In this talk, I discuss how we may approach physics at the seesaw- and GUT-scales using data from the TeV scale. Even though we cannot hope to directly reach these energy scales using particle accelerators, we may get convinced of grand unification and seesaw mechanism based on experimental data if Nature is kind to us. In addition, we may find compelling reason to believe in leptogenesis based on experimental data. This cannot be achieved by a single experiment, but rather a collection of them, based on LHC, ILC, neutrino oscillation, neutrinoless double beta decay, direct dark matter detection, CMB power spectrum and its tensor mode.
Alternative renormalizable minimal non-SUSY SO(10) GUT model is proposed. Instead of a ${\bf 126}$-dimensional Higgs field, a ${\bf 120}$-dimensional Higgs filed is ntroducedin addition to a ${\bf 10}$-dimensional Higgs field and plays a crucial role to reproduce the realistic charged fermion mass matrices. With contributions of ${\bf 120}$ Higgs field, the original Witten's scenario of inducing the right-handed Majorana neutrino mass through 2-loop diagrams becomes phenomenologically viable. This model inherits the nice features of the conventional renormalizable minimal SO(10) GUT model with…
Till today lepton flavor violation has not been observed in processes involving charged leptons. Hence, a search for it is under hot pursuit both in theories and experiments. In our current work, we investigate the rates of rare decay processes such as $τ\rightarrow μγ$ in SU(5) SUSY GUT and found that it satisfies the current bound and is one order below the projected sensitivity. This gives a corroborative argument for the influence of the large top-Yukawa coupling at the GUT scale ($λ_{tG}$) on flavor violating decay rates of leptons which are investigable at low energy electroweak scale $M…
The importance of the mass spectroscopy of the superparticles is emphasized. It will be shown that the gauge coupling constants give us information on the GUT-scale mass spectrum once the superparticle masses are known. The gaugino masses will provide us a model-independent test of the grand unification irrespective of the symmetry breaking pattern. The sfermion masses carry the information on the intermediate symmetries, if present. Combining the mass spectrum, we will be able to distinguish among the GUT models, and hopefully supergravity models also.
The minimal SUSY SO(10) GUT models with {\bf 10}, {\bf 126} and {\bf 210} Higgs and only renormalizable couplings has been shown to provide a simple way to understand the neutrino mixings as well as the ratio $Δm^2_\odot/Δm^2_A$ in terms of quark mixing parameter $θ_{Cabibbo}$, provided neutrino masses are described by type II seesaw formula. However, in this minimal picture, it is impossible to realize type II dominance with renormalizable couplings in 4-dimensions. We show that this problem can be cured by embedding this model into a warped 5-dimensional space time with warping between the P…
In this work we consider a simple extension of the Standard Model involving additional fermionic singlets and assume an underlying inverse seesaw mechanism (with one or more right-handed neutrinos and one or more sterile fermions) for neutrino mass generation. Under the assumption that both sterile states and right-handed neutrinos are present, our goal is to determine which is the minimal inverse seesaw realisation that accounts for neutrino data while at the same time complying with all experimental requirements (electroweak precision tests and laboratory constraints). This study aims at ide…
We calculate the relic density of the lightest neutralino in a supersymmetric seesaw type-II (``triplet seesaw'') model with minimal supergravity boundary conditions at the GUT scale. The presence of a triplet below the GUT scale, required to explain measured neutrino data in this setup, leads to a characteristic deformation of the sparticle spectrum with respect to the pure mSugra expectations, affecting the calculated relic dark matter (DM) density. We discuss how the DM allowed regions in the (m_0,M_{1/2}) plane change as a function of the (type-II) seesaw scale. We also compare the constra…
We show that Supersymmetric models with Type I seesaw neutrino masses support slow roll inflection point inflation. The inflaton is the D-flat direction labelled by the chiral invariant HLN composed of the Higgs(H), slepton(L) and conjugate sneutrino(N) superfields. The scale of inflation and fine tuning is set by the conjugate neutrino Majorana mass $M_{ν^c} \sim 10^6-10^{12}$ GeV. The cubic term in the (quartic) inflaton potential is dominantly from superpotential (not soft Susy breaking) couplings. The tuning conditions are thus insensitive to soft supersymmetry breaking parameters and are …
