Searcharxiv⌕ Search

arXiv subjects

Radovan Dermisek

Publications and source records attributed to Radovan Dermisek.

At least 73 records · Page 4Linked to original sources
arXiv2008

Light Charged and CP-odd Higgses in MSSM-like Models

We study the Higgs sector of supersymmetric models containing two Higgs doublets with a light MSSM-like CP odd Higgs, $m_A \lesssim 10$ GeV, and $\tan β\lesssim 2.5$. In this scenario all Higgses resulting from two Higgs doublets: light and heavy CP even Higgses, $h$ and $H$, the CP odd Higgs, $A$, and the charged Higgs, $H^\pm$, could have been produced at LEP or the Tevatron, but would have escaped detection because they decay in modes that have not been searched for or the experiments are not sensitive to. Especially $H \to ZA$ and $H^\pm \to W^{\pm \star} A$ with $A \to c \bar c, τ^+ τ^-$ present an opportunity to discover some of the Higgses at LEP, the Tevatron and also at B factories. In addition, the $2.8 σ$ excess of the branching ratio $W \to τν$ with respect to the other leptons measured at LEP correlates well with the existence of the charged Higgs with properties typical for this scenario. Dominant $τ$- and $c$-rich decay products of all Higgses require modified strategies for their discovery at the LHC.

hep-ph↗
arXiv2008

Light CP-odd Higgs and Small $\tan β$ Scenario in the MSSM and Beyond

We study the Higgs sector of supersymmetric models containing two Higgs doublets with a light MSSM-like CP odd Higgs, $m_A \lesssim 10$ GeV, and $\tan β\lesssim 2.5$. In this scenario all of the Higgses resulting from two Higgs doublets: light and heavy CP even Higgses, $h$ and $H$, the CP odd Higgs, $A$, and the charged Higgs, $H^\pm$, could have been produced at LEP or the Tevatron, but would have escaped detection because they decay in modes that have not been searched for or the experiments are not sensitive to. Especially $H \to ZA$ and $H^\pm \to W^{\pm \star} A$ with $A \to c \bar c, τ^+ τ^-$ present an opportunity to discover some of the Higgses at LEP, the Tevatron and also at B factories. Typical $τ$- and $c$-rich decay products of all Higgses require modified strategies for their discovery at the LHC.

hep-ph↗
arXiv2008

Light Charged Higgs and Lepton Universality in W boson Decays

We study the effect of a light charged Higgs appearing in supersymmetric models containing two Higgs doublets on the measurement of leptonic branching ratios of the W boson at LEP. We show that the $2.8 σ$ excess of the branching ratio $W \to τν$ with respect to the other leptons correlates well with the existence of charged Higgs with mass close to the mass of the W boson which dominantly decays into $W^\star$ and a light CP odd Higgs boson $A$ with mass below $2m_b$, so that it decays into $τ^+ τ^-$ and $c \bar c$. There are no searches for the charged Higgs in this channel and thus it could be discovered in LEP data or at the Tevatron where it would be frequently produced in top quark decays.

hep-ph↗
arXiv2008

Hypercharged Anomaly Mediation

We show that, in string models with the MSSM residing on D-branes, the bino mass can be generated in a geometrically separated hidden sector. Hypercharge mediation thus naturally teams up with anomaly mediation. The mixed scenario predicts a distinctive yet viable superpartner spectrum, provided that the ratio αbetween the bino and gravitino mass lies in the range 0.05 < |α| < 0.25, and m_{3/2} > 35 TeV. We summarize some of the phenomenological features of this scenario.

hep-ph↗
arXiv2008

Nonstandard Higgs Boson Decays

This review summarizes the motivations for and phenomenological consequences of nonstandard Higgs boson decays, with emphasis on final states containing a pair of non-Standard-Model particles that subsequently decay to Standard Model particles. Typically these non-Standard-Model particles are part of a ``hidden'' sector, for example a pair of neutral Higgs bosons or a pair of unstable neutralinos. We emphasize that such decays allow for a Higgs substantially below the Standard Model Higgs LEP limit of 114 GeV. This in turn means that the ``fine-tuning'' problems of many Beyond the Standard Model (BSM) theories, in particular supersymmetric models, can be eliminated while achieving excellent consistency with precision electroweak data which favor a Higgs boson with mass below $100\gev$ and standard $WW$, $ZZ$, and top couplings.

