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

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 $SU(2)_L$ triplet and one singlet Higgs fields, leads to a scenario in which the see-saw mechanism is realized with the Majorana mass $M_R$ 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 $\rho=1$ at tree level even when their vacuum expectation values (VEV) which determine the value of $M_R$, can be as large as the electroweak scale. $M_R$ is found to obey the bound $\frac{M_Z}{2} \leq M_R < 246 GeV$ which makes it accessible experimentally (Tevatron, LHC or ILC) since, in our scenario, $\nu_R$'s can couple directly to the Standard Model (SM) gauge bosons.Comment: 5 double-column pages. Version to appear in Phys. Lett.

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

Complete CKM quark mixing via dimensional deconstruction

It is shown that the deconstruction of $[SU(2)\times U(1)]^N$ into $[SU(2)\times U(1)]$ 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, μ→eγ\mu \to e \gamma and τ→μγ\tau \to \mu \gamma

The Lepton Flavour Violating (LFV) processes $\mu \to e \gamma$ and $\tau \to \mu \gamma$ are estimated in a model of electroweak-scale right-handed neutrinos. The present bounds on the branching ratios, $B(\mu \to e \gamma)< 1.2 \times 10^{-11}$, $B(\tau \to \mu \gamma) < 6.8 \times 10^{-8}$ (BaBar) and $< 4.5 \times 10^{-8}$ (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 $\Lambda_{FP}$ in the range of a few TeV to the order of $10^2$ TeV, above which the Higgs quartic and Yukawa couplings become practically constant. We found that around $\Lambda_{FP}$ 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, $a_Z$, of a spontaneously broken global $U(1)_{A}^{(Z)}$ symmetry whose potential is induced by the instantons of a new gauge group $SU(2)_Z$. The $SU(2)_Z$ coupling becomes large at a scale $\Lambda_Z \sim 10^{-3} eV$ starting from an initial value $M$ at high energy which is of the order of the Standard Model (SM) couplings at the same scale $M$. A perspective on a possible unification of $SU(2)_Z$ with the SM will be briefly discussed. We present a scenario in which $a_Z$ is trapped in a false vacuum characterized by an energy density $\sim (10^{-3} eV)^4$. 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 $a_Z$ 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