1,379 research outputs found
The Ubiquitous Throat
We attempt to quantify the widely-held belief that large hierarchies induced
by strongly-warped geometries are common in the string theory landscape. To
this end, we focus on the arguably best-understood subset of vacua -- type IIB
Calabi-Yau orientifolds with non-perturbative Kaehler stabilization and a
SUSY-breaking uplift (the KKLT setup). Within this framework, vacua with a
realistically small cosmological constant are expected to come from Calabi-Yaus
with a large number of 3-cycles. For appropriate choices of flux numbers, many
of these 3-cycles can, in general, shrink to produce near-conifold geometries.
Thus, a simple statistical analysis in the spirit of Denef and Douglas allows
us to estimate the expected number and length of Klebanov-Strassler throats in
the given set of vacua. We find that throats capable of explaining the
electroweak hierarchy are expected to be present in a large fraction of the
landscape vacua while shorter throats are essentially unavoidable in a
statistical sense.Comment: References added, typos fixed. LaTex, 17 pages, 1 figur
The Small Observed Baryon Asymmetry from a Large Lepton Asymmetry
Primordial Big-Bang Nucleosynthesis (BBN) tightly constrains the existence of
any additional relativistic degrees of freedom at that epoch. However a large
asymmetry in electron neutrino number shifts the chemical equilibrium between
the neutron and proton at neutron freeze-out and allows such additional
particle species. Moreover, the BBN itself may also prefer such an asymmetry to
reconcile predicted element abundances and observations. However, such a large
asymmetry appears to be in conflict with the observed small baryon asymmetry if
they are in sphaleron mediated equilibrium. In this paper we point out the
surprising fact that in the Standard Model, if the asymmetries in the electron
number and the muon number are equal (and opposite) and of the size required to
reconcile BBN theory with observations, a baryon asymmetry of the Universe of
the correct magnitude and sign is automatically generated within a factor of
two. This small remaining discrepancy is naturally remedied in the
supersymmetric Standard Model.Comment: 14 page
A Unified Theory of Matter Genesis: Asymmetric Freeze-In
We propose a unified theory of dark matter (DM) genesis and baryogenesis. It
explains the observed link between the DM density and the baryon density, and
is fully testable by a combination of collider experiments and precision tests.
Our theory utilises the "thermal freeze-in" mechanism of DM production,
generating particle anti-particle asymmetries in decays from visible to hidden
sectors. Calculable, linked, asymmetries in baryon number and DM number are
produced by the feeble interaction mediating between the two sectors, while the
out-of-equilibrium condition necessary for baryogenesis is provided by the
different temperatures of the visible and hidden sectors. An illustrative model
is presented where the visible sector is the MSSM, with the relevant CP
violation arising from phases in the gaugino and Higgsino masses, and both
asymmetries are generated at temperatures of order 100 GeV. Experimental
signals of this mechanism can be spectacular, including: long-lived metastable
states late decaying at the LHC; apparent baryon-number or lepton-number
violating signatures associated with these highly displaced vertices; EDM
signals correlated with the observed decay lifetimes and within reach of
planned experiments; and a prediction for the mass of the dark matter particle
that is sensitive to the spectrum of the visible sector and the nature of the
electroweak phase transition.Comment: LaTeX, 22 pages, 6 figure
TeV scale resonant leptogenesis from supersymmetry breaking
We propose a model of TeV-scale resonant leptogenesis based upon recent
models of the generation of light neutrino masses from supersymmetry-breaking
effects with TeV-scale right-handed (rhd) neutrinos, . The model leads to
naturally large cosmological lepton asymmetries via the resonant behaviour of
the one-loop self-energy contribution to decay. Our model addresses the
primary problems of previous phenomenological studies of low-energy
leptogenesis: a rational for TeV-scale rhd neutrinos with small Yukawa
couplings so that the out-of equilibrium condition for decay is
satisfied; the origin of the tiny, but non-zero mass splitting required between
at least two masses; and the necessary non-trivial breaking of flavour
symmetries in the rhd neutrino sector. The low mass-scale of the rhd neutrinos
and their superpartners, and the TeV-scale -terms automatically contained
within the model offer opportunities for partial direct experimental tests of
