion, around the electroweak scale in the gravity mediation scenario. Here, we consider the effects of heavy axinos in cosmology. The axino cosmology depends crucially on the axino decoupling temperature [3], The axion supermultiplet includes axion, saxion (the scalar partner) and axino. Both saxion and axino masses are split from the almost vanishing axion mass if SUSY is broken. The precise value of the axino mass depends on the model, specified by the SUSY breaking sector and the mediation sector to the axion supermultiplet [4]. In principle, the axion supermultiplet is independent from the observable sector in which case we may take the axino mass as a free parameter of order from keV to a value much larger than the gravitino mass [5,6]. Light axinos can be a dark matter (DM) candidate, which has been studied extensively [7,8,9]. Heavy axinos, however, cannot be the LSP and can decay to the LSP plus light particles. This heavy axino decay to neutralino was considered in the literature [6] where the neutralino relic density was not considered seriously. Some considered the axino as the next LSP decaying to the gravitino LSP in the gauge mediated SUSY breaking scenario [10]. Recently, supersymmetric axion models were studied with an emphasis on saxion [11], where the heavy axino possibility was also considered briefly [12].In this paper, we present a more or less complete cosmological analysis of a heavy axino with mass in the TeV region so that it is heavier than the LSP neutralino. Compared with the saxi...