Nonlinear superhorizon perturbations of non-canonical scalar field

We develop a theory of non-linear cosmological perturbations at superhorizon scales for a scalar field with a Lagrangian of the form $P(X,\phi)$, where $X=-\partial^{\mu}\phi\partial_{\mu}\phi$ and $\phi$ is the scalar field. We employ the ADM formalism and the spatial gradient expansion approach to obtain general solutions valid up to the second order in the gradient expansion. This formulation can be applied to, for example, DBI inflation models to investigate superhorizon evolution of non-Gaussianities. With slight modification, we also obtain general solutions valid up to the same order for a perfect fluid with a general equation of state $P=P(\rho)$.Comment: 14 page

Pseudomoduli Dark Matter

We point out that pseudomoduli -- tree-level flat directions that often accompany dynamical supersymmetry breaking -- can be natural candidates for TeV-scale dark matter in models of gauge mediation. The idea is general and can be applied to different dark matter scenarios, including (but not limited to) those of potential relevance to recent cosmic ray anomalies. We describe the requirements for a viable model of pseudomoduli dark matter, and we analyze two example models to illustrate the general mechanism -- one where the pseudomoduli carry Higgsino-like quantum numbers, and another where they are SM singlets but are charged under a hidden-sector $U(1)'$ gauge group.Comment: 20 pages, refs adde

Schwarzschild Solution on the Brane

In this communication we have shown that Schwarzschild solution is possible in brane world for some specific choices of brane matter and the non local effects from the bulk. A conformally flat bulk space time with fine-tuned vacuum energy (brane tension) shows that, Schwarzschild solution may also be the vacuum solution for brane world scenario.Comment: 3 page

Selectron Studies at e-e- and e+e- Colliders

Selectrons may be studied in both e-e- and e+e- collisions at future linear colliders. Relative to e+e-, the e-e- mode benefits from negligible backgrounds and \beta threshold behavior for identical selectron pair production, but suffers from luminosity degradation and increased initial state radiation and beamstrahlung. We include all of these effects and compare the potential for selectron mass measurements in the two modes. The virtues of the e-e- collider far outweigh its disadvantages. In particular, the selectron mass may be measured to 100 MeV with a total integrated luminosity of 1 fb^-1, while more than 100 fb^-1 is required in e+e- collisions for similar precision.Comment: 16 pages, 11 figure

Natural Little Hierarchy from a Partially Goldstone Twin Higgs

We construct a simple theory in which the fine-tuning of the standard model is significantly reduced. Radiative corrections to the quadratic part of the scalar potential are constrained to be symmetric under a global U(4) x U(4)' symmetry due to a discrete Z_2 "twin" parity, while the quartic part does not possess this symmetry. As a consequence, when the global symmetry is broken the Higgs fields emerge as light pseudo-Goldstone bosons, but with sizable quartic self-interactions. This structure allows the cutoff scale, \Lambda, to be raised to the multi-TeV region without significant fine-tuning. In the minimal version of the theory, the amount of fine-tuning is about 15% for \Lambda = 5 TeV, while it is about 30% in an extended model. This provides a solution to the little hierarchy problem. In the minimal model, the "visible" particle content is exactly that of the two Higgs doublet standard model, while the extended model also contains extra vector-like fermions with masses ~(1-2)TeV. At the LHC, our minimal model may appear exactly as the two Higgs doublet standard model, and new physics responsible for cutting off the divergences of the Higgs mass-squared parameter may not be discovered. Several possible processes that may be used to discriminate our model from the simple two Higgs doublet model are discussed for the LHC and for a linear collider.Comment: 22 page

Bulk fields with general brane kinetic terms

We analyse the effect of general brane kinetic terms for bulk scalars, fermions and gauge bosons in theories with extra dimensions, with and without supersymmetry. We find in particular a singular behaviour when these terms contain derivatives orthogonal to the brane. This is brought about by $\delta(0)$ divergences arising at second and higher order in perturbation theory. We argue that this behaviour can be smoothed down by classical renormalization.Comment: 31 pages, v2 few typos correcte

Multi-dimensional classical and quantum cosmology: Exact solutions, signature transition and stabilization

We study the classical and quantum cosmology of a $(4+d)$-dimensional spacetime minimally coupled to a scalar field and present exact solutions for the resulting field equations for the case where the universe is spatially flat. These solutions exhibit signature transition from a Euclidean to a Lorentzian domain and lead to stabilization of the internal space, in contrast to the solutions which do not undergo signature transition. The corresponding quantum cosmology is described by the Wheeler-DeWitt equation which has exact solutions in the mini-superspace, resulting in wavefunctions peaking around the classical paths. Such solutions admit parametrizations corresponding to metric solutions of the field equations that admit signature transition.Comment: 15 pages, two figures, to appear in JHE

Light Unstable Sterile Neutrino

The three massless active (doublet) neutrinos may mix with two heavy and one \underline {light} sterile (singlet) neutrinos so that the induced masses and mixings among the former are able to explain the present data on atmospheric and solar neutrino oscillations. If the LSND result is also to be explained, one active neutrino mass eigenstate must mix with the light sterile neutrino. A specific model is proposed with the spontaneous and soft explicit breaking of a new global $U(1)_S$ symmetry so that a sterile neutrino will decay into an active antineutrino and a nearly massless pseudo-Majoron.Comment: Discussion and references adde

Modelling non-dust fluids in cosmology

Currently, most of the numerical simulations of structure formation use Newtonian gravity. When modelling pressureless dark matter, or `dust', this approach gives the correct results for scales much smaller than the cosmological horizon, but for scenarios in which the fluid has pressure this is no longer the case. In this article, we present the correspondence of perturbations in Newtonian and cosmological perturbation theory, showing exact mathematical equivalence for pressureless matter, and giving the relativistic corrections for matter with pressure. As an example, we study the case of scalar field dark matter which features non-zero pressure perturbations. We discuss some problems which may arise when evolving the perturbations in this model with Newtonian numerical simulations and with CMB Boltzmann codes.Comment: 5 pages; v2: typos corrected and refs added, submitted version; v3: version to appear in JCA

N=1* in 5 dimensions: Dijkgraaf-Vafa meets Polchinski-Strassler

One of the powerful techniques to analyze the 5 dimensional Super Yang Mills theory with a massive hypermultiplet (N=1*) is provided by the AdS/CFT correspondence. It predicts that, for certain special values of the hypermultiplet mass, this theory develops nonperturbative branches of the moduli space as well as new light degrees of freedom. We use the higher dimensional generalization of the matrix model/gauge theory correspondence and recover all the prediction of the supergravity analysis. We construct the map between the four dimensional holomorphic superpotential and the five dimensional action and explicitly show that the superpotential is flat along the nonperturbative branches. This is the first instance in which the Dijkgraaf-Vafa method is used to analyze intrinsically higher dimensional phenomena.Comment: 28 pages, Late