Large Tan Beta Research Articles

Investigation of (g-2)_{mu } anomaly in the mu -specific 2HDM with vector like leptons and the phenomenological implications

The anomalous magnetic moment of muons has been a long-standing problem in SM. The current deviation of experimental value of the (g-2)_{mu } from the standard model prediction is exactly 4.2sigma . Two Higgs Doublet Models can accommodate this discrepancy but such type of model naturally generate flavor changing neutral current(FCNC). To prevent this it was postulated that 2HDM without FCNC required that all fermions of a given charge couple to the same Higgs boson but the rule breaks in Muon Specific Two Higgs Doublet Model where all fermions except muon couple to one Higgs doublet and muon with the other Higgs doublet. The muon specific 2HDM provides an explanation for muon anomaly for extremely large tan beta with a particular value of m_{12}^2. As a result, the parameter space of m_{12}^2 drastically decreased for the muon anomaly solution. To evade the limitation of this model we have extended this model with a vector like lepton generation which could explain the muon anomaly at low tan beta value with a heavy pseudo scalar Higgs boson under the shadow of current experimental and theoretical constraints. Moreover, with the help of the cut based analysis and multivariate analysis methods, we have also attempted to shed some light on the potential experimental signature of vector lepton decay to the heavy Higgs boson in the LHC experiment. We have showed that a multivariate analysis can increase the vector like leptons signal significance even in the high VLL mass and low tan beta region than that of a cut based analysis.

The CMSSM survives Planck, the LHC, LUX-ZEPLIN, Fermi-LAT, H.E.S.S. and IceCube

We revisit the viability of the CMSSM, searching for regions of parameter space that yield a neutralino dark matter density compatible with Planck measurements, as well as LHC constraints including sparticle searches and the mass of the Higgs boson, recent direct limits on spin-independent and -dependent dark matter scattering from the LUX-ZEPLIN (LZ) experiment, the indirect constraints from Fermi-LAT and H.E.S.S. on dark matter annihilations to photons in dwarf spheroidal galaxies and the Galactic Centre, and the IceCube limits on muons from annihilations to neutrinos in the Sun. For representative values of tan beta and A_0 we map in detail the Planck-compatible strips in CMSSM parameter planes, which exhibit multiple distinctive features for large tan beta , A_0 = 0 and mu > 0, and identify portions of the strips that survive all the phenomenological constraints. We find that the most powerful constraint is that from m_h, followed by the LZ limit on spin-independent scattering, whereas sparticle searches at the LHC and indirect dark matter searches are less restrictive. Most of the surviving CMSSM parameter space features a Higgsino-like dark matter particle with a mass sim 1000{-}1100 GeV, which could best be probed with future direct searches for dark matter scattering.

Fine-tuning in the 2HDM

The Two-Higgs Doublet Model (2HDM) is one of the most popular and natural extensions of the Higgs sector; but it has two potential fine-tuning problems, related to the electroweak (EW) breaking and the requirement of alignment with the SM Higgs boson. We have quantified the fine-tunings obtaining analytical expressions, both in terms of the initial 2HDM parameters and the physical ones (masses, mixing angles, etc.). We also provide simple approximate expressions. We have taken into account that the fine-tunings are not independent and removed the “double counting” by projecting the variations of the alignment onto the constant-v^2 hypersurface. The EW and the alignment fine-tunings become severe in different, even opposite, regions of the parameter space, namely in the regimes of large and small extra-Higgs masses, respectively; emerging an intermediate region, 500~{textrm{GeV}} {mathop {{}_sim }limits ^{<}}{m_H, m_A, m_{H^pm }} {mathop {{}_sim }limits ^{<}}700~{textrm{GeV}}, where both are acceptably small. We also discuss a remarkable trend that is not obvious at first glance. Namely, for large tan beta both the EW and the alignment fine-tunings become mitigated. In consequence, the 2HDM becomes quite natural for tan beta ge {mathcal {O}} (10), even if m_H, m_A, m_{H^pm } are as large as 1500 GeV. We explain why this is not the case for the 2HDM stemming from supersymmetry. We have illustrated all these trends by numerically analyzing several representative scenarios.