hep-ph↗
arXiv2008

Probing the Stop Sector of the MSSM with the Higgs Boson at the LHC

We propose using the lightest CP-even Higgs boson in the minimal supersymmetric standard model (MSSM) to probe the stop sector. Unlike measuring stop masses in production/decay processes which requires knowledge of masses and mixing angles of other superparticles, the strategy depends little on supersymmetric parameters other than those in the stop sector in a large region of parameter space. We show that measurements of the Higgs mass and the production rate in the gluon fusion channel, the dominant channel at the LHC, allow for determination of two parameters in the stop mass-squared matrix, including the off-diagonal mixing term. This proposal is very effective when stops are light and their mixing is large, which coincides with the region where the electroweak symmetry breaking is minimally fine tuned. We also argue that a lightest CP-even Higgs mass in the upper range of allowed values and a production rate significantly smaller than in the standard model would be difficult to reconcile within the MSSM, except in extreme corners of the parameter space.

hep-ph↗
arXiv2007

The NMSSM Solution to the Fine-Tuning Problem, Precision Electroweak Constraints and the Largest LEP Higgs Event Excess

We present an extended study of how the Next to Minimal Supersymmetric Model easily avoids fine-tuning in electroweak symmetry breaking for a SM-like light Higgs with mass in the vicinity of $100\gev$, as beautifully consistent with precision electroweak data, while escaping LEP constraints due to the dominance of $h\to aa$ decays with $m_a<2m_b$ so that $a\to \tauptaum$ or jets. The residual $\sim 10%$ branching ratio for $h\to b\anti b$ explains perfectly the well-known LEP excess at $\mh\sim 100\gev$. Details of model parameter correlations and requirements are discussed as a function $\tan(β)$. Comparisons of fine-tuning in the NMSSM to that in the MSSM are presented. We also discuss fine-tuning associated with scenarios in which the $a$ is essentially pure singlet, has mass $m_a>30\gev$, and decays primarily to $\gam\gam$ leading to an $h\to aa\to 4\gam$ Higgs signal.

hep-ph↗
arXiv2007

A Comparison of Mixed-Higgs Scenarios In the NMSSM and the MSSM

We study scenarios in the minimal and next-to minimal supersymmetric models in which the lightest CP-even Higgs boson can have mass below the 114 GeV standard model LEP limit by virtue of reduced ZZ coupling due to substantial mixing among the Higgs bosons. We pay particular attention to the size of corrections from superpartners needed for these scenarios to be viable and point to boundary conditions at large scales which lead to these scenarios while at the same time keeping electroweak fine tuning modest in size. We find that naturalness of electroweak symmetry breaking in the mixed-Higgs scenarios of both models points to the same region of soft supersymmetry breaking terms, namely those leading to large mixing in the stop sector at the electroweak scale, especially if we also require that the lightest CP-even Higgs explains the Higgs-like LEP events at about 98 GeV.

hep-ph↗
arXiv2007

The NMSSM Close to the R-symmetry Limit and Naturalness in $h \to aa$ Decays for $m_a<2\mb$

Dominant decay of a SM-like Higgs boson into particles beyond those contained in the minimal supersymmetric standard model has been identified as a natural scenario to avoid fine tuning in electroweak symmetry breaking while satisfying all LEP limits. In the simplest such extension, the next-to-minimal supersymmetric model, the lightest CP-even Higgs boson can decay into two pseudoscalars. In the scenario with least fine tuning the lightest CP-even Higgs boson has mass of order 100 GeV. In order to escape LEP limits it must decay to a pair of the lightest CP-odd Higgs bosons with Br(h -> aa)>.7 and m_a<2m_b (so that a -> τ^+ τ^- or light quarks and gluons). The mass of the lightest CP-odd Higgs boson is controlled by the soft-trilinear couplings, A_λ(m_Z) and A_κ(m_Z). We identify the region of parameter space where this situation occurs and discuss how natural this scenario is. It turns out that in order to achieve m_a < 2 m_b with A_λ(m_Z), A_κ(m_Z) of order the typical radiative corrections, the required tuning of trilinear couplings need not be larger than 5-10 %. Further, the necessity for this tuning can be eliminated in specific SUSY breaking scenarios. Quite interestingly, Br(h -> aa) is typically above 70 % in this region of parameter space and thus an appropriately large value requires no additional tuning.