this leptogenesis mechanism at future colliders.Comment: 10 Pages latex, version for JHE
Substructure Boosts to Dark Matter Annihilation from Sommerfeld Enhancement
The recently introduced Sommerfeld enhancement of the dark matter
annihilation cross section has important implications for the detection of dark
matter annihilation in subhalos in the Galactic halo. In addition to the boost
to the dark matter annihilation cross section from the high densities of these
subhalos with respect to the main halo, an additional boost caused by the
Sommerfeld enhancement results from the fact that they are kinematically colder
than the Galactic halo. If we further believe the generic prediction of CDM
that in each subhalo there is an abundance of substructure which is
approximately self-similar to that of the Galactic halo, then I show that
additional boosts coming from the density enhancements of these small
substructures and their small velocity dispersions enhance the dark matter
annihilation cross section even further. I find that very large boost factors
( to ) are obtained in a large class of models. The implications of
these boost factors for the detection of dark matter annihilation from dwarf
Spheroidal galaxies in the Galactic halo are such that, generically, they
outshine the background gamma-ray flux and are detectable by the Fermi
Gamma-ray Space Telescope.Comment: PRD in pres
Confining Flux Tubes in a Current Algebra Approach
We describe flux tubes and their interactions in a low energy sigma model
induced by flavor symmetry breaking in
QCD. Unlike standard QCD, this model allows gauge confinement to
manifest itself in the low energy theory, which has unscreened spinor color
sources and global flux tubes. We construct the flux tubes and show how
they mediate the confinement of spinor sources. We further examine the flux
tubes' quantum stability, spectrum and interactions. We find that flux tubes
are Alice strings, despite ambiguities in defining parallel transport.
Furthermore, twisted loops of flux tube support skyrmion number, just as gauged
Alice strings form loops that support monopole charge. This model, while
phenomenologically nonviable, thus affords a perspective on both the dynamics
of confinement and on subtleties which arise for global Alice strings.Comment: 29 pages (REVTEX) plus 6 figures, two corrections in the final
section and added reference
Phase transitions near black hole horizons
The Reissner-Nordstrom black hole in four dimensions can be made unstable
without violating the dominant energy condition by introducing a real massive
scalar with non-renormalizable interactions with the gauge field. New stable
black hole solutions then exist with greater entropy for fixed mass and charge
than the Reissner-Nordstrom solution. In these new solutions, the scalar
condenses to a non-zero value near the horizon. Various generalizations of
these hairy black holes are discussed, and an attempt is made to characterize
when black hole hair can occur.Comment: 30 pages, 6 figures. v2: minor corrections, references adde
Higgs bosons near 125 GeV in the NMSSM with constraints at the GUT scale
We study the NMSSM with universal Susy breaking terms (besides the Higgs
sector) at the GUT scale. Within this constrained parameter space, it is not
difficult to find a Higgs boson with a mass of about 125 GeV and an enhanced
cross section in the diphoton channel. An additional lighter Higgs boson with
reduced couplings and a mass <123 GeV is potentially observable at the LHC. The
NMSSM-specific Yukawa couplings lambda and kappa are relatively large and
tan(beta) is small, such that lambda, kappa and the top Yukawa coupling are of
order 1 at the GUT scale. The lightest stop can be as light as 105 GeV, and the
fine-tuning is modest. WMAP constraints can be satisfied by a dominantly
higgsino-like LSP with substantial bino, wino and singlino admixtures and a
mass of ~60-90 GeV, which would potentially be detectable by XENON100.Comment: 20 pages, 14 figure
The order of the phase transition in 3d U(1)+Higgs theory
We study the order of the phase transition in the 3d U(1)+Higgs theory, which
is the Ginzburg-Landau theory of superconductivity. We confirm that for small
scalar self-coupling the transition is of first order. For large scalar
self-coupling the transition ceases to be of first order, and a non-vanishing
scalar mass suggests that the transition may even be of higher than second
order.Comment: Poster at LATTICE96(electroweak). 4 pages, 5 figure
A remark on sphaleron erasure of baryon asymmetry
We complete an existing result for how the baryon asymmetry left over after a
period of full thermal equilibrium depends on different lepton asymmetries.Comment: 5 pages; small clarifications and a reference added; to appear in PR
- …