The light MSSM Higgs boson mass for large tan beta and complex input parameters

We discuss various improvements of the prediction for the light MSSM Higgs boson mass in the hybrid framework of the public code texttt {FeynHiggs}, which combines fixed-order and effective field theory results. First, we discuss the resummation of logarithmic contributions proportional to the bottom-Yukawa coupling including two-loop Delta _b resummation. For large tan beta , these improvements can lead to large upward shifts of the Higgs mass compared to the existing fixed-order calculations. Second, we improve the implemented EFT calculation by fully taking into account the effect of mathcal{CP}-violating phases. As a third improvement, we discuss the inclusion of partial hbox {N}^3LL resummation. The presented improvements will be implemented into texttt {FeynHiggs}.

Mass-degenerate Higgs bosons near 125\xa0GeV in the NMSSM under current experimental constraints

The observed Higgs signal at the Large Hadron Collider (LHC) may be derived from the two mass-degenerate resonances. We investigate this scenario in the Next-to-Minimal Supersymmetric Standard Model (NMSSM) in which both the two lightest CP-even Higgs bosons have masses around 125 GeV. We perform a comprehensive scan over the parameters in the NMSSM considering the current experimental constraints, especially the constraints from dark matter direct detection. The surviving samples are featured with relatively small mu and large tan beta . The samples with large deviation of double ratios have large mixing between doublet field and singlet field.

Vacuum stability of asymptotically safe two Higgs doublet models

We study different types of Two Higgs Doublet Models (2HDMs) under the assumption that all quartic couplings’ beta functions vanish simultaneously at the Planck scale. The Standard Model seems to display this property almost accidentally, because the Higgs boson mass is close to 125 GeV. This also ties closely into the question of whether the theory is stable or metastable. We investigate if such “fixed points” can exist in various {mathbb {Z}}_2-symmetric 2HDM subclasses, and if the theories that meet these conditions are phenomenologically viable, as well as vacuum stable. We find that the fixed point condition drastically reduces the parameter space of 2HDM theories, but can be met. Fixed points can only exist in type II and type Y models, in regions of large tanbeta , and they are only compatible with all existing experimental bounds if the {mathbb {Z}}_2-symmetry is at least softly broken, with a soft breaking parameter of at least M_{12}> 70 GeV (380 GeV) for type Y (type II) models. The allowed region falls into the alignment limit, with the mixing angle combination |alpha - beta | approx frac{pi }{2}. While there are both vacuum-stable and vacuum-unstable solutions, only the vacuum-unstable ones really agree with Standard-Model-like CP-even Higgs boson mass values of 125 GeV. The vacuum-stable solutions favour slightly higher values. While scenarios of asymptotically safe 2HDM exist, they cannot improve over the Standard Model regarding the question of vacuum stability.

Naturalness, b → sγ, and SUSY heavy Higgses

We explore naturalness constraints on the masses of the heavy Higgs bosons H^0, H^+/-, and A^0 in supersymmetric theories. We show that, in any extension of MSSM which accommodates the 125 GeV Higgs at the tree level, one can derive an upper bound on the SUSY Higgs masses from naturalness considerations. As is well-known for the MSSM, these bounds become weak at large tan beta. However, we show that measurements of b to s gamma together with naturalness arguments lead to an upper bound on tan beta, strengthening the naturalness case for heavy Higgs states near the TeV scale. The precise bound depends somewhat on the SUSY mediation scale: allowing a factor of 10 tuning in the stop sector, the measured rate of b to s gamma implies tan beta < 30 for running down from 10 TeV but tan beta < 4 for mediation at or above 100 TeV, placing m_A near the TeV scale for natural EWSB. Because the signatures of heavy Higgs bosons at colliders are less susceptible to being "hidden" than standard superpartner signatures, there is a strong motivation to make heavy Higgs searches a key part of the LHC's search for naturalness. In an appendix we comment on how the Goldstone boson equivalence theorem links the rates for H to hh and H to ZZ signatures.