Supersymmetric SO(10) grand unified models with renormalizable Yukawa couplings involving {\bf 10}, {\bf 126} and {\bf 120} Higgs fields have been shown to give a very economical theory for understanding quark-lepton flavor in a unified framework. In previous papers, we showed how nucleon decay can be suppressed in these models without invoking cancellation, by choice of Yukawa flavor texture within a type II seesaw framework for neutrinos that explains all mixings and masses including the recently observed "large" $θ_{13}$. In this follow-up paper, we extend our earlier work to the case of ty…
We recapitulate the latest results on the class of the simplest SO(10) grand unified models in which the GUT-scale symmetry breaking is triggered by an adjoint Higgs representation. We argue that the minimal survival approximation traditionally used in the GUT- and seesaw-scale estimates tends to be blind to very interesting parts of the parameter space in which some of the intermediate-scale states necessary for non-supersymmetric unification of the SM gauge couplings can be as light as to leave their imprints in the TeV domain. The stringent minimal-survival-based estimates of the B-L scale …
We study the production of heavy neutrinos at the Large Hadron Collider (LHC) through the dominant s-channel production mode as well as the vector boson fusion (VBF) process. We consider the TeV scale minimal linear seesaw model containing two heavy singlets with opposite lepton number. This model is fully reconstructible from oscillation data apart from an overall normalization constant which can be constrained from meta-stability of the electroweak vacuum and bounds coming from lepton flavor violation (LFV) searches. Dirac nature of heavy neutrinos in this model implies suppression of the co…
We discuss a GUT realization of the supersymmetric triplet seesaw mechanism(recently proposed by us in hep-ph/0604083 and further analyzed in hep-ph/0607298) where the exchange of the heavy triplet states generates both neutrino masses and soft SUSY breaking terms.
Radiative corrections to neutrino mixings in seesaw models depend on the nature of new physics between the weak and the GUT-seesaw scales and can be taken into account using the renormalization group equations. This new physics effect becomes particularly important for models with quasi-degenerate neutrino masses where small neutrino mixings at the seesaw scale can get magnified by radiative renormalization effects alone to match observations. This mechanism of radiative magnification which provides a simple understanding of why lepton mixings are so different from quark mixings was demonstrat…
We study a $μ- τ$ reflection symmetry in neutrino sector realized at the GUT scale in the context of the seesaw model. In our scenario, the exact $μ- τ$ reflection symmetry realized in the basis where the charged lepton and heavy Majorana mass matrices are diagonal, leads to vanishing lepton asymmetries. We find that, in the minimal supersymmetry extension of the seesaw model with appropriate values of $\tanβ$, the renormalization group (RG) evolution from the GUT scale to seesaw scale can induce a successful leptogenesis. It is shown that the right amount of the baryon asymmetries $η_B$ can b…
We examine whether an appreciable value of the lepton flavor mixing angle $θ_{13}$ at the electroweak scale $Λ_{\rm EW}$ can be radiatively generated from $θ_{13} = 0^\circ$ at the GUT scale $Λ_{\rm GUT}$. It is found that the renormalization-group running and seesaw threshold effects may lead to $θ_{13} \sim 5^\circ$ at low energies for two simple large-maximal mixing patterns of the MNS matrix in the minimal supersymmetric standard model. If $θ_{12}$ is sufficiently large at $Λ_{\rm GUT}$, it will be possible to radiatively produce $θ_{13} \sim 5^\circ$ at $Λ_{\rm EW}$ both in the standard m…
We consider a $μ-τ$ symmetry in neutrino sectors realized at GUT scale in the context of a seesaw model. In our scenario, the exact $μ-τ$ symmetry realized in the basis where the charged lepton and heavy Majorana neutrino mass matrices are diagonal leads to vanishing lepton asymmetries. We find that, in the minimal supersymmetric extension of the seesaw model with large $\tanβ$, the renormalization group (RG) evolution from GUT scale to seesaw scale can induce a successful leptogenesis even without introducing any symmetry breaking terms by hand, whereas such RG effects lead to tiny deviations…
We discuss the implications of large neutrino mixings for grand unified theories based on the seesaw mechanism. In SU(5) GUTs large mixings can be accomodated by means of $U(1)_F$ flavour symmetries. In these models the heavy Majorana neutrinos are essentially decoupled from low energy neutrino physics. On the contrary in SO(10) GUTs large neutrino mixings severely constrain the mass spectrum of the heavy Majorana neutrinos. This leads to predictions for a variety of observables in neutrino physics as well as for the cosmological baryon asymmetry.
