Search

We show that in a multi-Higgs model in which one Higgs fits the LHC 125 GeV state, one or more of the other Higgs bosons can mediate DM-nucleon interactions with maximal DM isospin violation being possible for appropriate Higgs-quark couplings, independent of the nature of DM. We then consider the explicit example of a Type II two-Higgs-doublet model, identifying the h or H as the 125 GeV state while the H or h, respectively, mediates DM-nucleon interactions. Finally, we show that if a stable scalar, S, is added then it can be a viable light DM candidate with correct relic density while obeying all direct and indirect detection limits., Two subsections are added to address the collider bounds from direct search for heavy Higgs bosons and from jet plus missing energy final states. The LUX (2013) bound considered in the previous version is replaced by the latest LUX (2016) bound and the SuperCDMS limit is taken into account. The conclusions remain unchanged. A very minor change made in the title and new references included

We present a 5D Z2-symmetric IR-UV-IR model with a warped KK-parity under which the bulk fields have towers of either even or odd KK-modes. We show that this Z2-symmetric geometry is equivalent to two times the UV-IR geometry (Randall-Sundrum model) provided each bulk field is subject to Neumann (or mixed) and Dirichlet boundary conditions at the UV-brane for even and odd fields, respectively. The 5D Standard Model (SM) bosonic sector is considered, such that in the 4D low-energy effective theory the Z2-even zero-modes correspond to the SM degrees of freedom, whereas the Z2-odd zero modes serve as a dark sector. In the zero-mode scalar sector, the even scalar mimics the SM Higgs boson, while the odd scalar (dark-Higgs) is stable and serves as a dark matter candidate. Implications for this dark matter are discussed; it is found that the dark-Higgs can provide only a small fraction of the observed dark matter abundance.

Given the disappearance of the 750 GeV di-photon LHC signal and the absence of signals at high mass in this and other channels, significant constraints on the mixed Higgs-radion of the five-dimensional Randall-Sundrum model arise. By combining all channels, these constraints place a significant radion-mass-dependent lower bound on the radion vacuum expectation value that is fairly independent of the amount of Higgs radion mixing., 23+1 pages, 11 figures and 1 table

We employ an $SU(2)$ bulk Higgs doublet as the stabilization field in Randall-Sundrum model with appropriate bulk and brane-localized potentials. The gauge hierarchy problem can be solved for an exponentially IR-localized Higgs background field with mild values of fundamental parameters of the 5D theory. We consider an IR-UV-IR background geometry with the 5D SM fields in the bulk such that all the fields have even and odd tower of KK-modes. The zero-mode 4D effective theory contains all the SM fields plus a stable scalar, which serves as a dark matter candidate., 8 pages, 4 figures. Talk given at the XXXIX International Conference of Theoretical Physics "Matter To The Deepest", Ustron, Poland. Based on arXiv:1504.03706

We explore the possibilities in two-Higgs-doublet models (2HDMs) of Type I and Type II for Higgs states with mass below about 60 GeV, i.e. less than half of the ~125 GeV mass of the observed SM-like Higgs boson. We identify the latter as either the lighter or the heavier CP-even state, h or H, and employ scans of the 2HDM parameter space taking into account all relevant theoretical and experimental constraints, including the most up-to-date Higgs signal strength measurements. We find that, in both Type I and Type II models, such light Higgs states are phenomenologically viable and can lead to interesting signatures. Part of the relevant parameter space may be testable with the existing 8 TeV LHC data, e.g. by looking for direct production of the light state via gg-fusion or bb-associated-production using its \tau^+ \tau^- and \mu^+ \mu^- decays at low invariant mass., Comment: 19 pages, 15 figures, references and a short comment added

I summarize the basic theory and selected phenomenology for the Higgs boson(s) of the standard model, the minimal supersymmetric model and some extensions thereof, including the next-to-minimal supersymmetric model.

