Tan Beta Research Articles

Relations between basis sets of fields in the renormalization procedure

It seems that the literature suggests to go in two opposing directions simultaneously. On the one hand, many papers construct basis-independent quantities, since exactly these quantities appear in the expressions for observables. This means that the mixing angles such as tan beta in the generic Two Higgs Doublet Model must drop out when calculating anything physical. On the other hand, there are many attempts to renormalize such mixing angles – this is in the opposite direction to basis-independence. This basis-dependent approach seems to bring gauge-dependence and singular behaviour, both of which are required to be absent in mixing renormalization. Most importantly, mixing angle counterterms single out a preferred basis and further basis rotations lead to inconsistencies. In contrast, we argue that the bare mixing angles should be identified with the renormalized ones – this is the basis-independent approach – such that all the mixing renormalization requirements are fulfilled in a trivial and consistent manner.

Full NLO QCD predictions for Higgs-pair production in the 2-Higgs-doublet model

After the discovery of the Higgs boson in 2012 at the CERN Large Hadron Collider (LHC), the study of its properties still leaves room for an extended Higgs sector with more than one Higgs boson. 2-Higgs doublet models (2HDMs) are well-motivated extensions of the Standard Model (SM) with five physical Higgs bosons: two CP-even states h and H, one CP-odd state A, and two charged states H^pm _{}. In this letter, we present the calculation of the full next-to-leading order (NLO) QCD corrections to hH and AA production at the LHC in the 2HDM at small values of the ratio of the vacuum expectation values, tan beta , including the exact top-mass dependence everywhere in the calculation. Using techniques applied in the NLO QCD SM Higgs pair production calculation, we present results for the total cross section as well as for the Higgs-pair-mass distribution at the LHC. We also provide the top-quark scale and scheme uncertainties which are found to be sizeable.

Search for dark matter produced in association with a single top quark and an energetic W boson in sqrt{s}= 13 TeV pp collisions with the ATLAS detector

This paper presents a search for dark matter, chi , using events with a single top quark and an energetic W boson. The analysis is based on proton–proton collision data collected with the ATLAS experiment at sqrt{s}= 13 TeV during LHC Run 2 (2015–2018), corresponding to an integrated luminosity of 139 fb^{-1}. The search considers final states with zero or one charged lepton (electron or muon), at least one b-jet and large missing transverse momentum. In addition, a result from a previous search considering two-charged-lepton final states is included in the interpretation of the results. The data are found to be in good agreement with the Standard Model predictions and the results are interpreted in terms of 95% confidence-level exclusion limits in the context of a class of dark matter models involving an extended two-Higgs-doublet sector together with a pseudoscalar mediator particle. The search is particularly sensitive to on-shell production of the charged Higgs boson state, H^{pm }, arising from the two-Higgs-doublet mixing, and its semi-invisible decays via the mediator particle, a: H^{pm } rightarrow W^pm a (rightarrow chi chi ). Signal models with H^{pm } masses up to 1.5 TeV and a masses up to 350 GeV are excluded assuming a tan beta value of 1. For masses of a of 150 (250) GeV, tan beta values up to 2 are excluded for H^{pm } masses between 200 (400) GeV and 1.5 TeV. Signals with tan beta values between 20 and 30 are excluded for H^{pm } masses between 500 and 800 GeV.

Non-supersymmetric SO(10) models with Gauge and Yukawa coupling unification

We study a non-supersymmetric SO(10) Grand Unification Theory with a very high energy intermediate symmetry breaking scale in which not only gauge but also Yukawa coupling unification are enforced via suitable threshold corrections and matching conditions. For gauge unification, we focus on a few symmetry breaking patterns with the intermediate gauge groups text {SU}(4)_{textrm{C}} times text {SU}(2)_{textrm{L}} times text {SU}(2)_{textrm{R}} (Pati–Salam) and text {SU}(3)_{textrm{C}} times text {SU}(2)_{textrm{L}} times text {SU}(2)_{textrm{R}}times text {U}(1)_{{textrm{B}}-{textrm{L}}} (minimal left-right symmetry) assuming an additional global U(1) Peccei–Quinn symmetry, and having the Standard Model supplemented by a second Higgs doublet field at the electroweak scale. We derive the conditions as well as the approximate analytical solutions for the unification of the gauge coupling constants at the two-loop level and discuss the constraints from proton decay on the resulting high scale. Specializing to the case of the Pati–Salam intermediate breaking pattern, we then impose also the unification of the Yukawa couplings of third generation fermions at the high scale, again at the two-loop level. In the considered context, Yukawa unification implies a relation between the fermion couplings to the 10- and 126-dimensional scalar representations of the SO(10) group. We consider one such possible relation which is obtainable in an text {E}_6 model where the previous two scalar fields are part of a single multiplet. Taking into account some phenomenological features such as the absence of flavor changing neutral currents at tree-level, we derive constraints on the parameters of the low energy model, in particular on the ratio of the two Higgs doublets vacuum expectation values tan beta .

