arXiv subjects

Goran Senjanovic

Publications and source records attributed to Goran Senjanovic.

At least 37 records · Page 2Linked to original sources

arXiv2011

Problems with False Vacua in Supersymmetric Theories

It has been suggested recently that in a consistent theory any Minkowski vacuum must be exactly stable. As a result, a large class of theories that in ordinary treatment would appear sufficiently long-lived, in reality make no sense. In particular, this applies to supersymmetric models in which global supersymmetry is broken in a false vacuum. We show that in any such theory the dynamics of supersymmetry breaking cannot be decoupled from the Planck scale physics. This finding poses an obvious challenge for the idea of low-scale metastable (for example gauge) mediation.

hep-th↗

arXiv2011

Probing the Origin of Neutrino Mass: from GUT to LHC

Ever since the Majorana classic work, the nature of neutrino has been one of the central questions of the weak interaction physics. If neutrino is its own antiparticle, the immediate consequence is lepton number violation through the neutrinoless double beta decay. However, colliders such as the LHC offer a hope of seeing directly the same phenomenon, and moreover the Majorana nature of new particles needed to complete the Standard Model. I review here the salient features of these phenomena, and then turn to grand unification as a way of probing the scale of the relevant new physics. The minimal supersymmetric SO(10) theory basically eliminates the LHC physics, but leads naturally to the large atmospheric mixing angle and furthermore predicts $θ_{13} \simeq 10^\circ$ without any additional symmetries, in agreement with new T2K and MINOS data. It also assures that the R-parity is exact and thus leads to the stable LSP as a natural Dark Matter candidate. The minimal realistic SU(5) theory, on the other hand, predicts the light fermion triplet, below TeV, as a source of neutrino Majorana mass.

hep-ph↗

arXiv2011

Inert Doublet Dark Matter and Mirror/Extra Families after Xenon100

It was shown recently that mirror fermions, naturally present in a number of directions for new physics, seem to require an inert scalar doublet in order to pass the electroweak precision tests. This provides a further motivation for considering the inert doublet as a dark matter candidate. Moreover, the presence of extra families enhances the Standard Model Higgs-nucleon coupling, which has crucial impact on the Higgs and dark matter searches. We study the limits on the inert dark matter mass in view of recent Xenon100 data. We find that the mass of the inert dark matter must lie in a very narrow window 74-76 GeV while the Higgs must weigh more than 400 GeV. For the sake of completeness we discuss the cases with fewer extra families, where the possibility of a light Higgs boson opens up, enlarging the dark matter mass window to m_h/2-76 GeV. We find that Xenon100 constrains the DM-Higgs interaction, which in turn implies a lower bound on the monochromatic gamma-ray flux from DM annihilation in the galactic halo. For the mirror case, the predicted annihilation cross section lies a factor of 4-5 below the current limit set by Fermi LAT, thus providing a promising indirect detection signal.

hep-ph↗

arXiv2011

Seesaw at LHC through Left - Right Symmetry

I argue that LHC may shed light on the nature of neutrino mass through the probe of the seesaw mechanism. The smoking gun signature is lepton number violation through the production of same sign lepton pairs, a collider analogy of the neutrinoless double beta decay. I discuss this in the context of L-R symmetric theories, which led originally to neutrino mass and the seesaw mechanism. A W_R gauge boson with a mass in a few TeV region could easily dominate neutrinoless double beta decay, and its discovery at LHC would have spectacular signatures of parity restoration and lepton number violation. Moreover, LHC can measure the masses of the right-handed neutrinos and the right-handed leptonic mixing matrix, which could in turn be used to predict the rates for neutrinoless double decay and lepton flavor violating violating processes. The LR scale at the LHC energies offers great hope of observing these low energy processes in the present and upcoming experiments.

hep-ph↗

arXiv2010

Naturally Light Sterile Neutrinos from Theory of R-parity

The fate of R-parity is one of the central issues in the minimal supersymmetric standard model (MSSM). Gauged $B-L$ symmetry provides a natural framework for addressing this question. Recently, it was pointed out that the minimal such theory does not need any additional Higgs if the $B-L$ breaking is achieved through the VEVs of right-handed sneutrinos, which ties the new physics scale to the scale of the MSSM. We show here that this immediately leads to an important prediction of two light sterile neutrinos, which can play a significant role in the BBN and neutrino oscillations. We also discuss some new relevant phenomenology for the LHC, in the context of the minimal supersymmetric left-right symmetric theory which provides a natural setting for the gauged $B-L$ symmetry.