We derive the effective potential for the Standard Model Higgs-boson sector interacting with Kaluza-Klein excitations of the graviton ($h_\mu^{\nu n}$) and the radion ($\phi$) and show that {\it only} the Standard Model vacuum solution of $\partial V(h)/\partial h =0$ (h is the Higgs field) is allowed. We then consider the consequences of the curvature-scalar mixing xi R \Hhat^\dagger \Hhat$ (where $\Hhat$ is a Higgs doublet field on the visible brane), which causes the physical mass eigenstates h and $\phi$ to be mixtures of the original Higgs and radion fields. First, we discuss the theoretical constraints on the allowed parameter space. Next, we give precise procedures for computing the h and $\phi$ couplings given the {\it physical} eigenstate masses, mh and $\mphi$, xi and the new physics scales of the model. We show that LEP/LEP2 data implies that not both the h and $\phi$ can be light. In the allowed region of parameter space, we examine numerically the couplings and branching ratios of the h and $\phi$ for several cases with $\mh=120\gev$ and $\mphi\leq 300\gev$. The resulting prospects for detection of the h and $\phi$ at the LHC, a future LC and a $\gam\gam$ collider are reviewed. For moderate $|\xi|$, both the anomalous $h\to gg$ coupling and (when $\mh>2\mphi$) the non-standard decay channel $h \to \phi\phi$ can substantially impact h discovery. Presence of the latter is a direct signature for non-zero xi. We find that $BR(h \to \phi\phi)$ as large as $30 \div 40 %$ is possible when $|\xi|$ is large. Conversely, if $\mphi>2\mh$ then $BR(\phi\to hh)$ is generally large. The feasibility of experimentally measuring the anomalous gg and $\gam\gam$ couplings of the h and $\phi$ is examined., Comment: 62 page, 30 figures. Because some figures had to be reduced in resolution, they will only accurately appear in magnified ghostview. For full abstract see paper

We summarize some of the unique physics capabilities of a e- e- collider and its companion facilities for e- γ and γγ collisions.

We extend the two-Higgs doublet models of Type I and Type II by adding a real gauge-singlet scalar S dark matter candidate (2HDMS models). We impose theoretical constraints deriving from perturbativity, stability, unitarity and correct electroweak symmetry breaking and require that the lightest CP-even Higgs, h, fit the LHC data for the $\sim 125.5$ GeV state at the $68\%$~C.L. after including existing constraints from LEP and B physics and LHC limits on the heavier Higgs bosons. We find that these models are easily consistent with the LUX and SuperCDMS limits on dark-matter-Nucleon scattering and the observed $\Omega h^2$ for S masses above about 55 GeV. At lower $m_S$, the situation is more delicate. For points with $m_S$ in the 6-25 GeV range corresponding to the CDMS~II and CRESST-II positive signal ranges, the dark-matter-Nucleon cross sections predicted by the Type I and Type II models more or less automatically fall within the $95\%-99\%$~C.L. signal region boundaries. Were it not for the LUX and SuperCDMS limits, which exclude all (almost all) such points in the case of Type I (Type II), this would be a success for the 2HDMS models. In fact, in the case of Type II there are a few points with 5.5 GeV $\leq m_S \leq$ 6.2 GeV that survive the LUX and SuperCDMS limits and fall within the CDMS~II 99\% C.L. signal region. Possibilities for dark matter to be isospin-violating in this 2HDMS context are also examined., Comment: 30 pages, 20 figures, 6 tables

We analyze the Two-Higgs-Doublet Models (2HDMs) of Type I and II for consistency with the latest measurements of the ~125.5 GeV Higgs-like signal at the LHC. To this end, we perform scans of the 2HDM parameter space taking into account all relevant pre-LHC constraints as well as the most recent limits coming from searches for heavy Higgs-like states at the LHC. The current status of the 2HDMs of Type I and II is discussed assuming that the observed 125.5 GeV state is one of the two CP-even Higgs bosons, either the lighter h or the heavier H. Implications for future experiments, including expectations regarding other lighter or heavier Higgs bosons are given. The possible importance of heavier Higgs bosons feeding the signals for the 125.5 GeV state is also evaluated., 52 pages, 32 figures, match to the published version