Revisiting the Higgs mass and dark matter in the CMSSM

Taking into account the available accelerator and astrophysical constraints, the mass of the lightest neutral Higgs boson h in the minimal supersymmetric extension of the Standard Model with universal soft supersymmetry-breaking masses (CMSSM) has been estimated to lie between 114 and ~ 130 GeV. Recent data from ATLAS and CMS hint that m_h ~ 125 GeV, though m_h ~ 119 GeV may still be a possibility. Here we study the consequences for the parameters of the CMSSM and direct dark matter detection if the Higgs hint is confirmed, focusing on the strips in the (m_1/2, m_0) planes for different tan beta and A_0 where the relic density of the lightest neutralino chi falls within the range of the cosmological cold dark matter density allowed by WMAP and other experiments. We find that if m_h ~ 125 GeV focus-point strips would be disfavoured, as would the low-tan beta stau-chi and stop -chi coannihilation strips, whereas the stau-chi coannihilation strip at large tan beta and A_0 > 0 would be favoured, together with its extension to a funnel where rapid annihilation via direct-channel H/A poles dominates. On the other hand, if m_h ~ 119 GeV more options would be open. We give parametrizations of WMAP strips with large tan beta and fixed A_0/m_0 > 0 that include portions compatible with m_h = 125 GeV, and present predictions for spin-independent elastic dark matter scattering along these strips. These are generally low for models compatible with m_h = 125 GeV, whereas the XENON100 experiment already excludes some portions of strips where m_h is smaller.

Relaxing the Higgs mass bound in singlet extensions of the MSSM

We show that the upper bound on the lightest Higgs mass in the MSSM is relaxed by introducing a singlet which couples to the Higgs fields, even at a large tan beta region, preferable for explaining the muon anomalous magnetic moment. In the models of a singlet extension, it is known that the upper bound is relaxed by a tree-level contribution, especially at small tan beta region. For large tan beta, however, the requirement for the perturbativity on the singlet-Higgs coupling up to the GUT scale prevents the lightest Higgs from obtaining a large tree-level mass. We construct an explicit UV complete model which allows large singlet-Higgs coupling at low energy without disturbing the perturbativity. The UV completion can be applied for any singlet extension of the MSSM. Moreover, we point out that the radiative correction from the singlet-Higgs coupling becomes dominant, and the lightest Higgs mass can be easily as heavy as 130 GeV if this coupling is large enough even for large tan beta.

Higgs mass and muon anomalous magnetic moment in supersymmetric models with vectorlike matters

We study the muon anomalous magnetic moment (muon g-2) and the Higgs boson mass in a simple extension of the minimal supersymmetric (SUSY) Standard Model with extra vector-like matters, in the frameworks of gauge mediated SUSY breaking (GMSB) models and gravity mediation (mSUGRA) models. It is shown that the deviation of the muon g-2 and a relatively heavy Higgs boson can be simultaneously explained in large tan-beta region. (i) In GMSB models, the Higgs mass can be more than 135 GeV (130 GeV) in the region where muon g-2 is consistent with the experimental value at the 2 sigma (1 sigma) level, while maintaining the perturbative coupling unification. (ii) In the case of mSUGRA models with universal soft masses, the Higgs mass can be as large as about 130 GeV when muon g-2 is consistent with the experimental value at the 2 sigma level. In both cases, the Higgs mass can be above 140 GeV if the g-2 constraint is not imposed.