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.

Muon and electron (g-2) anomalies with non-holomorphic interactions in MSSM

The recent Fermilab muon g-2 result and the same for electron due to fine-structure constant measurement through {}^{133}textrm{Cs} matter-wave interferometry are probed in relation to MSSM with non-holomorphic (NH) trilinear soft SUSY breaking terms, referred to as NHSSM. Supersymmetric contributions to charged lepton (g-2)_l can be enhanced via the new trilinear terms involving a wrong Higgs coupling with left and right-handed scalars. Bino-slepton loop is used to enhance the SUSY contribution to g-2 where wino mass stays at 1.5 TeV and the left and right slepton mass parameters for the first two generations are considered to be the same. Unlike many MSSM-based analyses completed before, the model does not require a light electroweakino, or light sleptons, or unequal left and right slepton masses, or a very large higgsino mass parameter. In absence of popular UV complete models, we treat the NH terms at par with MSSM soft terms, in a model independent framework of Minimal Effective Supersymmetry. The first part of the analysis involves the study of (g-2)_mu constraint along with the limits from Higgs mass, B-physics, collider data, direct detection of dark matter (DM), while focusing on a higgsino DM which is underabundant in nature. We then impose the constraint from electron g-2 where a large Yukawa threshold correction (an outcome of NHSSM) and opposite signs of trilinear NH coefficients associated with mu and e fields are used to satisfy the dual limits of Delta {a_mu } and Delta {a_e} (where the latter comes with negative sign). Varying Yukawa threshold corrections further provide the necessary flavor-dependent enhancement of Delta {a_e}/m_e^2 compared to that of Delta {a_mu }/m_mu ^2. A larger Yukawa threshold correction through A^prime _e for y_e also takes away the direct proportionality of a_e with respect to tan beta . With a finite intercept, a_e becomes only an increasing function of tan beta . We identified the available parameter space in the two cases while also satisfying the ATLAS data from slepton pair production searches in the plane of slepton mass parameter and the mass of the lightest neutralino.

Two-loop improved predictions for mathbf {M_W} and mathbf {sin^2theta _{eff}} in Two-Higgs-Doublet models

We present the currently most precise predictions for the W-boson mass and the leptonic effective mixing angle in the aligned Two-Higgs-Doublet Model. The evaluation includes the full one-loop result, all known higher-order corrections of the Standard Model, and the non-standard two-loop contributions that increase with mass splittings between charged and neutral THDM Higgs bosons. They depend on tan beta and the soft Z_2-symmetry breaking parameter m_{12}^2 of the scalar potential, in addition to the non-standard boson masses. Whenever the one-loop corrections become large, the two-loop contributions yield substantial modifications of the predictions, which is of particular importance for the W mass where large mass shifts are required to reach the recently published final result of the CDF collaboration. Numerical results are shown for the dependence on the various non-standard parameters and in comparison with experimental data.

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.

Muon mathbf {g-2}, neutralino dark matter and stau NLSP

We explore the implications of resolving the muon g-2 anomaly in a SU(4)_c times SU(2)_L times SU(2)_R model, where the soft supersymmetry breaking scalar and gaugino masses break the left-right (LR) symmetry. A 2sigma resolution of the anomaly requires relatively light sleptons, chargino and LSP neutralino. The stau turns out to be the NLSP of mass m_{tilde{tau }}lesssim 400 GeV, and the sleptons from the first two families can be as heavy as about 800 GeV. The chargino is also required to be lighter than about 600 GeV to accommodate the muon g-2 solutions consistent with the dark matter relic density constraint. The dominant right-handed nature of the light slepton states suppress the sensitivity of possible signals which can be probed in Run3 experiments at the LHC. We also discuss the impact of accommodating the Higgs boson mass and the vacuum stability of the scalar potential for these solutions. Although a light stau can be compatible with the stability of the scalar potential, the Higgs boson mass constraint has a strong impact on the solutions with tan beta bounded from above, namely tan beta lesssim 20. The Higgsinos are heavier than about 4 TeV, and the LSP neutralino has the correct relic density if it is Bino-like. We identify stau–neutralino coannihilation as the dominant mechanism for realizing the desired dark matter relic density, with sneutrino–neutralino coannihiliation playing a minor role. These bino-like dark matter solutions can yield a spin-independent scattering cross-section on the order of 10^{-13}pb which hopefully, can be expected to be tested in the near future.