We demonstrate how a class of non-supersymmetric $SO(10)$ GUT with asymmetric left-right theory $SU(2)_L \times U(1)_R \times U(1)_{B-L} \times SU(3)_C$ and Pati-Salam theory $SU(2)_L \times SU(2)_R \times SU(4)_C$ as intermediate symmetry breaking steps leads to successful gauge coupling unification satisfying proton decay constraints. The motivation behind this work is two fold: firstly to study the renormalization group evolution equations for gauge couplings by keeping right-handed neutral gauge boson $Z_R$ around LHC energy range leading interesting dilepton searches at collider while fix…
I discuss a renormalisable model based on $Δ(27)$ family symmetry with an $SO(10)$ grand unified theory (GUT) with spontaneous geometrical $CP$ violation. The symmetries are broken close to the GUT breaking scale, yielding the minimal supersymmetric standard model. Low-scale Yukawa structure is dictated by the coupling of matter to $ Δ(27) $ antitriplets $ \barϕ $ whose vacuum expectation values are aligned in the CSD3 directions by the superpotential. Light physical Majorana neutrinos masses emerge from the seesaw mechanism within $SO(10)$. The model predicts a normal neutrino mass hierarchy …
After a quarter of century of intense search for new physics beyond the Standard Model (SM), two ideas stand out to naturally cope with (i) small neutrino masses and (ii) a light higgs boson : Seesaw and SUSY. The combination of these two ideas, i.e. SUSY seesaw exhibits a potentially striking signature: a strong (or even very strong) enhancement of lepton flavour violation (LFV), which on the contrary remains unobservable in the SM seesaw. Indeed, even when supersymmetry breaking is completely flavour blind, Renormalisation Group running effects are expected to generate large lepton flavour v…
The see-saw mechanism is a very attractive explanation for small neutrino masses, parametrized at the GUT scale by the right-handed Majorana mass matrix, ${\cal M}$, and the neutrino Yukawa matrix, ${\bf Y_ν}$. We show that in a SUSY model with universal soft terms, ${\cal M}$ and ${\bf Y_ν}$ can be calculated from the light neutrino masses, the MNS matrix, and ${\bf Y^{\dagger}_ν} {\bf Y_ν}$, which enters into the left-handed slepton radiative corrections. This suggests that in principle the GUT-scale inputs of the seesaw could be reconstructed from the neutrino and sneutrino mass matrices. W…
Any new neutrino physics at the TeV scale must include a suppression mechanism to keep its contribution to light neutrino masses small enough. We review some seesaw model examples with weakly broken lepton number, and comment on the expected effects at large colliders and in neutrino oscillations.
We investigate how the baryon asymmetry of our universe via leptogenesis can be achieved within the framework of the seesaw model with Fritzsch type lepton mass matrices proposed by Fukugita $et. al$. We study the cases with CP-violating phases in charged lepton Yukawa matrix, however, with and without Dirac neutrino Yukawa phases. We consider both flavor independent and flavor dependent leptogenesis, and demonstrate how they lead to different amounts of lepton asymmetries in detail. In particular, it is shown that flavor dependent leptogenesis in this model can be worked out only when the CP …
Simple extensions of the Standard Model (SM) with additional Right Handed Neutrinos (RHNs) can elegantly explain the existence of small neutrino masses and their flavor mixings. Collider searches for sterile neutrinos are being actively pursued currently. Heavy RHNs may dominantly decay into $W^\pm l^\pm$ after being produced at the LHC. In this paper, we consider collider signatures of heavy pseudo-Dirac neutrinos in the context of inverse seesaw scenario, with a sizable mixing with the SM neutrinos under two different flavor structures, viz., Flavor Diagonal (FD) and Flavor Non-Diagonal (FND…
We consider an exact mu-tau reflection symmetry in neutrino sectorrealized at the GUT scale in the context of the seesaw model with and without supersymmetry. Assuming the two lighter heavy Majorana neutrinos are degenerate at the GUT scale, it is shown that the renormalization group (RG) evolution from the GUT scale to the seesaw scale gives rise to breaking of the mu-tau symmetry and a tiny splitting between two degenerate heavy Majorana neutrino masses as well as small variations of the CP phases in Y_nu, which are essential to achieve a successful leptogenesis. Such small RG effects lead t…
We discuss a class of left-right symmetric models where the light neutrino masses originate dominantly from type I seesaw mechanism along with a sub-dominant type II seesaw contribution. The dominant type I seesaw gives rise to tri-bimaximal type neutrino mixing whereas sub-dominant type II seesaw acts as a small perturbation giving rise to non-zero $θ_{13}$ in our model which also has TeV scale right-handed neutrinos and $Z^\prime$ gauge boson thereby making the model verifiable at current accelerator experiments. Sub-dominant type II and dominant type I seesaw can be naturally accommodated b…
