315 research outputs found
A Higgs Quadruplet for Type III Seesaw and Implications for and Conversion
In Type III seesaw model the heavy neutrinos are contained in leptonic
triplet representations. The Yukawa couplings of the triplet fermion and the
left-handed neutrinos with the doublet Higgs field produce the Dirac mass
terms. Together with the Majorana masses for the leptonic triplets, the light
neutrinos obtain non-zero seesaw masses. We point out that it is also possible
to have a quadruplet Higgs field to produce the Dirac mass terms to facilitate
the seesaw mechanism. The vacuum expectation value of the quadruplet Higgs is
constrained to be small by electroweak precision data. Therefore the Yukawa
couplings of a quadruplet can be much larger than those for a doublet. We also
find that unlike the usual Type III seesaw model where at least two copies of
leptonic triplets are needed, with both doublet and quadruplet Higgs
representations, just one leptonic triplet is possible to have a
phenomenologically acceptable model because light neutrino masses can receive
sizable contributions at both tree and one loop levels. Large Yukawa couplings
of the quadruplet can induce observable effects for lepton flavor violating
processes and conversion. Implications of the
recent limit from MEG and also limit on conversion
on Au are also given. Some interesting collider signatures for the doubly
charged Higgs boson in the quadruplet are discussed.Comment: Latex 11 pages, 1 figure. A few references adde
Oxygen-induced p(2x3) reconstruction on Mo(112) studied by LEED and STM
The open trough-and-row Mo(112) surface serves as substrate for the epitaxial growth of MoO2. In the early stage of oxygen exposure, oxygen chemisorption induces a p(2x3) surface reconstruction of the missing row type on Mo(112). The surface structure of this reconstructed surface has been studied in detail by low-energy electron diffraction and scanning tunneling microscope. The experimental findings can be explained based on the effective medium theory for oxygen adsorption on transition-metal surfaces, providing a structure model for the oxygen-modified Mo(112) surface. The structure model allows the discussion of the oxygen-chemisorbed surface phase as a possible precursor state fo
Bounds on neutrino masses from leptogenesis in type-II see-saw models
The presence of the triplet in left-right symmetric theories
leads to type-II see-saw mechanism for the neutrino masses. In these models,
assuming a normal mass hierarchy for the heavy Majorana neutrinos, we derive a
lower bound on the mass of the lightest of heavy Majorana neutrino from the
leptogenesis constraint. From this bound we establish a consistent picture for
the hierarchy of heavy Majorana neutrinos in a class of left right symmetric
models in which we identify the neutrino Dirac mass matrix with that of
Fritzsch type charged lepton mass matrix. It is shown that these values are
compatible with the current neutrino oscillation data.Comment: minor typos corrected, references added, match with published versio
Leptogenesis Bound on Spontaneous Symmetry Breaking of Global Lepton Number
We propose a new class of leptogenesis bounds on the spontaneous symmetry
breaking of global lepton number. These models have a generic feature of
inducing new lepton number violating interactions, due to the presence of the
Majorons. We analyzed the singlet Majoron model with right-handed neutrinos and
find that the lepton number should be broken above 10^5 GeV to realize a
successful leptogenesis because the annihilations of the right-handed neutrinos
into the massless Majorons and into the standard model Higgs should go out of
equilibrium before the sphaleron process is over. We then argue that this type
of leptogenesis constraint should exist in the singlet-triplet Majoron models
as well as in a class of R-parity violating supersymmetric Majoron models.Comment: 4 pages, 2 figure
The chemical composition of globular clusters in the Local Group
We present detailed abundance measurements for 45 globular clusters (GCs) in
galaxies in (and, in one case, beyond) the Local Group. The measurements are
based on new high-resolution integrated-light spectra of GCs in NGC 185, NGC
205, M31, M33, and NGC 2403, combined with reanalysis of previous observations
of GCs in the Fornax dSph, WLM, NGC 147, NGC 6822, and the Milky Way. The GCs
cover the range -2.8 < [Fe/H] < -0.1 and we determined abundances for Fe, Na,
Mg, Si, Ca, Sc, Ti, Cr, Mn, Ni, Cu, Zn, Zr, Ba, and Eu. Corrections for non
local thermodynamic equilibrium effects are included for Na, Mg, Ca, Ti, Mn,
Fe, Ni, and Ba. For several of the galaxies, our measurements provide the first
quantitative constraints on the detailed composition of their metal-poor
stellar populations. Overall, the GCs in different galaxies exhibit remarkably
uniform abundance patterns of the alpha-, iron-peak, and neutron-capture
elements, with a dispersion of less than 0.1 dex in [alpha/Fe] for the full
sample. There is a hint that GCs in dwarf galaxies are slightly less
alpha-enhanced (by about 0.04 dex on average) than those in larger galaxies.