Zee model with quasidegenerate neutrino masses and where to find it

We present a Zee model with a family dependent Z_2 symmetry for radiative neutrino masses. Our motivation is to get a model that correctly describes neutrino oscillation phenomena, while at the same time offers definite predictions. The imposed Z_2 symmetry greatly reduces the number of free parameters in the model. These parameters are then determined from the neutrino data, from which one can study its outcomes. Our setup only admits quasidegenerate neutrino masses with the sum of neutrino masses between 100 and 130 meV, the effective Majorana mass between 20 and 40 meV, and the effective electron neutrino mass between 48 and 53 meV. The ratio of the vacuum expectation values of the Higgs doublets, tan beta , is found to be tan beta lesssim 0.5 and tan beta gtrsim 10. The former is ruled out by lepton flavor violation (LFV) processes, such as mu rightarrow egamma and mu rightarrow e conversion, which are determined up to two loops. For the latter, these LFV processes are within reach of the next generation of experiments. Moreover, for tan beta gtrsim 10, the couplings of heavy neutral scalars to dimuon are significant. If they are sufficiently light, i.e., lesssim 200 GeV, collider search for their decays into muon pair provides a stronger constraint on most parts of the model parameter space than the LFV ones.

Exploring the low tan beta region of two Higgs doublet models at the LHC

Current interpretations of the LHC results on two Higgs doublet models (2HDM) underestimate the sensitivity due to neglecting higher order effects. In this work, we revisit the impact of these effects using the current cross-section times branching ratio limits of the Arightarrow hZ, H rightarrow VV and Hrightarrow hh channels. With a degenerate heavy Higgs mass m_varPhi , we find that the LHC searches gain sensitivity to the small tan beta region after including loop corrections, even close to cos (beta -alpha )=0 which is not reachable at tree level for all types of 2HDM. For a benchmark point with m_varPhi =300 GeV, tan beta <1.8(1.2) can be probed for the Type-I(II) 2HDM model for cos (beta -alpha )=0. When the deviation from cos (beta -alpha )=0 is larger, the region for which current searches have exclusion potential becomes larger.

A minimal supersymmetric SU(5) missing-partner model

We explore a missing-partner model based on the minimal SU(5) gauge group with mathbf{75} , mathbf{50} and overline{mathbf{50 }} Higgs representations, assuming a super-GUT CMSSM scenario in which soft supersymmetry-breaking parameters are universal at some high scale M_{mathrm{in}} above the GUT scale M_{mathrm{GUT}}. We identify regions of parameter space that are consistent with the cosmological dark matter density, the measured Higgs mass and the experimental lower limit on tau (p rightarrow K^+ nu ). These constraints can be satisfied simultaneously along stop coannihilation strips in the super-GUT CMSSM with tan beta sim 3.5–5 where the input gaugino mass m_{1/2} sim 15–25 TeV, corresponding after strong renormalization by the large GUT Higgs representations between M_{mathrm{in}} and M_{mathrm{GUT}} to m_{mathrm{LSP}}, m_{{tilde{t}}_1} sim 2.5–5 TeV and m_{{tilde{g}}} sim 13–20 TeV, with the light-flavor squarks significantly heavier. We find that tau (p rightarrow K^+ nu ) lesssim 3 times 10^{34} years throughout the allowed range of parameter space, within the range of the next generation of searches with the JUNO, DUNE and Hyper-Kamiokande experiments.

Probing heavy charged Higgs bosons through bottom flavored hadrons in the H^+rightarrow bar{b}trightarrow B+X channel in 2HDM

Observing light or heavy charged Higgs bosons H^pm , lighter or heavier than the top quark, would be instant evidence of physics beyond the Standard Model. For this reason, in recent years searches for charged Higgs bosons have been in the center of attention of current colliders such as the CERN Large Hadron Collider (LHC). In spite of all efforts, no signal has been yet observed. Especially, the results of CMS and ATLAS experiments have excluded a large region in the MSSM m_{H^+}-tan beta parameter space for m_{H^+}=80{-}160 GeV corresponding to the entire range of tan beta up to 60. Therefore, it seems that one should concentrate on probing heavy charged Higgs bosons (m_{H^pm }>m_t) so in this context each new probing channel is welcomed. In this work, we intend to present our proposed channel to search for heavy charged Higgses through the study of scaled-energy distribution of bottom-flavored mesons (B) inclusively produced in charged Higgs decay, i.e., H^+rightarrow tbar{b}rightarrow B+X. Our study is carried out within the framework of the generic two Higgs doublet model (2HDM) using the massless scheme where the zero mass parton approximation is adopted for bottom quark.

