arXiv subjects

R. Nevzorov

Publications and source records attributed to R. Nevzorov.

At least 37 records · Page 2Linked to original sources

arXiv2015

Exploring the CP-violating NMSSM: EDM Constraints and Phenomenology

The Next-to-Minimal Supersymmetric extension of the Standard Model (NMSSM) features extra new sources for CP violation. In contrast to the MSSM CP violation can already occur at tree level in the Higgs sector. We investigate the range of possible allowed CP-violating phases by taking into account the constraints arising from the measurements of the Electric Dipole Moments (EDMs) and the latest LHC Higgs data. Our analysis shows that large CP-violating phases, that are NMSSM-specific, are not in conflict with the EDMs. They are dominantly constrained by the Higgs data in this case. We use our results to investigate the prospects of measuring CP violation through the combined measurement of Higgs rates, on the one hand, and in observables based on CP-violating Higgs couplings to tau leptons on the other hand.

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arXiv2015

E6 inspired composite Higgs model

We consider a composite Higgs model embedded into a Grand Unified Theory(GUT) based on the E_6 gauge group. The phenomenological viability of this E_6 inspired composite Higgs model (E6CHM) implies that standard model (SM) elementary fermions with different baryon or lepton number should stem from different 27 representations of E_6. We present a six-dimensional orbifold GUT model in which the E_6 gauge symmetry is broken to the SM gauge group so that the appropriate splitting of the bulk 27-plets takes place. In this model the strongly coupled sector is localised on one of the branes and possesses an SU(6) global symmetry that contains the SU(3)_C\times SU(2)_W\times U(1)_Y subgroup. In this case the approximate gauge coupling unification can be attained if the right-handed top quark is a composite state and the elementary sector involves extra exotic matter beyond the SM which ensures anomaly cancellation. The breakdown of the approximate SU(6) symmetry at low energies in this model results in a set of the pseudo-Nambu-Goldstone states which include a Higgs doublet and scalar colour triplet. We discuss the generation of the masses of the SM fermions in the E6CHM. The presence of the TeV scale vector-like exotic quarks and scalar colour triplet may provide spectacular new physics signals that can be observed at the LHC.

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arXiv2014

Non-Standard Higgs Decays in U(1) Extensions of the MSSM

In U(1) extensions of the Minimal Supersymmetric extension of the Standard Model there is a simple mechanism that leads to a heavy Z' boson with a mass which is substantially larger than the supersymmetry breaking scale. This mechanism may also result in a pseudoscalar state that is light enough for decays of the 125 GeV Standard Model-like Higgs boson into a pair of such pseudoscalars to be kinematically allowed. We study these decays within E6 inspired supersymmetric models with an exact custodial symmetry that forbids tree-level flavor-changing transitions and the most dangerous baryon and lepton number violating operators. We argue that the branching ratio of the lightest Higgs boson decays into a pair of the light pseudoscalar states may not be negligibly small.

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arXiv2014

Nonstandard Higgs decays in the E6 inspired SUSY models

We consider the exotic decays of the SM-like Higgs state within the E6 inspired supersymmetric (SUSY) models. In these models the lightest SUSY particle (LSP) can be substantially lighter than 1 eV forming hot dark matter in the Universe. The next--to--lightest SUSY particle (NLSP) also tend to be light. We argue that the NLSP with GeV scale mass may lead to the substantial branching ratio of the nonstandard decays of the SM-like Higgs boson into NLSPs.

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arXiv2014

On the smallness of the cosmological constant

In N=1 supergravity the scalar potential of the hidden sector may have degenerate supersymmetric (SUSY) and non-supersymmetric Minkowski vacua. In this case local SUSY in the second supersymmetric Minkowski phase can be broken dynamically. Assuming that such a second phase and the phase associated with the physical vacuum are exactly degenerate, we estimate the value of the cosmological constant. We argue that the observed value of the dark energy density can be reproduced if in the second vacuum local SUSY breaking is induced by gaugino condensation at a scale which is just slightly lower than Λ_{QCD} in the physical vacuum. The presence of a third degenerate vacuum, in which local SUSY and electroweak (EW) symmetry are broken near the Planck scale, may lead to small values of the quartic Higgs self--coupling and the corresponding beta function at the Planck scale in the phase in which we live.

