arXiv subjects

Ulrich Ellwanger

Publications and source records attributed to Ulrich Ellwanger.

At least 55 records · Page 3Linked to original sources

arXiv2009

Phenomenological Aspects of the Next-to-Minimal Supersymmetric Standard Model

The motivations for the NMSSM are reviewed, and possible unconventional signals for Higgs and sparticle production at the LHC are discussed. In the presence of a light pseudoscalar, the SM-like Higgs scalar can decay dominantly into a 4-tau final state. In the fully constrained NMSSM with mSUGRA-like soft SUSY breaking terms, the correct dark matter relic density is obtained for a singlino-like LSP which modifies considerably all sparticle decay chains.

hep-ph↗

arXiv2009

Bottomonium spectroscopy with mixing of eta_b states and a light CP-odd Higgs

The mass of the eta_b(1S), measured recently by BABAR, is significantly lower than expected from QCD predictions for the Upsilon(1S) - eta_b(1S) hyperfine splitting. We suggest that the observed eta_b(1S) mass is shifted downwards due to a mixing with a CP-odd Higgs scalar A with a mass m_A in the range 9.4 - 10.5 GeV compatible with LEP, CLEO and BABAR constraints. We determine the resulting predictions for the spectrum of the eta_b(nS) - A system and the branching ratios into tau^+ tau^- as functions of m_A.

hep-ph↗

arXiv2009

CDF Multi-Muon Events and Singlet Extensions of the MSSM

We discuss a generalization of the minimal supersymmetric extension of the Standard Model in the form of three additional singlet superfields, which would explain the essential features of the CDF multi-muon events presented recently: a large production cross section of ~ 100 pb originates from the production of a CP-odd scalar A with a mass in the 70 - 80 GeV range and a large value of tan(beta) ~ 40. The CP-odd scalar A decays dominantly into CP-odd and CP-even scalars a_1 and h_1, which generate decay cascades h_1 -> 2 h_2 -> 4 a_2 -> 8 tau-leptons, and a_1 -> h_1 a_2 with h_1 decaying as above. The decay a_2 -> tau+ tau- is slow, leading to a lifetime of O(20) ps. The phenomenology of the model differs from similar scenarios presented before in that one of the two cascades leads to 10 instead of 8 tau-leptons, and additional production processes like associate A production with b b-bar pairs are relevant.

hep-ph↗

arXiv2009

Radiative Upsilon decays and a light pseudoscalar Higgs in the NMSSM

We study possible effects of a light CP-odd Higgs boson on radiative Upsilon decays in the Next-to-Minimal Supersymmetric Standard Model. Recent constraints from CLEO on radiative Upsilon(1S) decays are translated into constraints on the parameter space of CP-odd Higgs boson masses and couplings, and compared to constraints from B physics and the muon anomalous magnetic moment. Possible Higgs - eta_b(nS) mixing effects are discussed, notably in the light of the recent measurement of the eta_b(1S) mass by Babar: The somewhat large Upsilon(1S) - eta_b(1S) hyperfine splitting could easily be explained by the presence of a CP-odd Higgs boson with a mass in the range 9.4 - 10.5 GeV. Then, tests of lepton universality in inclusive radiative Upsilon decays can provide a visible signal in forthcoming experimental data.

hep-ph↗

arXiv2008

The constrained NMSSM: mSUGRA and GMSB

We review different constrained versions of the NMSSM: the fully constrained cNMSSM with universal boundary conditions for gauginos and all soft scalar masses and trilinear couplings, and the NMSSM with soft terms from Gauge Mediated Supersymmetry Breaking. Regarding the fully constrained cNMSSM, after imposing LEP constraints and the correct dark matter relic density, one single parameter is sufficient to describe the entire Higgs and sparticle spectrum of the model, which then contains always a singlino LSP. The NMSSM with soft terms from GMSB is phenomenologically viable if (and only if) the singlet is allowed to couple directly to the messenger sector; then various ranges in parameter space satisfy constraints from colliders and precision observables. Motivations for and phenomenological features of extra U(1)' gauge symmetries are briefly reviewed.

hep-ph↗

arXiv2008

Constraints from the Muon g-2 on the Parameter Space of the NMSSM

We generalize the computation of supersymmetric contributions to the muon anomalous magnetic moment (g-2)_mu to the NMSSM. In the presence of a light CP-odd Higgs scalar, these can differ considerably from the MSSM. We discuss the amount of these contributions in regions of the parameter space of the general NMSSM compatible with constraints from B physics. In the mSUGRA-like cNMSSM, constraints from (g-2)_mu prefer regions in parameter space corresponding to a low SUSY breaking scale.