hep-ph↗
arXiv2007

Mixed Bino-Wino-Higgsino Dark Matter in Gauge Messenger Models

Almost degenerate bino and wino masses at the weak scale is one of unique features of gauge messenger models. The lightest neutralino is a mixture of bino, wino and higgsino and can produce the correct amount of the dark matter density if it is the lightest supersymmetric particle. Furthermore, as a result of squeezed spectrum of superpartners which is typical for gauge messenger models, various co-annihilation and resonance regions overlap and very often the correct amount of the neutralino relic density is generated as an interplay of several processes. This feature makes the explanation of the observed amount of the dark matter density much less sensitive to fundamental parameters. We calculate the neutralino relic density assuming thermal history and present both spin independent and spin dependent cross sections for the direct detection. We also discuss phenomenological constraints from b to s gamma and muon g-2 and compare results of gauge messenger models to well known results of the mSUGRA scenario.

hep-ph↗
arXiv2006

Probing NMSSM Scenarios with Minimal Fine-Tuning by Searching for Decays of the Upsilon to a Light CP-Odd Higgs Boson

Completely natural electroweak symmetry breaking is easily achieved in supersymmetric models if there is a SM-like Higgs boson, $h$, with $m_h\lsim 100\gev$. In the minimal supersymmetric model, such an $h$ decays mainly to $b\anti b$ and is ruled out by LEP constraints. However, if the MSSM Higgs sector is expanded so that $h$ decays mainly to still lighter Higgs bosons, e.g. $h\to aa$, with $BR(h\to aa)>0.7$, and if $m_a<2m_b$, then the LEP constraints are satisfied. In this letter, we show that in the next-to-minimal supersymmetric model the above $h$ and $a$ properties (for the lightest CP-even and CP-odd Higgs bosons, respectively) imply a lower bound on $BR(Υ\to \gam a)$ that dedicated runs at present (and future) $B$ factories can explore.

hep-ph↗
arXiv2006

Naturalness of EWSB in NMSSM and Higgs at 100 GeV

Naturalness of electroweak symmetry breaking in the next-to-minimal supersymmetric model points to scenarios in which the lightest CP-even Higgs boson has SM-like ZZh coupling and mass m_h ~ 100 GeV and decays partly via h -> b \bar b but dominantly into two CP-odd Higgs bosons, h -> aa, where m_a < 2m_b so that a -> tau+ tau- (or light quarks and gluons) decays are dominant. These preferred scenarios correlate well with the observed excess of events at LEP for m_h ~ 100 GeV.

hep-ph↗
arXiv2006

Mediation of Supersymmetry Breaking in Gauge Messenger Models

We study gauge mediation of supersymmetry breaking in SU(5) supersymmetric grand unified theory with gauge fields as messengers. The generated soft supersymmetry breaking parameters lead to close to maximal mixing scenario for the Higgs mass and highly reduce the fine tuning of electroweak symmetry breaking. All gaugino, squark and slepton masses are determined by one parameter -- the supersymmetry breaking scale. The characteristic features are: negative and non-universal squark and slepton masses squared at the unification scale, non-universal gaugino masses, and sizable soft-trilinear couplings. In this scenario, all soft supersymmetry breaking parameters at the unification scale can be smaller than 400 GeV and all the superpartners can be lighter than 400 GeV and still satisfy all the limits from direct searches for superpartners and also the limit on the Higgs mass. The lightest supersymmetric particle is gravitino or a sizable mixture of bino, wino and higgsino. We also consider a possible contributions from additional messengers in vector-like representations, and a contribution from gravity mediation, which is estimated to be comparable.