hep-ph↗

arXiv2010

MSSM in view of PAMELA and Fermi-LAT

We take the MSSM as a complete theory of low energy phenomena, including neutrino masses and mixings. This immediately implies that the gravitino is the only possible dark matter candidate. We study the implications of the astrophysical experiments such as PAMELA and Fermi-LAT, on this scenario. The theory can account for both the realistic neutrino masses and mixings, and the PAMELA data as long as the slepton masses lie in the $500-10^6 $TeV range. The squarks can be either light or heavy, depending on their contribution to radiative neutrino masses. On the other hand, the Fermi-LAT data imply heavy superpartners, all out of LHC reach, simply on the grounds of the energy scale involved, for the gravitino must weigh more than 2 TeV. The perturbativity of the theory also implies an upper bound on its mass, approximately $6-7 $TeV.

hep-ph↗

arXiv2010

Left-Right Symmetry at LHC

We revisit the issue of the limit on the scale of Left-Right symmetry breaking. We focus on the minimal SU(2)_L x SU(2)_R x U(1)_B-L gauge theory with the seesaw mechanism and discuss the two possibilities of defining Left-Right symmetry as parity or charge conjugation. In the commonly adopted case of parity, we perform a complete numerical study of the quark mass matrices and the associated left and right mixing matrices without any assumptions usually made in the literature about the ratio of vacuum expectation values. We find that the usual lower limit on the mass of the right-handed gauge boson from the K mass difference, M_WR>2.5TeV, is subject to a possible small reduction due to the difference between right and left Cabibbo angles. In the case of charge conjugation the limit on M_WR is somewhat more robust. However, the more severe bounds from CP-violating observables are absent in this case. In fact, the free phases can also resolve the present mild discrepancy between the Standard Model and CP-violation in the $B$-sector. Thus, even in the minimal case, both charged and neutral gauge bosons may be accessible at the Large Hadron Collider with spectacular signatures of lepton number violation.

hep-ph↗

arXiv2010

Type II see-saw dominance in SO(10)

Grand unified theories where the neutrino mass is given by Type II seesaw have the potential to provide interesting connections between the neutrino and charged fermion sectors. We explore the possibility of having a dominant Type II seesaw contribution in supersymmetric SO(10). We show that this can be achieved in the model where symmetry breaking is triggered by 54 and 45-dimensional representations, without the need for additional fields other than those already required to have a realistic charged fermion mass spectrum. Physical consequences, such as the implementation of the BSV mechanism, the possibility of the fields responsible for Type II see-saw dominance being messengers of supersymmetry breaking, and the realization of baryo and leptogenesis in this theories are discussed.

hep-ph↗

arXiv2010

LHC and the origin of neutrino mass

It is often said that neutrino mass is a window to a new physics beyond the standard model (SM). This is certainly true if neutrinos are Majorana particles since the SM with Majorana neutrino mass is not a complete theory. The classical text-book test of neutrino Majorana mass, the neutrino-less double beta decay depends on the completion, and thus cannot probe neutrino mass. As pointed out already more than twenty five years ago, the colliders such as Tevatron or LHC offer a hope of probing directly the origin of neutrino Majorana mass through lepton number violating production of like sign lepton pairs. I discuss this in the context of all three types of seesaw mechanism. I then discuss in detail the situation in $L-R$ symmetric theories, which led originally to the seesaw and which incorporates naturally both type I and type II. A $W_R$ gauge boson with a mass in a few TeV region could easily dominate the neutrino-less double beta decay, and its discovery at LHC would have spectacular signatures of parity restoration and lepton number violation. At the end I give an example of a predictive SU(5) grand unified theory that results in a hybrid type I and III seesaw with a light fermion triplet below TeV scale.

hep-ph↗

arXiv2009

Proton decay and grand unification

I review the theoretical and experimental status of proton decay theory and experiment. Regarding theory, I focus mostly, but not only, on grand unification. I discuss only the minimal, well established SU(5) and SO(10) models, both ordinary and supersymmetric. I show how the minimal realistic extensions of the original Georgi - Glashow model can lead to interesting LHC physics, and I demonstrate that the minimal supersymmetric SU(5) theory is in perfect accord with experiment. Since no universally accepted model has of yet emerged, I discuss the effective operator analysis of proton decay and some related predictions from a high scale underlying theory. A strong case is made for the improvement of experimental limits, or better the search of, two body neutron decay modes into charged kaons and charged leptons. Their discovery would necessarily imply a low energy physics since they practically vanish in any theory with a desert in energies between M_W and M_GUT.

hep-ph↗

arXiv2009

Probing leptonic CP phases in LFV processes

We study a CP and T violating triple (spin) correlation in the muon to electron conversion in nuclei in the context of the seesaw mechanism. After concluding that the results are negative for all three seesaw types, we turn to the left-right symmetric theories as the original source of seesaw. We find that in general this correlation is of order one which offers a hope of observing CP violation in lepton flavor violating processes for a L-R scale below around 10-30 TeV. We discuss the conditions that could render to (unlikely) conspiracies as to suppress the CP violating effects.