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arXiv2014

Cosmological constant in SUGRA models with Planck scale SUSY breaking and degenerate vacua

The empirical mass of the Higgs boson suggests small to vanishing values of the quartic Higgs self--coupling and the corresponding beta function at the Planck scale, leading to degenerate vacua. This leads us to suggest that the measured value of the cosmological constant can originate from supergravity (SUGRA) models with degenerate vacua. This scenario is realised if there are at least three exactly degenerate vacua. In the first vacuum, associated with the physical one, local supersymmetry (SUSY) is broken near the Planck scale while the breakdown of the SU(2)_W\times U(1)_Y symmetry takes place at the electroweak (EW) scale. In the second vacuum local SUSY breaking is induced by gaugino condensation at a scale which is just slightly lower than Λ_{QCD} in the physical vacuum. Finally, in the third vacuum local SUSY and EW symmetry are broken near the Planck scale.

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arXiv2014

Discovery Prospects for NMSSM Higgs Bosons at the High-Energy Large Hadron Collider

We investigate the discovery prospects for NMSSM Higgs bosons during the 13~TeV run of the LHC. While one of the neutral Higgs bosons is demanded to have a mass around 125~GeV and Standard Model (SM)-like properties, there can be substantially lighter, nearby or heavier Higgs bosons, that have not been excluded yet by LEP, Tevatron or the 8~TeV run of the LHC. The challenge consists in discovering the whole NMSSM Higgs mass spectrum. We present the rates for production and subsequent decay of the neutral NMSSM Higgs bosons in the most promising final states and discuss their possible discovery. The prospects for pinning down the Higgs sector of the Natural NMSSM will be analysed taking into account alternative search channels. We give a series of benchmark scenarios compatible with the experimental constraints, that feature Higgs-to-Higgs decays and entail (exotic) signatures with multi-fermion and/or multi-photon final states. These decay chains furthermore give access to the trilinear Higgs self-couplings. We briefly discuss the possibility of exploiting coupling sum rules in case not all the NMSSM Higgs bosons are discovered.

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arXiv2014

Quasi-fixed point scenarios and the Higgs mass in the E6 inspired SUSY models

We analyse the two-loop renormalization group (RG) flow of the gauge and Yukawa couplings within the E6 inspired supersymmetric (SUSY) models with extra U(1)_{N} gauge symmetry under which right-handed neutrinos have zero charge. In these models single discrete \tilde{Z}^{H}_2 symmetry forbids the tree-level flavor-changing transitions and the most dangerous baryon and lepton number violating operators. We consider two different scenarios A and B that involve extra matter beyond the MSSM contained in three and four 5+\overline{5} representations of SU(5) respectively plus three SU(5) singlets which carry U(1)_{N} charges. In the scenario A the measured values of the SU(2)_W and U(1)_Y gauge couplings lie near the fixed points of the RG equations. In the scenario B the contribution of two--loop corrections spoils the unification of gauge couplings resulting in the appearance of the Landau pole below the Grand Unification scale M_X. The solutions for the Yukawa couplings also approach the quasi fixed points with increasing their values at the scale M_X. We calculate the two--loop upper bounds on the lightest Higgs boson mass in the vicinity of these quasi fixed points and compare the results of our analysis with the corresponding ones in the NMSSM. In all these cases the theoretical restrictions on the SM--like Higgs boson mass are rather close to 125 GeV.

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arXiv2013

Exotic Higgs decays in the E6 inspired SUSY models

We study the decays of the SM-like Higgs state within the E6 inspired supersymmetric (SUSY) models with exact custodial symmetry that forbids tree-level flavor-changing transitions and the most dangerous baryon and lepton number violating operators. In these models there are two states which are absolutely stable and can contribute to the dark matter density. One of them is the lightest SUSY particle (LSP) which is expected to be lighter than 1 eV forming hot dark matter in the Universe. The presence of another stable neutral state allows to account for the observed cold dark matter density. In the considered SUSY models next-to-lightest SUSY particle (NLSP) also tend to be light. We argue that the NLSP with GeV scale mass can result in the substantial branching ratio of the nonstadard decays of the lightest Higgs boson.