hep-ph↗

arXiv2007

Updated Constraints from B Physics on the MSSM and the NMSSM

We update constraints from B physics observables on the parameters of the MSSM and the NMSSM, combining them with LEP constraints. Presently available SM and Susy radiative corrections are included in the calculations, which will be made public in the form of a Fortran code. Results for the tan(beta) and M_{H^+} dependence of b -> s gamma are presented, as well as constraints on the NMSSM specific case of a light CP odd Higgs scalar. We find that the latter are essentially due to B_s -> mu^+ mu^-, but they do not exclude this possibility.

hep-ph↗

arXiv2007

The upper bound on the lightest Higgs mass in the NMSSM revisited

We update the upper bound on the lightest CP even Higgs mass in the NMSSM, which is given as a function of tan(beta) and lambda. We include the available one and two loop corrections to the NMSSM Higgs masses, and constraints from the absence of Landau singularities below the GUT scale as well as from the stability of the NMSSM Higgs potential. For m_top varying between 171.4 and 178 GeV, squark masses of 1 TeV and maximal mixing the upper bound is assumed near tan(beta) ~ 2 and varies between 139.9 and 141.4 GeV.

hep-ph↗

arXiv2007

NMHDECAY 2.0: An updated program for Sparticle masses, Higgs masses, couplings and decay widths in the NMSSM

We describe the the improved properties of the NMHDECAY program, that is designed to compute Higgs and sparticle masses and Higgs decay widths in the NMSSM. In the version 2.0, Higgs decays into squarks and sleptons are included, accompagnied by a calculation of the squark, gluino and slepton spectrum and tests against constraints from LEP and the Tevatron. Further radiative corrections are included in the Higgs mass calculation. A link to MicrOMEGAs allows to compute the dark matter relic density, and a rough (lowest order) calculation of the BR(s -> b gamma) is performed.

hep-ph↗

arXiv2006

NMSPEC: A Fortran code for the sparticle and Higgs masses in the NMSSM with GUT scale boundary conditions

NMSPEC is a Fortran code that computes the sparticle and Higgs masses, as well as Higgs decay widths and couplings in the NMSSM, with soft SUSY breaking terms specified at MGUT. Exceptions are the soft singlet mass m_s^2 and the singlet self coupling kappa, that are both determined in terms of the other parameters through the minimization equations of the Higgs potential. We present a first analysis of the NMSSM parameter space with universal SUSY breaking terms at MGUT -- except for m_s and A_kappa -- that passes present experimental constraints on sparticle and Higgs masses. We discuss in some detail a region in parameter space where a SM-like Higgs boson decays dominantly into two CP odd singlet-like Higgs states.

hep-ph↗

arXiv2005

Brane Universes and the Cosmological Constant

The cosmological constant problem and brane universes are reviewed briefly. We discuss how the cosmological constant problem manifests itself in various scenarios for brane universes. We review attempts - and their difficulties - that aim at a solution of the cosmological constant problem.

hep-th↗

arXiv2005

Yukawa Induced Radiative Corrections to the Lightest Higgs Boson Mass in the NMSSM

We compute the leading logarithmic radiative corrections to the lightest Higgs mass in the NMSSM involving the electroweak gauge couplings and in the NMSSM specific Yukawa couplings lambda and kappa (including all mixed combinations), which are induced by chargino, neutralino and Higgs boson loops. The effect of the NMSSM specific Yukawa couplings lambda and kappa is to increase the upper bound on the lightest Higgs mass by up to ~2 GeV, but they can also decrease the lightest Higgs mass by up to ~-20 GeV.

hep-ph↗

arXiv2005

Difficult Scenarios for NMSSM Higgs Discovery at the LHC

We identify scenarios not ruled out by LEP data in which NMSSM Higgs detection at the LHC will be particularly challenging. We first review the `no-lose' theorem for Higgs discovery at the LHC that applies if Higgs bosons do not decay to other Higgs bosons - namely, with L=300 fb^-1, there is always one or more `standard' Higgs detection channel with at least a 5 sigma signal. However, we provide examples of no-Higgs-to-Higgs cases for which all the standard signals are no larger than 7 sigma implying that if the available L is smaller or the simulations performed by ATLAS and CMS turn out to be overly optimistic, all standard Higgs signals could fall below 5 sigma even in the no-Higgs-to-Higgs part of NMSSM parameter space. In the vast bulk of NMSSM parameter space, there will be Higgs-to-Higgs decays. We show that when such decays are present it is possible for all the standard detection channels to have very small significance. In most such cases, the only strongly produced Higgs boson is one with fairly SM-like couplings that decays to two lighter Higgs bosons (either a pair of the lightest CP-even Higgs bosons, or, in the largest part of parameter space, a pair of the lightest CP-odd Higgs bosons). A number of representative bench-mark scenarios of this type are delineated in detail and implications for Higgs discovery at various colliders are discussed.