One GC in M33 (HM33-B) resembles the most metal-rich GCs in the Fornax dSph
(Fornax 4) and NGC 6822 (SC7) by having alpha-element abundances closer to
scaled-solar values, possibly hinting at an accretion origin. We find that the
alpha-element abundances strongly correlate with those of Na, Sc, Ni, and Zn.
Several GCs with [Fe/H]<-1.5 are deficient in Mg compared to other
alpha-elements. We find no GCs with strongly enhanced r-process abundances as
reported for metal-poor stars in some ultra-faint dwarfs and the Magellanic
Clouds. The similarity of the abundance patterns for metal-poor GCs in
different environments points to similar early enrichment histories and only
allow for minor variations in the initial mass function.Comment: 34 pages + 6 appendices. Accepted for publication in Astronomy &
Astrophysic
Probing top charged-Higgs production using top polarization at the Large Hadron Collider
We study single top production in association with a charged Higgs in the
type II two Higgs doublet model at the Large Hadron Collider. The polarization
of the top, reflected in the angular distributions of its decay products, can
be a sensitive probe of new physics in its production. We present theoretically
expected polarizations of the top for top charged-Higgs production, which is
significantly different from that in the closely related process of t-W
production in the Standard Model. We then show that an azimuthal symmetry,
constructed from the decay lepton angular distribution in the laboratory frame,
is a sensitive probe of top polarization and can be used to constrain
parameters involved in top charged-Higgs production.Comment: 22 pages, 18 Figures, Discussions about backgrounds and NLO
corrections added, figures modified, references added, Version published in
JHE
Population III X-ray Binaries and their Impact on the Early Universe
The first population of X-ray binaries (XRBs) is expected to affect the
thermal and ionization states of the gas in the early Universe. Although these
X-ray sources are predicted to have important implications for high-redshift
observable signals, such as the hydrogen 21-cm signal from cosmic dawn and the
cosmic X-ray background, their properties are poorly explored, leaving
theoretical models largely uninformed. In this paper we model a population of
X-ray binaries arising from zero metallicity stars. We explore how their
properties depend on the adopted initial mass function (IMF) of primordial
stars, finding a strong effect on their number and X-ray production efficiency.
We also present scaling relations between XRBs and their X-ray emission with
the local star formation rate, which can be used in sub-grid models in
numerical simulations to improve the X-ray feedback prescriptions.
Specifically, we find that the uniformity and strength of the X-ray feedback in
the intergalactic medium is strongly dependant on the IMF. Bottom-heavy IMFs
result in a smoother distribution of XRBs, but have a luminosity orders of
magnitude lower than more top-heavy IMFs. Top-heavy IMFs lead to more spatially
uneven, albeit strong, X-ray emission. An intermediate IMF has a strong X-ray
feedback while sustaining an even emission across the intergalactic medium.
These differences in X-ray feedback could be probed in the future with
measurements of the cosmic dawn 21-cm line of neutral hydrogen, which offers us
a new way of constraining population III IMF.Comment: Accepted for publication in MNRAS, 17 pages, 9 figure
Low energy consequences from supersymmetric models with left-right symmetry
We consider several low energy consequences arising from a class of
supersymmetric models based on the gauge groups and in which the gauge
hierarchy and problems have been resolved. There are important
constraints on the MSSM parameters , and
, and we discuss how they are reconciled with radiative electroweak
breaking. We also consider the ensuing sparticle and Higgs spectroscopy, as
well as the decays and . The latter process
may be amenable to experimental tests through an order of magnitude increase in
sensitivity.Comment: 17 pages, latex2
Do experiments suggest a hierarchy problem?
The hierarchy problem of the scalar sector of the standard model is
reformulated, emphasizing the role of experimental facts that may suggest the
existence of a new physics large mass scale, for instance indications of the
instability of the matter, or indications in favor of massive neutrinos. In the
see-saw model for the neutrino masses a hierarchy problem arises if the mass of
the right-handed neutrinos is larger than approximatively GeV: this
problem, and its possible solutions, are discussed.Comment: revtex, 4 pages, 1 figur
Minimal Supersymmetric Pati-Salam Theory: Determination of Physical Scales
We systematically study the minimal supersymmetric Pati-Salam theory, paying
special attention to the unification constraints. We find that the SU(4)_c
scale M_c and the Left-Right scale M_R lie in the range 10^{10} GeV < M_c <
10^{14} GeV, 10^{3} GeV < M_R <10^{10} GeV (with single-step breaking at
10^{10} GeV), giving a potentially accessible scale of parity breaking. The
theory includes the possibility of having doubly-charged supermultiplets at the
supersymmetry breaking scale; color octet states with mass of order M_R^2/M_c;
magnetic monopoles of intermediate mass that do not conflict with cosmology,
and a 'clean' (type I) form for the see-saw mechanism of neutrino mass.Comment: 5 page
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