We discuss the issue of vacuum stability of standard model by embedding it within the TeV scale left-right universal seesaw model (called SLRM in the text). This model has only two coupling parameters $(λ_1, λ_2)$ in the Higgs potential and only two physical neutral Higgs bosons $(h, H)$. We explore the range of values for $(λ_1, λ_2)$ for which the light Higgs boson mass $M_h=126$ GeV and the vacuum is stable for all values of the Higgs fields. Combining with the further requirement that the scalar self couplings remain perturbative till typical GUT scales of order $10^{16}$ GeV, we find (i) …
In this letter we address the issue of generating appropriate tiny neutrino masses within the framework of a particular $SU(3)_{c}\otimes SU(3)_{L}\otimes U(1)_{X}$ gauge model by adding three singlet exotic Majorana neutrinos to the ones included in the three lepton triplet representations. The theoretical device is the general method of treating gauge models with high symmetries $SU(3)_{c}\otimes SU(N)_{L}\otimes U(1)_{X}$ proposed by Cotăescu more than a decade ago. When it is worked-out in the 3-3-1 model it supplies a unique free parameter ($a$) to be tuned in order to get a realistic mas…
We propose a grand unified SU(5)$\times$U(1)$_X$ model, where the standard SU(5) grand unified theory is supplemented by minimal seesaw and a right-handed neutrino dark matter with an introduction of a global $Z_2$-parity. In the presence of three right-handed neutrinos (RHNs), the model is free from all gauge and mixed-gravitational anomalies. The SU(5) symmetry is broken into the Standard Model (SM) gauge group at $M_{\rm GUT} \simeq 4 \times 10^{16}$ GeV in the standard manner, while the U(1)$_X$ symmetry breaking occurs at the TeV scale, which generates the TeV-scale mass of the U(1)$_X$ g…
A detailed analytic and numerical study of baryogenesis through leptogenesis is performed in the framework of the standard model of electroweak interactions extended by the addition of three right-handed neutrinos, leading to the seesaw mechanism. We analyze the connection between GUT-motivated relations for the quark and lepton mass matrices and the possibility of obtaining a viable leptogenesis scenario. In particular, we analyze whether the constraints imposed by SO(10) GUTs can be compatible with all the available solar, atmospheric and reactor neutrino data and, simultaneously, be capable…
Recently realization of TeV scale inverse seesaw mechanism in supersymmetric SO(10) framework has led to a number of experimentally verifiable predictions including low-mass W_R and Z' gauge bosons and nonunitarity effects. Using nonsupersymmetric SO(10) grand unified theory, we show how a TeV scale inverse seesaw mechanism for neutrino masses is implemented with a low-mass Z' boson accessible to Large Hadron Collider. We derive renormalization group equations for fermion masses and mixings in the presence of the intermediate symmetries of the model and extract the Dirac neutrino mass matrix a…
We survey some recent ideas and progress in looking for particle physics beyond the Standard Model, connected by the theme of Supersymmetry (SUSY). We review the success of SUSY-GUT models, the expected experimental signatures and present limits on SUSY partner particles, and Higgs phenomenology in the minimal SUSY model.
In this talk, I discuss recent developments concerning the possibility of large extra spacetime dimensions. After briefly reviewing how such dimensions can lower the fundamental GUT, Planck, and string scales, I then outline how these scenarios lead to a new higher-dimensional seesaw mechanism for generating neutrino oscillations --- perhaps even without neutrino masses. I also discuss how extra dimensions lead to new mechanisms contributing to the ``invisibility'' of the QCD axion. This talk reports on work done in collaboration with Emilian Dudas and Tony Gherghetta.
In the last few years physicists have been looking at $SO(10)$ GUT models with renewed attention because it has been realized that the SU(5) minimal model cannot unify the strong, electromagnetic and weak interactions in a way consistent with the experimental values of $α(M_Z)$, $\si$ and $α_S(M_Z)$. In this paper we derive lower limits on neutrino masses, relevant for cosmology and for the solar-neutrino problem, from necessary consistency conditions on a class of $SO(10)$ models with $\sq$ or $\stt$ intermediate gauge symmetry.
The modern theories of Grand Unification (GUT) and supersymmetric (SUSY) extensions of standard model (SM) suppose that the conservation laws of the SM may be violated to some small degree. The nuclei are well-suited as a laboratory to test fundamental symmetries and fundamental interactions like lepton flavor (LF) and lepton number (LN) conservation. A prominent role between experiments looking for LF and total LN violation play yet not observed processes of neutrinoless double beta decay. The GUT's and SUSY models offer a variety of mechanisms which allow this process to occur. They are base…
