42,741 research outputs found
Fermion Portal Dark Matter
We study a class of simplified dark matter models in which one dark matter
particle couples with a mediator and a Standard Model fermion. In such models,
collider and direct detection searches probe complimentary regions of parameter
space. For Majorana dark matter, direct detection covers the region near
mediator-dark matter degeneracy, while colliders probe regions with a large
dark matter and mediator mass splitting. For Dirac and complex dark matter,
direct detection is effective for the entire region above the mass threshold,
but colliders provide a strong bound for dark matter lighter than a few GeV. We
also point out that dedicated searches for signatures with two jets or a
mono-jet not coming from initial state radiation, along missing transverse
energy can cover the remaining parameter space for thermal relic dark matter.Comment: 22 pages, 10 figures; corrections made on coannihilation parts,
references added; corrections made on Majorana fermion direct detectio
Large N (=3) Neutrinos and Random Matrix Theory
The large N limit has been successfully applied to QCD, leading to
qualitatively correct results even for N=3. In this work, we propose to treat
the number N=3 of Standard Model generations as a large number. Specifically,
we apply this idea to the neutrino anarchy scenario and study neutrino physics
using Random Matrix Theory, finding new results in both areas. For neutrino
physics, we obtain predictions for the masses and mixing angles as a function
of the generation number N. The Seesaw mechanism produces a hierarchy of order
1/N^3 between the lightest and heaviest neutrino, and a theta(13) mixing angle
of order 1/N, in parametric agreement with experimental data when N goes to 3.
For Random Matrix Theory, this motivates the introduction of a new type of
ensemble of random matrices, the "Seesaw ensemble." Basic properties of such
matrices are studied, including the eigenvalue density and the interpretation
as a Coulomb gas system. Besides its mathematical interest, the Seesaw ensemble
may be useful in random systems where two hierarchical scales exist.Comment: 20 pages, 6 figures, 1 table; accepted version for JHEP, references
adde
Detecting Axion Stars with Radio Telescopes
When axion stars fly through an astrophysical magnetic background, the
axion-to-photon conversion may generate a large electromagnetic radiation
power. After including the interference effects of the spacially-extended
axion-star source and the macroscopic medium effects, we estimate the radiation
power when an axion star meets a neutron star. For a dense axion star with
, the radiated power is at the order of
10^{11}\,\mbox{W}\times(100\,\mu\mbox{eV}/m_a)^4\,(B/10^{10}\,\mbox{Gauss})^2
with as the axion particle mass and the strength of the neutron star
magnetic field. For axion stars occupy a large fraction of dark matter energy
density, this encounter event with a transient \mathcal{O}(0.1\,\mbox{s})
radio signal may happen in our galaxy with the averaged source distance of one
kiloparsec. The predicted spectral flux density is at the order of Jy for
a neutron star with Gauss. The existing Arecibo, GBT, JVLA and
FAST and the ongoing SKA radio telescopes have excellent discovery potential of
dense axion stars.Comment: 16 pages, 2 figure
Lepton Portal Dark Matter
We study a class of simplified dark matter models in which dark matter
couples directly with a mediator and a charged lepton. This class of Lepton
Portal dark matter models has very rich phenomenology: it has loop generated
dark matter electromagnetic moments that generate a direct detection signal; it
contributes to indirect detection in the cosmic positron flux via dark matter
annihilation; it provides a signature of the same-flavor, opposite-sign
dilepton plus missing transverse energy at colliders. We determine the current
experimental constraints on the model parameter space for Dirac fermion,
Majorana fermion and complex scalar dark matter cases of the Lepton Portal
framework. We also perform a collider study for the 14 TeV LHC reach with 100
inverse femtobarns for dark matter parameter space. For the complex scalar dark
matter case, the LHC provides a very stringent constraint and its reach can be
interpreted as corresponding to a limit as strong as two tenths of a zeptobarn
on the dark matter-nucleon scattering cross section for dark matter masses up
to 500 GeV. We also demonstrate that one can improve the current collider
searches by using a Breit-Wigner like formula to fit the dilepton MT2 tail of
the dominant diboson background.Comment: 24 pages, 8 figure
Coloron-assisted Leptoquarks at the LHC
Recent searches for a first-generation leptoquark by the CMS collaboration
have shown around 2.5 sigma deviations from Standard Model predictions in both
the eejj and e nu jj channels. Furthermore, the eejj invariant mass
distribution has another 2.8 sigma excess from the CMS right-handed W plus
heavy neutrino search. We point out that additional leptoquark production from
a heavy coloron decay can provide a good explanation for all three excesses.
The coloron has a mass around 2.1 TeV and the leptoquark mass can vary from 550
GeV to 650 GeV. A key prediction of this model is an edge in the total m_T
distribution of e nu jj events at around 2.1 TeV.Comment: 5 pages, 4 figure
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