We consider the two-Higgs-doublet model as a framework in which to evaluate the viability of scenarios in which the sign of the coupling of the observed Higgs boson to down-type fermions (in particular, $b$-quark pairs) is opposite to that of the Standard Model (SM), while at the same time all other tree-level couplings are close to the SM values. We show that, whereas such a scenario is consistent with current LHC observations, both future running at the LHC and a future $e^+ e^-$ linear collider could determine the sign of the Higgs coupling to $b$-quark pairs. Discrimination is possible for two reasons. First, the interference between the $b$-quark and the $t$-quark loop contributions to the $ggh$ coupling changes sign. Second, the charged-Higgs loop contribution to the $\gamma \gamma h$ coupling is large and fairly constant up to the largest charged-Higgs mass allowed by tree-level unitarity bounds when the $b$-quark Yukawa coupling has the opposite sign from that of the SM (the change in sign of the interference terms between the $b$-quark loop and the $W$ and $t$ loops having negligible impact)., Comment: 28 pages, 21 figures

We study the use of polarization asymmetries at a muon collider to determine the CP-even and CP-odd couplings of a Higgs boson to $\mu^+mu^-$. We determine achievable accuracy as a function of beam polarization and luminosity. The appropriate techniques for dealing with the polarization precession are outlined. Strategies especially appropriate for a two-Higgs-doublet model (including the MSSM) are given. Our general conclusion is that polarization will be very useful, especially if the proton source is such that full luminosity in the storage ring can be retained even after imposing cuts on the originally accepted muons necessary for $P\gsim 0.4$ for each beam., Comment: 33 pages, 10 figures, equations.sty

Already in the simplest two-Higgs-doublet model with CP violation in the Higgs sector, the $3\times3$ mixing matrix for the neutral Higgs bosons can substantially modify their couplings, thereby endangering the ``classical'' Higgs search strategies. However, there are sum rules relating Yukawa and Higgs-Z couplings which ensure that the ZZ, $b\anti b$ and $t\anti t$ couplings of a given neutral 2HDM Higgs boson cannot all be simultaneously suppressed. This result implies that any single Higgs boson will be detectable at an e^+e^- collider if the Z+Higgs, $b\anti b+$Higgs {\it and} $t\anti t+$Higgs production channels are all kinematically accessible {\it and} if the integrated luminosity is sufficient. We explore, as a function of Higgs mass, the luminosity required to guarantee Higgs boson detection, and find that for moderate $\tan\beta$ values the needed luminosity is unlikely to be available for all possible mixing scenarios. The additional difficulties for the case when the two-doublet Higgs sector is extended by adding one more singlet are summarized. Implications of the sum rules for Higgs discovery at the Tevatron and LHC are briefly discussed., Comment: 16 pages, 4 postscript figures, references added in replacement

Assuming perturbativity up to a high energy scale $\ensuremath{\sim}{10}^{16}\mathrm{GeV}$, we demonstrate that a future ${e}^{+}{e}^{\ensuremath{-}}$ linear collider operating at $\sqrt{s}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}500\mathrm{GeV}$ with $\ensuremath{\int}L\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}500{\mathrm{fb}}^{\ensuremath{-}1}$ per year (such as the recently proposed TESLA facility) will detect a Higgs boson signal regardless of the complexity of the Higgs sector and of how the Higgs bosons decay.

We demonstrate that the relative size of the CP-even and CP-odd couplings of a Higgs boson to $t\anti t$ can be determined at the LHC at a level that is very useful in discriminating between models, provided that a Higgs signal can be observed at a reasonable $S/\sqrt B$ level in the $t\anti t\h$ (with $\h\to\gamma\gamma$ or $b\anti b)$ channels. In particular, the CP-even nature of a SM-like Higgs boson's coupling to $t\anti t$ can be confirmed with very substantial statistical significance using the $t\anti t \h$ ($\h\to \gamma\gamma$) production/decay mode. The key to achieving good discrimination between models is to make full use of the difference in the final state distributions for different ratios of the CP-even to CP-odd couplings. For our analysis, we employ the very convenient and simple optimal analysis procedures derived previously., Comment: 12 pages