Minimal flavor violation and the scale of supersymmetry breaking

In this paper we explore the constraints from B-physics observables in SUSY models of Minimal Flavor Violation, in the large tan beta regime, for both low and high scale supersymmetry breaking scenarios. We find that the rare B-decays b -> s gamma and B_s -> mu+ mu- can be quite sensitive to the scale M at which supersymmetry breaking is communicated to the visible sector. In the case of high scale supersymmetry breaking, we show that the additional gluino contribution to the b -> s gamma and B_s -> mu+ mu- rare decay rates can be significant for large tan beta, mu and M_3. The constraints on B_u -> tau nu are relatively insensitive to the precise scale of M. We also consider the additional constraints from the present direct Higgs searches at the Tevatron in the inclusive H/A -> tau tau channel, and the latest CDMS direct dark matter detection experiments. We find that altogether the constraints from B-physics, Higgs physics and direct dark matter searches can be extremely powerful in probing regions of SUSY parameter space for low M_A and large tan beta, leading to a preference for models with a lightest CP-even Higgs mass close to the current experimental limit. We find interesting regions of parameter space that satisfy all constraints and can be probed by Higgs searches at the Tevatron and the LHC and by direct dark matter searches in the near future.

Search for Neutral Higgs Bosons at Hightanβin theb(h/H/A)→bτ+τ−Channel

The first search in pp[over ] collisions at sqrt[s]=1.96 TeV for the production of neutral Higgs bosons in association with bottom quarks and decaying in two tau leptons is presented. The cross section for this process is enhanced in many extensions of the standard model, such as its minimal supersymmetric extension (MSSM) at large tanbeta. The data, corresponding to an integrated luminosity of 328 pb;{-1}, were collected with the D0 detector at the Fermilab Tevatron Collider. An upper limit is set on the production cross section of neutral Higgs bosons in the mass range of 90 to 150 GeV, and this limit is used to exclude part of the MSSM parameter space.

Anomaly ofZbb̄ coupling revisited in MSSM and NMSSM

The Zbb coupling determined from the Z-pole measurements at LEP/SLD shows an about 3-sigma deviation from the SM prediction, which would signal the presence of new physics in association with the Zbb coupling. In this work we give a comprehensive study for the full one-loop supersymmetric effects on the Zbb coupling in both the MSSM and the NMSSM by considering all current constraints which are from the precision electroweak measurements, the direct search for sparticles and Higgs bosons, the stability of Higgs potential, the dark matter relic density, and the muon g-2 measurement. We analyze the characters of each type of the corrections and search for the SUSY parameter regions where the corrections could be sizable. We find that the sizable corrections may come from the Higgs sector with light m_A and large tan-beta, which can reach -2% and -6% for rho_b and sin^2 \theta_{eff}^b,respectively. However, such sizable negative corrections are just opposite to what needed to solve the anomaly. We also scan over the allowed parameter space and investigate to what extent supersymmetry can narrow the discrepancy. We find that under all current constraints, the supersymmetric effects are quite restrained and cannot significantly ameliorate the anomaly of Zbb coupling. Compared with \chi^2/dof = 9.62/2 in the SM, the MSSM and NMSSM can only improve it to \chi^2/dof = 8.77/2 in the allowed parameter space. Therefore, if the anomaly of Zbb coupling is not a statistical or systematic problem, it would suggest new physics beyond the MSSM or NMSSM.

A simple model of low-scale direct gauge mediation

We construct a calculable model of low-energy direct gauge mediation making use of the metastable supersymmetry breaking vacua recently discovered by Intriligator, Seiberg and Shih. The standard model gauge group is a subgroup of the global symmetries of the SUSY breaking sector and messengers play an essential role in dynamical SUSY breaking: they are composites of a confining gauge theory, and the holomorphic scalar messenger mass appears as a consequence of the confining dynamics. The SUSY breaking scale is around 100 TeV nevertheless the model is calculable. The minimal non-renormalizable coupling of the Higgs to the DSB sector leads in a simple way to a mu-term, while the B-term arises at two-loop order resulting in a moderately large tan beta. A novel feature of this class of models is that some particles from the dynamical SUSY breaking sector may be accessible at the LHC.