hep-ph↗

arXiv2009

Collider Signatures for Heavy Lepton Triplet in Type I+III Seesaw

The minimal SU(5) theory augmented by the fermionic adjoint representation restores the coupling constant unification and gives realistic neutrino masses and mixing through the hybrid Type I and Type III seesaw. The crucial prediction of the theory is an SU(2) lepton triplet with the mass below TeV. We study the signature of these heavy leptons and propose the strategy to test this mechanism at the hadron and lepton colliders. The smoking gun evidence of the theory is Delta L=2 lepton number violation through events of a pair of like-sign leptons plus four jets without significant missing energy at hadron colliders. We find that via this unique channel, the heavy lepton can be searched for up to a mass of 200 GeV at the Tevatron with 8 fb^-1, and up to 450 (700) GeV at the LHC of 14 TeV C.M.energy with 10 (100) fb^-1. The signal rate at the 10 TeV LHC is reduced to 60-35% for a mass of 200-700 GeV. We also comment on how to distinguish this theory from other models with similar heavy leptons. Finally, we compare the production rates and angular distributions of heavy leptons in e+e- collisions for various models.

hep-ph↗

arXiv2007

Probing seesaw at LHC

We have recently proposed a simple SU(5) theory with an adjoint fermionic multiplet on top of the usual minimal spectrum. This leads to the hybrid scenario of both type I and type III seesaw and it predicts the existence of the fermionic SU(2) triplet between 100 GeV and 1 TeV for a conventional GUT scale of about 10^{16} GeV, with main decays into W (Z) and leptons, correlated through Dirac Yukawa couplings, and lifetimes shorter than about 10^{-12} sec. These decays are lepton number violating and they offer an exciting signature of Delta L=2 dilepton events together with 4 jets at future pp (p\bar p) colliders. Increasing the triplet mass endangers the proton stability and so the seesaw mechanism could be directly testable at LHC.

hep-ph↗

arXiv2007

Seesaw at LHC

We study the implementation of the type III seesaw in the ordinary nonsupersymmetric SU(5) grand unified theory. This allows for an alternative definition of the minimal SU(5) model, with the inclusion of the adjoint fermionic multiplet. The main prediction of the theory is the light fermionic SU(2) triplet with mass at the electroweak scale. Due to their gauge couplings, these triplets can be produced pair-wise via Drell-Yan, and due to the Majorana nature of the neutral component their decays leave a clear signature of same sign di-leptons and four jets. This allows for their possible discovery at LHC and provides an example of directly measurable seesaw parameters.

hep-ph↗

arXiv2006

SO(10): a theory of fermion masses and mixings

SO(10) grand unified theory seems to have all the ingredients to be a complete unified theory of quarks and leptons. I review here its minimal, possibly realistic versions, both supersymmetric and not.

hep-ph↗

arXiv2006

Proton decay, supersymmetry breaking and its mediation

We study the breaking of supersymmetry and its transmission to the light states in the context of the minimal SU(5) grand unified theory, with no additional singlets. This simple theory can be taken as a prototype for a program of breaking simultaneously grand unified symmetry and supersymmetry. The main predictions are: (i) d=6 proton decay is completely negligible and d=5 is in accord with experiment, (ii) supersymmetry breaking is mainly mediated by gravity.

hep-ph↗

arXiv2005

Fermion mass relations in a supersymmetric SO(10) theory

Neutrino and charged fermion masses provide important constraints on grand unified theories. We illustrate this by focusing on a renormalizable, supersymmetric SO(10) theory proposed long ago, that recently attracted great interest in view of its minimality. We show how the nature of the light Higgs, which depends on the GUT scale fields, gets reflected on the precise predictions for fermion masses and mixings. We exemplify this on the case of dominant Type II see-saw, which gets severely constrained and is likely to fail.

hep-ph↗

arXiv2005

Yukawa sector in non-supersymmetric renormalizable SO(10)

We discuss the ordinary, non-supersymmetric SO(10) as a theory of fermion masses and mixings. We construct two minimal versions of the Yukawa sector based on $\bar{126}_H $ and either $10_H$ or $120_H$. The latter case is of particular interest since it connects the absolute neutrino mass scale with the size of the atmospheric mixing angle $θ_A$. It also relates the smallness of $V_{cb}$ with the largeness of $θ_A$. These results are based on the analytic study of the second and third generations. Furthermore, we discuss the structure of the light Higgs and the role of the Peccei-Quinn symmetry for dark matter and the predictivity of the theory.

hep-ph↗