We demonstrate that supersymmetric decays, as typified by the predictions of several grand unified theory (GUT)-scale boundary condition choices, do not prevent detection of Z{sup {star}}{r_arrow}H{sup 0}A{sup 0},H{sup +}H{sup {minus}}, at a 1{minus}4TeV e{sup +}e{sup {minus}} or {mu}{sup +}{mu}{sup {minus}} collider operating at anticipated luminosity. For much of the parameter space the relative branching ratios for various supersymmetric (SUSY) and non-SUSY decays can be measured with sufficient accuracy that different GUT-scale boundary condition choices can be distinguished from one another at a very high confidence level. {copyright} {ital 1997} {ital The American Physical Society}

We analyze the extent to which the LHC and Tevatron results as of the end of 2012 constrain invisible (or undetected) decays of the Higgs boson-like state at ~ 125 GeV. To this end we perform global fits for several cases: 1) a Higgs boson with Standard Model (SM) couplings but additional invisible decay modes; 2) SM couplings to fermions and vector bosons, but allowing for additional new particles modifying the effective Higgs couplings to gluons and photons; 3) no new particles in the loops but tree-level Higgs couplings to the up-quarks, down-quarks and vector bosons, relative to the SM, treated as free parameters. We find that in the three cases invisible decay rates of 23%, 61%, 88%, respectively, are consistent with current data at 95% confidence level (CL). Limiting the coupling to vector bosons, CV, to CV < 1 in case 3) reduces the allowed invisible branching ratio to 56% at 95% CL. Requiring in addition that the Higgs couplings to quarks have the same sign as in the SM, an invisible rate of up to 36% is allowed at 95% CL. We also discuss direct probes of invisible Higgs decays, as well as the interplay with dark matter searches., 14 pages, 8 figures; v2: extended discussion on ZH associated production, references added, minor corrections; v4: matches final version published in Phys. Lett. B

Performing a fit to all publicly available data, we analyze the extent to which the latest results from the LHC and Tevatron constrain the couplings of the Higgs boson-like state at ~ 125 GeV. To this end we assume that only Standard Model (SM) particles appear in the Higgs decays, but tree-level Higgs couplings to the up-quarks, down-quarks and vector bosons, relative to the SM are free parameters. We also assume that the leptonic couplings relative to the SM are the same as for the down-quark, and a custodial symmetry for the V=W,Z couplings. In the simplest approach, the effective Higgs couplings to gluons and photons are computed in terms of the previous parameters. This approach is also applied to Two-Higgs-Doublet Models of Type I and Type II. However, we also explore the possibility that the net Higgs to gluon-gluon and gamma-gamma couplings have extra loop contributions coming from Beyond-the-Standard Model physics. We find that the SM p-value ~ 0.5 is more than 2 sigma away from fits in which: a) there is some non-SM contribution to the gamma-gamma coupling of the Higgs; or b) the sign of the top quark coupling to the Higgs is opposite that of the W coupling. In both these cases p-values ~ 0.9 can be achieved. Since option b) is difficult to realize in realistic models, it would seem that new physics contributions to the effective couplings of the Higgs are preferred., 25 pages, 11 figures; v2: minor corrections, references added; v3: acknowledgement added

The optimal procedure for extracting the coefficients of different components of a cross section which takes the form of unknown coefficients times functions of known kinematical form is developed. When applied to e + e → tt+Higgs production at √ s = 1TeV and integrated luminosity of 200 fb 1 , we find that the tt →Higgs CP-even and CP-odd couplings and, to a lesser extent, the ZZ →Higgs (CP-even) coupling can be extracted with reasonable errors, assuming the Higgs sector parameter choices yield a significant production rate. Indeed, the composition of a mixed-CP Higgs eigenstate can be determined with sufficient accuracy that a SM-like CPeven Higgs boson can be distinguished from a purely CP-odd Higgs boson at a high level of statistical significance, and vice versa.