Implications of Direct Dark Matter Constraints for Minimal Supersymmetric Standard Model Higgs Boson Searches at the Tevatron

In regions of large tanbeta and small mAlpha, searches for heavy neutral minimal supersymmetric standard model (MSSM) Higgs bosons at the Tevatron are promising. At the same time, rates in direct dark matter experiments, such as CDMS, are enhanced in the case of large tanbeta and small mAlpha. As a result, there is a natural interplay between the heavy, neutral Higgs searches at the Tevatron and the region of parameter space explored by CDMS. We show that if the lightest neutralino makes up the dark matter of our universe, current limits from CDMS strongly constrain the prospects of heavy, neutral MSSM Higgs discovery at the Tevatron unless |mu| greater or approximately 400 GeV. The limits of CDMS projected for 2007 will increase this constraint to |mu| greater or approximately 800 GeV. If CDMS does observe neutralinos in the near future, however, it will make the discovery of Higgs bosons at the Tevatron far more likely.

SUSY phenomenology of KKLT flux compactifications

We study SUSY phenomenology of the KKLT (Kachru-Kallosh-Linde-Trivedi) scenario of string theory compactifications with fluxes. This setup leads to a specific pattern of soft masses and distinct phenomenological properties. In particular, it avoids the cosmological gravitino/moduli problems. Remarkably, the model allows for the correct abundance of SUSY dark matter consistently with all experimental constraints including the bound on the Higgs mass, b-->s gamma, etc. This occurs for both small and large tan beta, and requires the SUSY spectrum above 1 TeV.

Large 2HDM(II) one-loop corrections in leptonic tau decays

The one-loop contributions to the branching ratios for leptonic tau decays are calculated in the CP conserving 2HDM(II). We found that these one-loop contributions, involving both neutral and charged Higgs bosons, dominate over the tree-level H^+ exchange, the latter one being totally negligible for the decay into electron. The analysis is focused on large tanbeta enhanced contributions to the considered branching ratios. We derive a simple analytical expression for the one-loop contribution which holds in this case. We show that the leptonic branching ratios of tau are complementary to the Higgsstrahlung processes for h(H) and have a large potential on constraining parameters of the model. In this work we provide upper limits on Yukawa couplings for both light h and light A scenarios and we derive new lower limit on mass of M_{H^+} as a function of tanbeta, which differs significantly from what was considered as standard constraint based on the tree-level H^{+} exchange only. Interestingly we obtain also an upper limit on M_{H^+}. For a SM-like h scenario, with heavy and degenerate additional Higgs bosons, one-loop corrections disappear.

Search for Neutral Supersymmetric Higgs Bosons in Multijet Events ats=1.96 TeV

We have performed a search for neutral Higgs bosons produced in association with bottom quarks in pp collisions, using 260 pb-1 of data collected with the D0 detector in Run II of the Fermilab Tevatron Collider. The cross sections for these processes are enhanced in many extensions of the standard model (SM), such as in its minimal supersymmetric extension at large tanbeta. The results of our analysis agree with expectations from the SM, and we use our measurements to set upper limits on the production of neutral Higgs bosons in the mass range of 90 to 150 GeV.

Some novel contributions to radiativeBdecays in supersymmetry withoutRparity

We present a systematic analysis at the leading log order of the influence of combination of bilinear and trilinear R-parity violating couplings on the decay b-->s gamma. Such contributions have never been explored in the context of this decay. We show that influence of charged-slepton-Higgs mixing mediated loops can dominate the SM and MSSM contributions and hence can provide strong bounds on the combination of bilinear-trilinear R-parity violating couplings. Such contributions are also enhanced by large tan beta. With substantially extended basis of operators (28 operators), we provide illustrative analytical formulae of the major contributions to complement our complete numerical results which demonstrate the importance of QCD running effects.

Measurement of the H/A $\rightarrow\tau\tau$ cross sectionand possible constraints on tan $\beta$

The achievable precision of the cross section times branching ratio measurement from the event rates is estimated for the MSSM H/A -> tau tau decay in the associated production process gg -> b bbar H/A at large tan beta in CMS. This work demonstrates that the above production and decay process exhibit a large sensitivity to tan beta and thus add as a significant observable to a global fit of the SUSY parameters. To illustrate this potential an example is given concerning the achievable tan beta determination accuracy that could be reached from the event rates and for a given set of SUSY parameters and uncertainties.