70 research outputs found
A new mechanism for a naturally small Dirac neutrino mass
A mechanism is proposed in which a right-handed neutrino zero mode and a
right-handed charged lepton zero mode can be localized at the same place along
an extra compact dimension while having markedly different spreads in their
wave functions: a relatively narrow one for the neutrino and a rather broad one
for the charged lepton. In their overlaps with the wave function for the
left-handed zero modes, this mechanism could produce a natural large hierarchy
in the effective Yukawa couplings in four dimensions, and hence a large
disparity in masses.Comment: 6 pages (2 with figures), twocolumn forma
The relic density of shadow dark matter candidates
We present the results of relic density calculations for cold dark matter
candidates coming from a model of dark energy and dark matter, which is
described by an asymptotically free gauge group SU(2)_Z (QZD) with a coupling
constant alpha_Z ~ 1 at very low scale of Lambda_Z ~ 10^(-3) eV while alpha_Z ~
weak coupling at high energies. The dark matter candidates of QZD are two
fermions in the form of weakly interacting massive particles. Our results show
that for masses between 50 and 285 GeV, they can account for either a
considerable fraction or the entire dark matter of the Universe.Comment: Revised version after acceptance in NP
A model of electroweak-scale right-handed neutrino mass
If neutrino masses are realized through the see-saw mechanism, can the
right-handed neutrinos be produced and detected at present and future
colliders? The answer is negative in the most popular see-saw scenarios for the
simple reason that they are too heavy in these models. However, a simple
extension of the Standard Model (SM) particle content, including mirror
fermions, two triplet and one singlet Higgs fields, leads to a
scenario in which the see-saw mechanism is realized with the Majorana mass
of the right-handed neutrino being of the order of the electroweak scale
or smaller. A custodial SU(2) symmetry arising from the two triplet Higgs
fields ensures that at tree level even when their vacuum expectation
values (VEV) which determine the value of , can be as large as the
electroweak scale. is found to obey the bound which makes it accessible experimentally (Tevatron, LHC or ILC)
since, in our scenario, 's can couple directly to the Standard Model
(SM) gauge bosons.Comment: 5 double-column pages. Version to appear in Phys. Lett.
Complete CKM quark mixing via dimensional deconstruction
It is shown that the deconstruction of into
is capable of providing all necessary ingredients to
completely impliment the complex CKM mixing of quark flavors. The hierarchical
structure of quark masses originates from the difference in the deconstructed
chiral zero-mode distribution in theory space, while the CP-violating phase
comes from the genuinely complex vacuum expectation value of link fields. The
mixing is constructed in a specific model to satisfy experimental bounds on
quarks' masses and CP violation.Comment: RevTex4, 25 pages, typos in section IIC corrected, published versio
Electroweak-scale mirror fermions, and
The Lepton Flavour Violating (LFV) processes and are estimated in a model of electroweak-scale right-handed
neutrinos. The present bounds on the branching ratios, , (BaBar) and
(Belle), puts strong constraints on the parameters of
the model. This constraint links low energy rare decay processes to high-energy
phenomena (e.g. decay lengths of the mirror charged leptons which are important
in the search for the telltale like-sign dilepton events present in the model
of electroweak-scale right-handed neutrinos).Comment: 8 double-column pages, 1 embedded figure. Version accepted for
publication in Phys. Lett. B includes the following additions: one table, a
few remarks, and three reference
Kaluza-Klein Structure Associated With Fat Brane
It is known that the imposition of orbifold boundary conditions on background
scalar field can give rise to a non-trivial vacuum expectation value (VEV)
along extra dimensions, which in turn generates fat branes and associated
unconventional Kaluza-Klein (KK) towers of fermions. We study the structure of
these KK towers in the limit of one large extra dimension and show that
normalizable (bound) states of massless and massive fermions can exist at both
orbifold fixed points. Closer look however indicates that orbifold boundary
conditions act to suppress at least half of bound KK modes, while periodic
boundary conditions tend to drive the high-lying modes to the conventional
structure. By investigating the scattering of fermions on branes, we
analytically compute masses and wavefunctions of KK spectra in the presence of
these boundary conditions up to one-loop level. Implication of KK-number