We develop diagnostic tools that would provide incontrovertible evidence for the presence of more than one Higgs boson near 125 GeV in the LHC data., Comment: 4 pages, 2 figures

We explore the parameter choices in the five-dimensional Randall-Sundrum model with the inclusion of Higgs-radion mixing that can describe current LHC hints for one or more Higgs boson signals., Comment: 14 pages, 8 figures. Revised version includes additional discussion of possible influence of 5D Yukawa couplings and higher KK states on $gg$ and $\gamma\gamma$ couplings of the unmixed Higgs boson

We examine GUT-scale NMSSM scenarios in which {\it both} $h_1$ and $h_2$ lie in the 123 -- 128 GeV mass range. Very substantially enhanced $\gamma\gamma$ and other rates are possible. Broadened mass peaks are natural., Comment: 8 pages, 8 figures

We examine the level of enhancement that can be achieved in the ZZ and \gamma\gamma channels for a two-Higgs-doublet model Higgs boson (either the light h or the heavy H) with mass near 125 GeV after imposing all constraints from LEP data, B physics, precision electroweak data, vacuum stability, unitarity and perturbativity. The latter constraints restrict substantially the possibilities for enhancing the gg -> h -> \gamma\gamma or gg -> H -> \gamma\gamma signal relative to that for the SM Higgs, hSM. Further, we find that a significant enhancement of the gg -> h -> \gamma\gamma or gg -> H -> \gamma\gamma signal in Type II models is possible only if the gg -> h -> ZZ or gg -> H -> ZZ mode is even more enhanced, a situation disfavored by current data. In contrast, in the Type I model one can achieve enhanced rates in the \gamma\gamma final state for the h while having the ZZ mode at or below the SM rate - the largest [gg -> h -> \gamma\gamma]/[gg -> hSM -> \gamma\gamma] ratio found is of order ~1.3 when the two Higgs doublet vacuum expectation ratio is tan\beta = 4 or 20 and the charged Higgs boson has its minimal LEP-allowed value of m_{H^\pm} = 90 GeV., Comment: 15 pages, 9 figures

We present a set of recommendations for the presentation of LHC results on searches for new physics, which are aimed at providing a more efficient flow of scientific information between the experimental collaborations and the rest of the high energy physics community, and at facilitating the interpretation of the results in a wide class of models. Implementing these recommendations would aid the full exploitation of the physics potential of the LHC., Comment: 17 pages, no figures; v2: author added

We consider the production of the Higgs boson(s) of both the standard model and the minimal supersymmetric model via the collision of two polarized backscattered laser photons at an [ital e][sup +][ital e[minus]] linear collider. The anticipated photon-photon luminosity should be sufficient to allow detection of any one of these Higgs bosons over a significant range of Higgs boson masses. In particular, the Higgs boson mass reach in the [gamma][gamma] collider mode may be somewhat larger than that of the corresponding [ital e][sup +][ital e[minus]] linear collider. Moreover, [gamma][gamma][r arrow][ital H] will provide a measure of the [gamma][gamma][ital H] coupling which arises at one loop, and therefore is potentially sensitive to all charged particles which gain mass through the Higgs mechanism.

For some choices of soft SUSY-breaking parameters, the LSP is a stable neutralino [Formula: see text], the NLSP is a chargino [Formula: see text] almost degenerate in mass with the LSP [Formula: see text], and all other sparticles are relatively heavy. We discuss the potential of hadron colliders, particularly the LHC, for studying such models.

We outline the motivations for having a light Higgs boson with fairly SM-like couplings to WW, ZZ but with unusual decays that elude LEP limits and that will also make its detection at the LHC quite challenging. The Next-to-Minimal Supersymmetric Model provides a very appealing model of this type.

We classify the variety of low-energy supersymmetric signatures that can be probed at future colliders. We focus on phenomena associated with the minimal supersymmetric extension of the Standard Model. The structure of the supersymmetry-breaking introduces additional model assumptions. The approaches considered here are supergravity-mediated and gauge-mediated supersymmetry-breaking. Alternative phenomenologies arising in non-minimal and/or R-parity-violating approaches are also briefly examined.

The {ital CP}-odd Higgs boson {ital A}{sup 0} of a nonminimal Higgs model possesses no tree-level couplings to vector-boson pairs. As a result, many of the techniques employed to search for the standard model Higgs boson at the Superconducting Super Collider (SSC) and CERN Large Hadron Collider (LHC) are not likely to be useful in searches for the {ital A}{sup 0}. This paper focuses on the phenomenology of {ital A}{sup 0} production and decay in the minimal supersymmetric model. We evaluate a comprehensive set of branching ratios for {ital A}{sup 0} (which includes all two-body tree-level and one-loop decays into nonsupersymmetric final states), including the effects of leading-log radiative corrections. The one-loop decay {ital A}{sup 0}{r arrow}{ital ZZ} leads to the gold-plated'' signature {ital ZZ}{r arrow}{ital l}{sup +}{ital l{minus}}{ital l+}{ital l{minus}} and provides an observable signature for {ital A}{sup 0} production at the SSC and LHC only over a very narrow region of parameter space. More promising signatures for the {ital A}{sup 0} are also discussed.