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arXiv2012

E6 inspired SUSY models with exact custodial symmetry

The breakdown of E_6 gauge symmetry at high energies may lead to supersymmetric (SUSY) models based on the Standard Model (SM) gauge group together with extra U(1)_ψ and U(1)_χ gauge symmetries. To ensure anomaly cancellation the particle content of these E_6 inspired models involves extra exotic states that generically give rise to non-diagonal flavour transitions and rapid proton decay. We argue that a single discrete \tilde{Z}^{H}_2 symmetry can be used to forbid tree-level flavor-changing transitions, as well as the most dangerous baryon and lepton number violating operators. We present 5D and 6D orbifold GUT constructions that lead to the E_6 inspired SUSY models of this type. The breakdown of U(1)_ψ and U(1)_χ gauge symmetries that preserves E_6 matter parity assignment guarantees that ordinary quarks and leptons and their superpartners, as well as the exotic states which originate from 27 representations of E_6 survive to low energies. These E_6 inspired models contain two dark-matter candidates and must also include additional TeV scale vectorlike lepton or vectorlike down type quark states to render the lightest exotic quark unstable. We examine gauge coupling unification in these models and discuss their implications for collider phenomenology and cosmology.

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arXiv2012

Constrained Exceptional Supersymmetric Standard Model with a Higgs Near 125 GeV

We study the parameter space of the constrained exceptional supersymmetric standard model (cE6SSM) consistent with a Higgs signal near 125 GeV and the LHC searches for squarks, gluinos and Z'. The cE6SSM parameter space consistent with correct electroweak symmetry breaking, is represented by scans in the (m0, M1/2) plane for fixed Z' mass and tan beta, with squark, gluino and Higgs masses plotted as contours in this plane. We find that a 125 GeV Higgs mass only arises for a sufficiently large Z' mass, mostly above current limits, and for particular regions of squark and gluino masses corresponding to multi-TeV squark masses, but with lighter gluinos typically within reach of the LHC 8 TeV or forthcoming 14 TeV runs. Successful dark matter relic abundance may be achieved over all the parameter space, assuming a bino-like LSP with a nearby heavier inert Higgsino doublet and decoupled inert singlinos, resulting in conventional gluino decay signatures. A set of typical benchmark points with a Higgs near 125 GeV is provided which exemplifies these features.

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arXiv2012

NMSSM Higgs Benchmarks Near 125 GeV

The recent LHC indications of a SM-like Higgs boson near 125 GeV are consistent not only with the Standard Model (SM) but also with Supersymmetry (SUSY). However naturalness arguments disfavour the Minimal Supersymmetric Standard Model (MSSM). We consider the Next-to-Minimal Supersymmetric Standard Model (NMSSM) with a SM-like Higgs boson near 125 GeV involving relatively light stops and gluinos below 1 TeV in order to satisfy naturalness requirements. We are careful to ensure that the chosen values of couplings do not become non perturbative below the grand unification (GUT) scale, although we also examine how these limits may be extended by the addition of extra matter to the NMSSM at the two-loop level. We then propose four sets of benchmark points corresponding to the SM-like Higgs boson being the lightest or the second lightest Higgs state in the NMSSM or the NMSSM-with-extra-matter. With the aid of these benchmark points we discuss how the NMSSM Higgs boson near 125 GeV may be distinguished from the SM Higgs boson in future LHC searches.

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arXiv2011

Phenomenological aspects of Supersymmetry: SUSY models and electroweak symmetry breaking

These lectures are a very brief introduction to low energy supersymmetry (SUSY). The approach to the construction of SUSY Lagrangians based on the superfield formalism is considered. The minimal supersymmetric standard model (MSSM) is specified. The breakdown of gauge symmetry and Higgs phenomenology within the simplest SUSY extensions of the standard model (SM) are briefly reviewed. The upper bound on the mass of the lightest Higgs boson and little hierarchy problem in SUSY models are discussed.