non-conservation couplings on the Coulomb potential is also examined.Comment: RevTex4, 29 pages, 7 ps figures, new references adde
Renormalization Group Fixed Point with a Fourth Generation: Higgs-induced Bound States and Condensates
In the Standard Model with four generations, the two-loop renormalization
group equations for the Higgs quartic and Yukawa couplings have a fixed point
structure. If the masses of the fourth family are sufficiently heavy, it will
contain a natural scale in the range of a few TeV to the order
of TeV, above which the Higgs quartic and Yukawa couplings become
practically constant. We found that around the strong Yukawa
couplings make it possible for the fourth generation to form bound states,
including composite extra Higgs doublets. In this scenario the fourth
generation condensates are obtained without introducing Technicolor or other
unknown interactions.Comment: 22 pages, 10 figure
New and emerging insect pest and disease threats to forest plantations in Vietnam
The planted forest area in Vietnam increased from 3.0 to 4.4 million hectares in the period 2010–2020, but the loss of productivity from pests and diseases continues to be a problem. During this period, frequent and systematic plantation forest health surveys were conducted on 12 native and 4 exotic genera of trees as well as bamboo across eight forest geographic regions of Vietnam. Damage caused by insects and pathogens was quantified in the field and laboratory in Hanoi. The threats of greatest concern were from folivores (Antheraea frithi, Arthroschista hilaralis, Atteva fabriciella, Hieroglyphus tonkinensis, Lycaria westermanni,Krananda semihyalina, and Moduza procris), wood borers (Batocera lineolata, Euwallacea fornicatus, Tapinolachnus lacordairei, Xyleborus perforans, and Xystrocera festiva), sap-sucking insects (Aulacaspis tubercularis and Helopeltis theivora) and pathogens (Ceratocystis manginecans, Fusarium solani, and Phytophthora acaciivora). The number of new and emerging pests and pathogens increased over time from 2 in 2011 to 17 in 2020, as the damage became more widespread. To manage these pests and diseases, it is necessary to further invest in the selection and breeding of resistant genotypes, improve nursery hygiene and silvicultural operations, and adopt integrated pest management schemes. Consideration should be given to developing forest health monitoring protocols for forest reserves and other special-purpose forests
Brane world unification of quark and lepton masses and its implication for the masses of the neutrinos
A TeV-scale scenario is constructed in an attempt to understand the
relationship between quark and lepton masses. This scenario combines a model of
early (TeV) unification of quarks and leptons with the physics of large extra
dimensions. It demonstrates a relationship between quark and lepton mass scales
at rather ``low'' (TeV) energies which will be dubbed as {\em early
quark-lepton mass unification}. It also predicts that the masses of the
neutrinos are naturally light and Dirac. There is an interesting correlation
between neutrino masses and those of the unconventionally charged fermions
which are present in the early unification model. If these unconventional
fermions were to lie between 200 GeV and 300 GeV, the Dirac neutrino mass scale
is predicted to be between 0.07 eV and 1 eV.Comment: ReVTeX, 16 double-column pages. Typos corrected. One added referenc
A Model of Dark Energy and Dark Matter
A dynamical model for the dark energy is presented in which the
``quintessence'' field is the axion, , of a spontaneously broken global
symmetry whose potential is induced by the instantons of a new
gauge group . The coupling becomes large at a scale
starting from an initial value at high energy
which is of the order of the Standard Model (SM) couplings at the same scale
. A perspective on a possible unification of with the SM will be
briefly discussed. We present a scenario in which is trapped in a false
vacuum characterized by an energy density . The lifetime
of this false vacuum is estimated to be extremely large. Other estimates
relevant to the ``coincidence issue'' include the ages of the universe when the
potential became effective, when the acceleration ``began'' and when the
energy density of the false vacuum became comparable to that of (baryonic and
non-baryonic) matter. Other cosmological consequences include a possible
candidate for the weakly interacting (WIMP) Cold Dark Matter as well as a
scenario for leptogenesis. A brief discussion on possible laboratory detections
of some of the particles contained in the model will also be presented.Comment: 24 double-column pages, 14 figures; Added references; Corrected Typo
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