49 research outputs found
Probing Gravitational Interactions of Elementary Particles
The gravitational interactions of elementary particles are suppressed by the
Planck scale M_P ~ 10^18 GeV and are typically expected to be far too weak to
be probed by experiments. We show that, contrary to conventional wisdom, such
interactions may be studied by particle physics experiments in the next few
years. As an example, we consider conventional supergravity with a stable
gravitino as the lightest supersymmetric particle. The next-lightest
supersymmetric particle (NLSP) decays to the gravitino through gravitational
interactions after about a year. This lifetime can be measured by stopping
NLSPs at colliders and observing their decays. Such studies will yield a
measurement of Newton's gravitational constant on unprecedentedly small scales,
shed light on dark matter, and provide a window on the early universe.Comment: 6 pages, second prize in the 2004 Gravity Research Foundation essay
competitio
Superweakly Interacting Massive Particles
We investigate a new class of dark matter: superweakly-interacting massive
particles (superWIMPs). As with conventional WIMPs, superWIMPs appear in
well-motivated particle theories with naturally the correct relic density. In
contrast to WIMPs, however, superWIMPs are impossible to detect in all
conventional dark matter searches. We consider the concrete examples of
gravitino and graviton cold dark matter in models with supersymmetry and
universal extra dimensions, respectively, and show that superWIMP dark matter
satisfies stringent constraints from Big Bang nucleosynthesis and the cosmic
microwave background.Comment: 4 pages, 4 figures, published versio
Goldilocks Supersymmetry: Simultaneous Solution to the Dark Matter and Flavor Problems of Supersymmetry
Neutralino dark matter is well motivated, but also suffers from two
shortcomings: it requires gravity-mediated supersymmetry breaking, which
generically violates flavor constraints, and its thermal relic density \Omega
is typically too large. We propose a simple solution to both problems:
neutralinos freezeout with \Omega ~10-100, but then decay to ~1 GeV gravitinos,
which are simultaneously light enough to satisfy flavor constraints and heavy
enough to be all of dark matter. This scenario is naturally realized in
high-scale gauge-mediation models, ameliorates small scale structure problems,
and implies that ``cosmologically excluded'' models may, in fact, be
cosmologically preferred.Comment: 4 pages; v2: references added; v3: published versio
Study of lepton flavor violation in flavor symmetric models for lepton sector
Flavor symmetric model is one of the attractive Beyond Standard Models (BSMs)
to reveal the flavor structure of the Standard Model (SM). A lot of efforts
have been put into the model building and we find many kinds of flavor
symmetries and setups are able to explain the observed fermion mass matrices.
In this paper, we look for common predictions of physical observables among the
ones in flavor symmetric models, and try to understand how to test flavor
symmetry in experiments. Especially, we focus on the BSMs for leptons with
extra Higgs doublets charged under flavor symmetry. In many flavor
models for leptons, remnant symmetry is partially respected after the flavor
symmetry breaking, and it controls well the Flavor Changing Neutral Currents
(FCNCs) and suggests some crucial predictions against the flavor changing
process, although the remnant symmetry is not respected in the full lagrangian.
In fact, we see that and processes are the most important in the
flavor models that the extra Higgs doublets belong to triplet representation of
flavor symmetry. For instance, the stringent constraint from the process could be evaded according to the partial remnant symmetry. We
also investigate the breaking effect of the remnant symmetry mediated by the
Higgs scalars, and investigate the constraints from the flavor physics: the
flavor violating and decays, the electric dipole moments, and the
muon anomalous magnetic moment. We also discuss the correlation between FCNCs
and nonzero , and point out the physical observables in the
charged lepton sector to test the BSMs for the neutrino mixing.Comment: 29 pages, 11 figure
SuperWIMP Gravitino Dark Matter from Slepton and Sneutrino Decays
Dark matter may be composed of superWIMPs, superweakly-interacting massive
particles produced in the late decays of other particles. We focus on the case
of gravitinos produced in the late decays of sleptons or sneutrinos and assume
they are produced in sufficient numbers to constitute all of non-baryonic dark
matter. At leading order, these late decays are two-body and the accompanying
energy is electromagnetic. For natural weak-scale parameters, these decays have
been shown to satisfy bounds from Big Bang nucleosynthesis and the cosmic
microwave background. However, sleptons and sneutrinos may also decay to
three-body final states, producing hadronic energy, which is subject to even
more stringent nucleosynthesis bounds. We determine the three-body branching
fractions and the resulting hadronic energy release. We find that superWIMP
gravitino dark matter is viable and determine the gravitino and
slepton/sneutrino masses preferred by this solution to the dark matter problem.
In passing, we note that hadronic constraints disfavor the possibility of
superWIMPs produced by neutralino decays unless the neutralino is photino-like.Comment: 22 pages, updated figures and minor changes, version to appear in
Phys. Rev.