88 research outputs found
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 , where
and 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 .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 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
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 -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 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
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