hep-ph↗

arXiv2005

NMHDECAY: A Fortran Code for the Higgs Masses, Couplings and Decay Widths in the NMSSM

The Fortran code NMHDECAY computes the masses, couplings and decay widths of all Higgs bosons of the NMSSM in terms of its parameters at the electroweak (SUSY breaking) scale: the Yukawa couplings lambda and kappa, the soft trilinear terms A_lambda and A_kappa, and tan(beta) and mu_eff = lambda* . The computation of the spectrum includes leading two loop terms, electroweak corrections and propagator corrections. The computation of the decay widths is carried out as in HDECAY, but (for the moment) without three body decays. Each point in parameter space is checked against negative Higgs bosons searches at LEP, including unconventional channels relevant for the NMSSM. One version of the program uses generalized SLHA conventions for input and output.

hep-ph↗

arXiv2003

Towards a No-Lose Theorem for NMSSM Higgs Discovery at the LHC

We scan the parameter space of the NMSSM for the observability of a Higgs boson at the LHC with $300 {\rm fb}^{-1}$ integrated luminosity per detector, taking the present LEP constraints into account. We focus on the regions of parameter space for which none of the usually considered LHC detection modes are viable due to the fact that the only light non-singlet (and, therefore, potentially visible) Higgs boson, $h$, decays mainly to two CP-odd light Higgs bosons, $h\to a a$. We simulate the $WW\to h \to aa$ detection mode. We find that this signal may be detectable at the LHC as a signal/background $\sim 600/600$ bump in the tail of a rapidly falling mass distribution. If further study gives us confidence that the shape of the background tail is predictable, then we can conclude that NMSSM Higgs detection at the LHC will be possible throughout all of parameter space by combining this signal with the usual detection modes previously simulated by ATLAS and CMS. We also show that this $WW\to h\to aa$ signal will be highly visible at the LC due to its cleaner environment and high luminosity. We present a study of the production modes and decay channels of interest at the LC.

hep-ph↗

arXiv2000

Brane cosmological evolution in a bulk with cosmological constant

We consider the cosmology of a ``3-brane universe'' in a five dimensional (bulk) space-time with a cosmological constant. We show that Einstein's equations admit a first integral, analogous to the first Friedmann equation, which governs the evolution of the metric in the brane, whatever the time evolution of the metric along the fifth dimension. We thus obtain the cosmological evolution in the brane for any equation of state describing the matter in the brane, without needing the dependence of the metric on the fifth dimension. In the particular case $p = w ρ$, $(w = constant)$, we give explicit expressions for the time evolution of the brane scale factor, which show that standard cosmological evolution can be obtained (after an early non conventional phase) in a scenario à la Randall and Sundrum, where a brane tension compensates the bulk cosmological constant. We also show that a tiny deviation from exact compensation leads to an effective cosmological constant at late time. Moreover, when the metric along the fifth dimension is static, we are able to extend the solution found on the brane to the whole spacetime.

hep-th↗

arXiv1998

Field Strength Correlator and an Infrared Fixed Point of the Wilsonian Exact Renormalization Group Equations

The correlator of two field strengths is computed from an effective action for Yang Mills theories, which contains both gluons and an auxiliary antisymmetric tensor field for the field strength as local variables. This action allows to relate explicitly many different approaches to confinement, and is computed using Wilsonian renormalization group equations with the bare Yang Mills action as starting point. Due to the inclusion of a higher dimensional operator in the ghost sector the running gauge coupling becomes vanishingly small at a critical scale k_c, and the resulting low energy action resembles the action of a confining string theory proposed by Polyakov.

hep-ph↗

arXiv1997

Confinement, Monopoles and Wilsonian Effective Action

An effective low energy action for Yang-Mills theories is proposed, which invokes an additional auxiliary field $H_{μν}$ for the field strength $F_{μν}$. For a particular relation between the parameters of this action a gluon propagator with a $1/p^4$ behaviour for $p^2 \to 0$ in the Landau gauge is obtained. The abelian subsector of this action admits a duality transformation, where the dual action contains a Goldstone boson $φ$ as the dual of $H_{μν}$, and corresponds to an abelian Higgs model in the broken phase describing the condensation of magnetic charges. The Wilsonian renormalization group equations for the parameters of the original action are integrated in some approximation, and we find that the relation among the parameters associated with confinement appears as an infrared attractive fixed point.

hep-ph↗