hep-ph↗
arXiv2006

Radiatively Generated Maximal Mixing Scenario for the Higgs Mass and the Least Fine Tuned Minimal Supersymmetric Standard Model

We argue that given the experimental constraints on the Higgs mass the least fine tuned parameter space of minimal supersymmetric standard model is with negative stop masses squared at the grand unification scale. While stop mass squared is typically driven to positive values at the weak scale, the contribution to the Higgs mass squared parameter from the running can be arbitrarily small, which reduces fine tuning of electroweak symmetry breaking. At the same time the stop mixing is necessarily enhanced and the maximal mixing scenario for the Higgs mass can be generated radiatively even when starting with negligible mixing at the unification scale. This highly alleviates constraints on possible models for supersymmetry breaking in which fine tuning is absent.

hep-ph↗
arXiv2005

Consistency of LEP $Z+b$-jets excess with an {\boldmath $h\to aa$} Decay Scenario and Low-Fine-Tuning NMSSM Models

We examine the LEP limits for the $Zh\to Z+b$'s final state and find that the excess of observed events for $\mh\sim 100\gev$ correlates well with there being an $\mh\sim 100\gev$ Higgs boson with SM-like $ZZh$ coupling that decays partly via $h\to b\anti b+\tauptaum$ [with $\br(h\to b\anti b)\sim 0.08$] but dominantly via $h\to aa$ [with $\br(h\to aa)\sim 0.9$], where $\ma<2\mb$ so that $a\to \tauptaum$ (or light quarks and gluons) decays are dominant. Scenarios of precisely this type arise in the Next-to-Minimal Supersymmetric Model for parameter choices yielding the lowest possible fine-tuning.

hep-ph↗
arXiv2005

Bi-large Neutrino Mixing and CP violation in an SO(10) SUSY GUT for Fermion Masses

We construct a simple SO(10) SUSY GUT with $D_3$ family symmetry and low energy R parity. The model describes fermion mass matrices with 14 parameters and gives excellent fits to 20 observable masses and mixing angles in both quark and lepton sectors, giving 6 predictions. Bi-large neutrino mixing is obtained with hierarchical quark and lepton Yukawa matrices; thus avoiding the possibility of large lepton flavor violation. The model naturally predicts small 1-3 neutrino mixing, $\sin θ_{13} \simeq 0.05$, and a CP violating phase $δ$ close to $π/2$. Among other interesting predictions is a tiny effective Majorana mass for neutrinoless double-beta decay. Leptogenesis is also possible with the decay of the lightest right-handed neutrino giving an acceptable CP violating asymmetry $ε_1$ of order $10^{-6}$, {\em and with the correct sign for the resultant baryon asymmetry}. We also show how similar models with the non-abelian symmetry groups SU(2) or $D_4$, instead of $D_3$, can be constructed.

hep-ph↗
arXiv2004

Neutrino Masses and Mixing, Quark-lepton Symmetry and Strong Right-handed Neutrino Hierarchy

Assuming the same form of all mass matrices as motivated by quark-lepton symmetry, we discuss conditions under which bi-large mixing in the lepton sector can be obtained with a minimal amount of fine tuning requirements for possible models. We assume hierarchical mass matrices, dominated by the 3-3 element, with off-diagonal elements much smaller than the larger neighboring diagonal element. Characteristic features of this scenario are strong hierarchy in masses of right-handed neutrinos, and comparable contributions of both lighter right-handed neutrinos to the resulting left-handed neutrino Majorana mass matrix. Due to obvious quark lepton symmetry, this approach can be embedded into grand unified theories. The mass of the lightest neutrino does not depend on details of a model in the leading order. The right-handed neutrino scale can be identified with the GUT scale in which case the mass of the lightest neutrino is given as (m_{top}^2/M_{GUT}) |U_{τ1}|^2.

hep-ph↗