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arXiv2011

Nonstandard Higgs Decays and Dark Matter in the E6SSM

We study the decays of the lightest Higgs boson within the exceptional supersymmetric (SUSY) standard model (E6SSM). The E6SSM predicts three families of Higgs-like doublets plus three SM singlets that carry U(1)_{N} charges. One family of Higgs-like doublets and one SM singlet develop vacuum expectation values. The fermionic partners of other Higgs-like fields and SM singlets form inert neutralino and chargino states. Two lightest inert neutralinos tend to be the lightest and next-to-lightest SUSY particles (LSP and NLSP). The considered model can account for the dark matter relic abundance if the lightest inert neutralino has mass close to half the Z mass. In this case the usual SM-like Higgs boson decays more than 95% of the time into either LSPs or NLSPs. As a result the decays of the lightest Higgs boson into l^{+} l^{-} + X might play an essential role in the Higgs searches. This scenario also predicts other light inert chargino and neutralino states below 200 GeV and large LSP direct detection cross-sections which is on the edge of observability of XENON100.

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arXiv2011

Dark Energy density in models with Split Supersymmetry and degenerate vacua

In N=1 supergravity supersymmetric (SUSY) and non-supersymmetric Minkowski vacua originating in the hidden sector can be degenerate. In the supersymmetric phase in flat Minkowski space non-perturbative supersymmetry breakdown may take place in the observable sector, inducing a non-zero and positive vacuum energy density. Assuming that such a supersymmetric phase and the phase in which we live are degenerate, we estimate the value of the cosmological constant. We argue that the observed value of the dark energy density can be reproduced in the Split-SUSY scenario of the supersymmetry breaking if the SUSY breaking scale is of order of 10^{10} GeV.

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arXiv2011

Collider phenomenology of the E6SSM

We consider collider signatures of the exceptional supersymmetric (SUSY) standard model (E6SSM). This E6 inspired SUSY model is based on the SM gauge group together with an extra U(1) gauge symmetry under which right--handed neutrinos have zero charge. To ensure anomaly cancellation and gauge coupling unification the low energy matter content of the E6SSM involve extra exotic matter beyond the MSSM. We discuss the collider signatures associated with the production of new particles predicted by the E6SSM and consider the implications of this model for dark matter and Higgs phenomenology. Since exotic quarks in the E6SSM can be either diquarks or leptoquarks they may provide spectacular new physics signals at the LHC.

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arXiv2011

LHC Signatures of the Constrained Exceptional Supersymmetric Standard Model

We discuss two striking Large Hadron Collider (LHC) signatures of the constrained version of the exceptional supersymmetric standard model (cE6SSM), based on a universal high energy soft scalar mass m_0, soft trilinear coupling A_0 and soft gaugino mass M_{1/2}. The first signature we discuss is that of light exotic colour triplet charge 1/3 fermions, which we refer to as D-fermions. We calculate the LHC production cross section of D-fermions, and discuss their decay patterns. Secondly we discuss the E6 type U(1)_N spin-1 Z' gauge boson and show how it may decay into exotic states, increasing its width and modifying the line shape of the dilepton final state. We illustrate these features using two representative cE6SSM benchmark points, including an "early LHC discovery" point, giving the Feynman rules and numerical values for the relevant couplings in order to facilitate further studies.

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arXiv2011

Novel Higgs Decays and Dark Matter in the E(6)SSM

The Exceptional Supersymmetric (SUSY) Standard Model predicts three families of Higgs doublets plus three Higgs singlets, where one family develops vacuum expectation values (VEVs), while the remaining two which do not are called Inert. The model can account for the dark matter relic abundance if the two lightest Inert neutralinos, identified as the (next-to) lightest SUSY particles ((N)LSPs), have masses close to half the Z mass. In this case we find that the usual SM-like Higgs boson decays more than 95% of the time into either LSPs or NLSPs. The latter case produces a final state containing two leptons l^{+}l^{-} with an invariant mass less than or about 10 GeV. We illustrate this scenario with a set of benchmark points satisfying phenomenological constraints and the WMAP dark matter relic abundance. This scenario also predicts other light Inert chargino and neutralino states below 200 GeV, and large LSP direct detection cross-sections close to current limits and observable soon at XENON100.

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