1,157 research outputs found
Leptoquarks, Dark Matter, and Anomalous LHC Events
Leptoquarks with mass in the region of GeV are a possible candidate
for the recent excess seen by CMS in the and channels. We
discuss models where leptoquarks decay primarily to dark matter and jets,
thereby giving a branching to charged lepton and jet final states that can
match data. The confluence of proton decay constraints, dark matter indirect
and direct detection data, and Higgs invisible decay bounds results in a
handful of predictive models that will be conclusively verified or excluded in
upcoming direct detection experiments. Along the way, we present robust limits
on such leptoquark models stemming from the muon magnetic moment using current
and projected experiment sensitivities, as well as from and meson
mixing, and leptonic and semi-leptonic meson decays.Comment: Section on muon g-2 and references updated. 9 pages, 6 figure
Thermal production of gravitinos
We reconsider thermal production of gravitinos in the early universe, adding to previously considered 2 -> 2 gauge scatterings: a) production via 1 -> 2 decays, allowed by thermal masses; b) the effect of the top Yukawa coupling; c) a proper treatment of the reheating process. Our final result behaves physically (larger couplings give a larger rate) and is twice larger than previous results, implying e.g. a twice stronger constraint on the reheating temperature. Accessory results about (supersymmetric) theories at finite temperature and gravitino couplings might have some interest
Relating leptogenesis parameters to light neutrino masses
We obtain model independent relations among neutrino masses and leptogenesis
parameters. We find exact relations that involve the CP asymmetries
, the washout parameters and
, and the neutrino masses and , as well
as powerful inequalities that involve just and . We
prove that the Yukawa interactions of at least two of the heavy singlet
neutrinos are in the strong washout region ().Comment: 5 pages, 1 figur
Z′ models for the LHCb and g-2 muon anomalies
We revisit a class of Z' explanations of the anomalies found by the LHCb
collaboration in decays, and show that the scenario is tightly constrained
by a combination of constraints: (i) LHC searches for di-muon resonances, (ii)
pertubativity of the Z' couplings; (iii) the mass difference, and (iv)
and electro-weak precision data. Solutions are found by suppressing the Z'
coupling to electrons and to light quarks and/or by allowing for a Z' decay
width into dark matter. We also present a simplified framework where a
TeV-scale Z' gauge boson that couples to standard leptons as well as to new
heavy vector-like leptons, can simultaneously accommodate the LHCb anomalies
and the muon g-2 anomaly
Multi-muon events at the Tevatron: a hidden sector from hadronic collisions
Intrigued by some features of a small but significant fraction of the
multi-muon events recently published by the CDF collaboration, we show an
explicit attempt to describe them in terms of a light scalar singlet
which communicates with the standard quarks either through a heavy scalar or a
heavy fermion exchange. As suggested in arXiv:0810.7530, the singlet has
a chain decay into a final state made of four pairs. We can
simulate most of the muon properties of the selected sample of events. Some of
these properties adhere rather well to the already published data; others
should allow a decisive test of the proposed interpretation. Assuming that the
test is positively passed, we show how the PAMELA excess can be fitted by the
annihilation of a TeV Dark Matter particle that communicates with the Standard
Model via the new light singlet(s).Comment: 19 pp, v2: small changes, agrees with the published versio
Massive and Massless Neutrinos on Unbalanced Seesaws
The observation of neutrino oscillations requires new physics beyond the
standard model (SM). A SM-like gauge theory with p lepton families can be
extended by introducing q heavy right-handed Majorana neutrinos but preserving
its SU(2)_L x U(1)_Y gauge symmetry. The overall neutrino mass matrix M turns
out to be a symmetric (p+q) x (p+q) matrix. Given p>q, the rank of M is in
general equal to 2q, corresponding to 2q non-zero mass eigenvalues. The
existence of (p-q) massless left-handed Majorana neutrinos is an exact
consequence of the model, independent of the usual approximation made in
deriving the Type-I seesaw relation between the effective p x p light Majorana
neutrino mass matrix M_\nu and the q x q heavy Majorana neutrino mass matrix
M_R. In other words, the numbers of massive left- and right-handed neutrinos
are fairly matched. A good example to illustrate this seesaw fair play rule is
the minimal seesaw model with p=3 and q=2, in which one massless neutrino sits
on the unbalanced seesaw.Comment: RevTex 8 pages, 1 PS figure. Two crucial references adde
Muon and Tau Neutrinos Spectra from Solar Flares
Solar neutrino flares and mixing are considered. Most power-full solar flare
as the ones occurred on 23th February 1956, September 29th 1989, 28th October
and on 2nd-4th November 2003 are sources of cosmic rays, X, gamma and neutrino
bursts. These flares took place both on front or in the edge and in the hidden
solar disk. The observed and estimated total flare energy should be a source of
a prompt secondary neutrino burst originated, by proton-proton-pion production
on the sun itself; a more delayed and spread neutrino flux signal arise by the
solar charged flare particles reaching the terrestrial atmosphere. Our first
estimates of neutrino signals in largest underground detectors hint for few
events in correlation with, gamma,radio onser. Our approximated spectra for
muons and taus from these rare solar eruption are shown over the most common
background. The muon and tau signature is very peculiar and characteristic over
electron and anti-electron neutrino fluxes. The rise of muon neutrinos will be
detectable above the minimal muon threshold of 113 MeV. The rarest tau
appearence will be possible only for hardest solar neutrino energies above
3.471 GeVComment: 14 pages, 4 figures, Vulcano Conference 200
Anthropic solution to the magnetic muon anomaly: the charged see-saw
We present models of new physics that can explain the muon g-2 anomaly in
accord with with the assumption that the only scalar existing at the weak scale
is the Higgs, as suggested by anthropic selection. Such models are dubbed
"charged see-saw" because the muon mass term is mediated by heavy leptons. The
electroweak contribution to the g-2 gets modified by order one factors, giving
an anomaly of the same order as the observed hint, which is strongly correlated
with a modification of the Higgs coupling to the muon.Comment: 21 pages, many equations despite the first word in the title. v3:
loop function G_WN corrected, conclusions unchange
Neutrino Masses, Lepton Flavor Mixing and Leptogenesis in the Minimal Seesaw Model
We present a review of neutrino phenomenology in the minimal seesaw model
(MSM), an economical and intriguing extension of the Standard Model with only
two heavy right-handed Majorana neutrinos. Given current neutrino oscillation
data, the MSM can predict the neutrino mass spectrum and constrain the
effective masses of the tritium beta decay and the neutrinoless double-beta
decay. We outline five distinct schemes to parameterize the neutrino
Yukawa-coupling matrix of the MSM. The lepton flavor mixing and baryogenesis
via leptogenesis are investigated in some detail by taking account of possible
texture zeros of the Dirac neutrino mass matrix. We derive an upper bound on
the CP-violating asymmetry in the decay of the lighter right-handed Majorana
neutrino. The effects of the renormalization-group evolution on the neutrino
mixing parameters are analyzed, and the correlation between the CP-violating
phenomena at low and high energies is highlighted. We show that the observed
matter-antimatter asymmetry of the Universe can naturally be interpreted
through the resonant leptogenesis mechanism at the TeV scale. The
lepton-flavor-violating rare decays, such as , are also
discussed in the supersymmetric extension of the MSM.Comment: 50 pages, 22 EPS figures, macro file ws-ijmpe.cls included, accepted
for publication in Int. J. Mod. Phys.
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