16 research outputs found
The (ir)Relevance of Initial Conditions in Soft Leptogenesis
We explore how the initial conditions affect the final lepton asymmetry in
Soft Leptogenesis. It has been usually assumed that the initial state is a
statistical mixture of sterile sneutrinos and anti-sneutrinos with equal
abundances. We calculate the lepton asymmetry due to the most general initial
mixture. The usually assumed equal mixture produces a small, but sufficient,
lepton asymmetry which is proportional to the ratio of the supersymmetry
breaking scale over the Majorana scale. A more generic mixture, still with
equal contents of sneutrinos and anti sneutrinos, yields an unsuppressed lepton
asymmetry. Mixtures of non equal contents of sneutrinos and anti sneutrinos
result in a large lepton asymmetry too. While these results establish the
robustness of Soft Leptogenesis and other mixing based mechanisms, they also
expose their lack of predictive power.Comment: v1: 12 pages; v2: typos corrected; v3: published version with new
discussions and reference
Direct Detection with Dark Mediators
We introduce dark mediator Dark matter (dmDM) where the dark and visible
sectors are connected by at least one light mediator carrying the same
dark charge that stabilizes DM. is coupled to the Standard Model via an
operator , and to dark matter via a Yukawa
coupling . Direct detection is realized as
the process at tree-level
for and small Yukawa coupling, or
alternatively as a loop-induced process . We explore the direct-detection consequences of this scenario and find
that a heavy dmDM candidate fakes different
standard WIMPs in different experiments. Large
portions of the dmDM parameter space are detectable above the irreducible
neutrino background and not yet excluded by any bounds. Interestingly, for the
range leading to novel direct detection phenomenology, dmDM is also a
form of Self-Interacting Dark Matter (SIDM), which resolves inconsistencies
between dwarf galaxy observations and numerical simulations.Comment: 9 pages, 8 figures + reference
WIMPless Dark Matter in Anomaly-Mediated Supersymmetry Breaking with Hidden QED
In anomaly-mediated supersymmetry breaking, superpartners in a hidden sector
have masses that are proportional to couplings squared, and so naturally freeze
out with the desired dark matter relic density for a large range of masses. We
present an extremely simple realization of this possibility, with WIMPless dark
matter arising from a hidden sector that is supersymmetric QED with N_F
flavors. Dark matter is multi-component, composed of hidden leptons and
sleptons with masses anywhere from 10 GeV to 10 TeV, and hidden photons provide
the thermal bath. The dark matter self-interacts through hidden sector Coulomb
scatterings that are potentially observable. In addition, the hidden photon
contribution to the number of relativistic degrees of freedom is in the range
\Delta N_eff ~ 0 - 2, and, if the hidden and visible sectors were initially in
thermal contact, the model predicts \Delta N_eff ~ 0.2 - 0.4. Data already
taken by Planck may provide evidence of such deviations.Comment: 17 page
WIMPless Dark Matter from an AMSB Hidden Sector with No New Mass Parameters
We present a model with dark matter in an anomaly-mediated supersymmetry
breaking hidden sector with a U(1)xU(1) gauge symmetry. The symmetries of the
model stabilize the dark matter and forbid the introduction of new mass
parameters. As a result, the thermal relic density is completely determined by
the gravitino mass and dimensionless couplings. Assuming non-hierarchical
couplings, the thermal relic density is ~ 0.1, independent of the dark matter's
mass and interaction strength, realizing the WIMPless miracle. The model has
several striking features. For particle physics, stability of the dark matter
is completely consistent with R-parity violation in the visible sector, with
implications for superpartner collider signatures; also the thermal relic's
mass may be ~ 10 GeV or lighter, which is of interest given recent direct
detection results. Interesting astrophysical signatures are dark matter
self-interactions through a long-range force, and massless hidden photons and
fermions that contribute to the number of relativistic degrees of freedom at
BBN and CMB. The latter are particularly interesting, given current indications
for extra degrees of freedom and near future results from the Planck
observatory.Comment: 18 pages, pdflate
Confluence of Constraints in Gauge Mediation: The 125 GeV Higgs Boson and Goldilocks Cosmology
Recent indications of a 125 GeV Higgs boson are challenging for
gauge-mediated supersymmetry breaking (GMSB), since radiative contributions to
the Higgs boson mass are not enhanced by significant stop mixing. This
challenge should not be considered in isolation, however, as GMSB also
generically suffers from two other problems: unsuppressed electric dipole
moments and the absence of an attractive dark matter candidate. We show that
all of these problems may be simultaneously solved by considering heavy
superpartners, without extra fields or modified cosmology. Multi-TeV sfermions
suppress the EDMs and raise the Higgs mass, and the dark matter problem is
solved by Goldilocks cosmology, in which TeV neutralinos decay to GeV
gravitinos that are simultaneously light enough to solve the flavor problem and
heavy enough to be all of dark matter. The implications for collider searches
and direct and indirect dark matter detection are sobering, but EDMs are
expected near their current bounds, and the resulting non-thermal gravitino
dark matter is necessarily warm, with testable cosmological implications.Comment: pdflatex, 15 pages, 11 figure