1,030 research outputs found
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
Halo Shape and Relic Density Exclusions of Sommerfeld-Enhanced Dark Matter Explanations of Cosmic Ray Excesses
Dark matter with Sommerfeld-enhanced annihilation has been proposed to
explain observed cosmic ray positron excesses in the 10 GeV to TeV energy
range. We show that the required enhancement implies thermal relic densities
that are too small to be all of dark matter. We also show that the dark matter
is sufficiently self-interacting that observations of elliptical galactic dark
matter halos exclude large Sommerfeld enhancement for light force carriers.
Resonant Sommerfeld enhancement does not modify these conclusions, and the
astrophysical boosts required to resolve these discrepancies are disfavored,
especially when significant self-interactions suppress halo substructure.Comment: 4 pages, discussion and references added, published versio
Hidden Charged Dark Matter
Can dark matter be stabilized by charge conservation, just as the electron is
in the standard model? We examine the possibility that dark matter is hidden,
that is, neutral under all standard model gauge interactions, but charged under
an exact U(1) gauge symmetry of the hidden sector. Such candidates are
predicted in WIMPless models, supersymmetric models in which hidden dark matter
has the desired thermal relic density for a wide range of masses. Hidden
charged dark matter has many novel properties not shared by neutral dark
matter: (1) bound state formation and Sommerfeld-enhanced annihilation after
chemical freeze out may reduce its relic density, (2) similar effects greatly
enhance dark matter annihilation in protohalos at redshifts of z ~ 30, (3)
Compton scattering off hidden photons delays kinetic decoupling, suppressing
small scale structure, and (4) Rutherford scattering makes such dark matter
self-interacting and collisional, potentially impacting properties of the
Bullet Cluster and the observed morphology of galactic halos. We analyze all of
these effects in a WIMPless model in which the hidden sector is a simplified
version of the minimal supersymmetric standard model and the dark matter is a
hidden sector stau. We find that charged hidden dark matter is viable and
consistent with the correct relic density for reasonable model parameters and
dark matter masses in the range 1 GeV < m_X < 10 TeV. At the same time, in the
preferred range of parameters, this model predicts cores in the dark matter
halos of small galaxies and other halo properties that may be within the reach
of future observations. These models therefore provide a viable and
well-motivated framework for collisional dark matter with Sommerfeld
enhancement, with novel implications for astrophysics and dark matter searches.Comment: 29 pages; v2: references added; v3: published versio
Checkerboard charge density wave and pseudogap in high- cuprates
We consider the scenario where a 4-lattice constant, rotationally symmetric
charge density wave (CDW) is present in the underdoped cuprates. We prove a
theorem that puts strong constraint on the possible form factor of such a CDW.
We demonstrate, within mean-field theory, that a particular form factor within
the allowed class describes the angle-resolved photoemission and scan tunneling
spectroscopy well. We conjecture that the ``large pseudogap'' in cuprates is
the consequence of this type of charge density wave.Comment: We add a new section II on the symmetry property of the checkerboard
CD
Sommerfeld Enhancements for Thermal Relic Dark Matter
The annihilation cross section of thermal relic dark matter determines both
its relic density and indirect detection signals. We determine how large
indirect signals may be in scenarios with Sommerfeld-enhanced annihilation,
subject to the constraint that the dark matter has the correct relic density.
This work refines our previous analysis through detailed treatments of resonant
Sommerfeld enhancement and the effect of Sommerfeld enhancement on freeze out.
Sommerfeld enhancements raise many interesting issues in the freeze out
calculation, and we find that the cutoff of resonant enhancement, the
equilibration of force carriers, the temperature of kinetic decoupling, and the
efficiency of self-interactions for preserving thermal velocity distributions
all play a role. These effects may have striking consequences; for example, for
resonantly-enhanced Sommerfeld annihilation, dark matter freezes out but may
then chemically recouple, implying highly suppressed indirect signals, in
contrast to naive expectations. In the minimal scenario with standard
astrophysical assumptions, and tuning all parameters to maximize the signal, we
find that, for force-carrier mass m_phi = 250 MeV and dark matter masses m_X =
0.1, 0.3, and 1 TeV, the maximal Sommerfeld enhancement factors are S_eff = 7,
30, and 90, respectively. Such boosts are too small to explain both the PAMELA
and Fermi excesses. Non-minimal models may require smaller boosts, but the
bounds on S_eff could also be more stringent, and dedicated freeze out analyses
are required. For concreteness, we focus on 4 mu final states, but we also
discuss 4 e and other modes, deviations from standard astrophysical assumptions
and non-minimal particle physics models, and we outline the steps required to
determine if such considerations may lead to a self-consistent explanation of
the PAMELA or Fermi excesses.Comment: 31 pages, published versio
Analytical solutions to the spin-1 Bose-Einstein condensates
We analytically solve the one-dimensional coupled Gross-Pitaevskii equations
which govern the motion of F=1 spinor Bose-Einstein condensates. The nonlinear
density-density interactions are decoupled by making use of the unique
properties of the Jacobian elliptical functions. Several types of complex
stationary solutions are deduced. Furthermore, exact non-stationary solutions
to the time-dependent Gross-Pitaevskii equations are constructed by making use
of the spin-rotational symmetry of the Hamiltonian. The spin-polarizations
exhibit kinked configurations. Our method is applicable to other coupled
nonlinear systems.Comment: 12 figure
Quantum Trajectory Approach to Molecular Dynamics Simulation with Surface Hopping
The powerful molecular dynamics (MD) simulation is basically based on a
picture that the atoms experience classical-like trajectories under the
exertion of classical force field determined by the quantum mechanically solved
electronic state. In this work we propose a quantum trajectory approach to the
MD simulation with surface hopping, from an insight that an effective
"observation" is actually implied in theMDsimulation through tracking the
forces experienced, just like checking the meter's result in the quantum
measurement process. This treatment can build the nonadiabatic surface hopping
on a dynamical foundation, instead of the usual artificial and conceptually
inconsistent hopping algorithms. The effects and advantages of the proposed
scheme are preliminarily illustrated by a two-surface model system.Comment: 6 pages, 3 figure
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