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}.

Type-I thermal leptogenesis in Z_3-symmetric three Higgs doublet model

Our present work explores the possibility of neutrino mass generation through Type-I see-saw mechanism and provides an explanation of the baryon asymmetry of the Universe via thermal leptogenesis in the framework of a Z_3-symmetric three Higgs doublet model (3HDM) augmented with three right-handed neutrinos. Here the thermal leptogenesis is initiated by the out-of-equilibrium decay of the lightest heavy neutrino N_1. The constraints arising out of the scalar sector put strong bound on the model parameter tan beta , which in turn takes part in the computation of the lepton asymmetry epsilon . Lepton asymmetry being converted partially into the baryon asymmetry by electroweak sphelaron processes, will account for the required baryon asymmetry satisfying the current data. We therefore analyse the parameter space consistent with the constraints arising from neutrino oscillation, lepton asymmetry and baryon asymmetry together, last one turning out to be the most stringent one.

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.

A minimal SU(5) SuperGUT in pure gravity mediation

The lack of evidence for low-scale supersymmetry suggests that the scale of supersymmetry breaking may be higher than originally anticipated. However, there remain many motivations for supersymmetry including gauge coupling unification and a stable dark matter candidate. Models like pure gravity mediation (PGM) evade LHC searches while still providing a good dark matter candidate and gauge coupling unification. Here, we study the effects of PGM if the input boundary conditions for soft supersymmetry breaking masses are pushed beyond the unification scale and higher dimensional operators are included. The added running beyond the unification scale opens up the parameter space by relaxing the constraints on tan beta . If higher dimensional operators involving the SU(5) adjoint Higgs are included, the mass of the heavy gauge bosons of SU(5) can be suppressed leading to proton decay, prightarrow pi ^0 e^+, that is within reach of future experiments. Higher dimensional operators involving the supersymmetry breaking field can generate additional contributions to the A- and B-terms of order m_{3/2}. The threshold effects involving these A- and B-terms significantly impact the masses of the gauginos and can lead to a bino LSP. In some regions of parameter space the bino can be degenerate with the wino or gluino and give an acceptable dark matter relic density.

Search for neutral Higgs bosons within type-I 2HDM at future linear colliders

In this study, we investigate observability of the neutral scalar (H) and pseudoscalar (A) Higgs bosons in the framework of the type-I 2HDM at SM-like scenario at a linear collider operating at sqrt{s}= 500 and 1000 GeV. The signal process is e^- e^+ rightarrow A H rightarrow ZHHrightarrow jj b{bar{b}}b{bar{b}} where jj is a di-jet resulting from the Z boson decay and b{bar{b}} is a b-jet pair from scalar Higgs boson decay. Several benchmark scenarios with different mass hypotheses are studied. The assumed signal process is mainly motivated by the large decay rate of Arightarrow ZH (at high tan beta and enough Higgs boson mass splitting) and Hrightarrow b{bar{b}} in the type-I. After event generation the detector response is simulated based on the SiD detector at the ILC. The ISR and beamstrahlung effects are also included for each center of mass energy assuming unpolarized beams. The simulated events are analyzed to obtain candidate mass distributions of the Higgs bosons. Among standard model backgrounds, the top quark pair production process is the main background but is under control. Results indicate that, in all considered scenarios, both Higgs bosons H and A are observable with signals exceeding 5sigma with possibility of mass measurement. Final results are shown as 5sigma contours in (m_H,m_A) or (m_A,tan beta ) space.

MSSM Higgs benchmark scenarios for Run 2 and beyond: the low tan beta region

We propose two new benchmark scenarios for Higgs-boson searches in the Minimal Supersymmetric Standard Model (MSSM ). These scenarios are specifically designed for the low tan beta region. A light Higgs-boson mass prediction compatible with the observed value of 125,hbox {GeV} is ensured in almost the entire parameter space by employing a flexible supersymmetric (SUSY) mass scale, reaching values of up to 10^{16},hbox {GeV}. The MSSM Higgs-sector predictions are evaluated in an effective field theory (EFT ) framework that exhibits a Two-Higgs-Doublet-Model at the low scale. In the first scenario all SUSY particles are relatively heavy, whereas the second scenario features light neutralinos and charginos. Both scenarios are largely compatible with the most recent results from Run 2 of the LHC , and we highlight the main phenomenological features relevant for future LHC searches. In particular, we provide a detailed discussion of heavy Higgs-boson decays to neutralinos and charginos in the second scenario, and the arising collider signatures, in order to facilitate the design of dedicated LHC searches in the near future.