We define a particularly useful asymmetry in t→W+b decays, which is sensitive to non-standard sources of CP violation. Prospects for observation of the predicted asymmetry at a hadron collider are estimated. As an illustration, the asymmetry arising from loop diagrams involving the neutral Higgs bosons of a two-doublet Higgs model with CP-violating neutral sector is computed.

The next-to-minimal supersymmetric model with a light doubletlike CP-odd Higgs boson and small tan{beta} can satisfy all experimental limits on Higgs bosons even with light superpartners. In these scenarios, the two lightest CP-even Higgs bosons, h{sub 1} and h{sub 2}, and the charged Higgs boson, h{sup +}, can all be light enough to be produced at CERN LEP and yet have decays that have not been looked for or are poorly constrained by existing collider experiments. The channel h{sub 1}{yields}a{sub 1}a{sub 1} with a{sub 1}{yields}{tau}{sup +}{tau}{sup -} or 2j is still awaiting LEP constraints for m{sub h{sub 1}}>86 or 82 GeV, respectively. LEP data may also contain e{sup +}e{sup -}{yields}h{sub 2}a{sub 1} events where h{sub 2}{yields}Za{sub 1} is the dominant decay, a channel that was never examined. Decays of the charged Higgs bosons are often dominated by H{sup {+-}}{yields}W{sup {+-}}{sup (}*{sup )}a{sub 1} with a{sub 1}{yields}gg, cc, and {tau}{sup +}{tau}{sup -}. This is a channel that has so far been ignored in the search for t{yields}h{sup +}b decays at the Tevatron. A specialized analysis might reveal a signal. The light a{sub 1} might be within the reach of B factories via {upsilon}{yields}{gamma}a{sub 1} decays. We study typical mass ranges and more » branching ratios of Higgs bosons in this scenario and compare these scenarios where the a{sub 1} has a large doublet component to the more general scenarios with arbitrary singlet component for the a{sub 1}. « less

We show that the existing CDF $L=630 pb^{-1}$ Tevatron data on $pp\to ��^+��^- + X$ places substantial limits on a light CP-odd Higgs boson $a$ with $m_a2m_��$ for which $BR(a\to ��^+��^-)$ is relatively small. Extrapolation of this existing CDF analysis to $L=10 fb^{-1}$ suggests that Tevatron limits on the $a b\anti b$ coupling strength in the region $m_a>8\gev$ could be comparable to or better than limits from Upsilon decays in the $m_a, 25 pages, 12 figures, updated LHC estimates and table based on ATLAS-related input now included (v4 and v5). In addition, comments regarding final ALEPH limits in the Z+4\tau channel are included in v5.

We compute the magnitude of flavor changing neutral current (FCNC) decays of the t quark and of the Z boson expected in a two-Higgs doublet model. The charged Higgs boson couplings are constrained to be consistent with errors with KLKS mixing, B0d− B 0 d mixing, and the observed ratio of b→u/b→c decays. We find that large corrections to the predictions of the standard model are possible, but that even the maximum possible levels for FCNC decays are so small as to make their detection very difficult.

We amalgamate the many experimental limits on the $ab\anti b$ coupling of a light CP-odd Higgs boson, $a$, including model-dependence coming from the ratio of the $at\anti t$ to the $a b\anti b$ coupling. We then employ these limits to analyze the extent to which a light $a$ can make a significant contribution to the discrepancy, $\Delta a_\mu$, between the experimentally observed $a_\mu$ and that predicted by the standard model. In a "model-independent" framework and in the context of a general two-Higgs-doublet model this is a significant possibility. In contrast, the minimal supersymmetric model is too strongly constrained (after combining experimental and theoretical input) to allow a CP-odd-$a$ explanation of $\Delta a_\mu$. The next-to-minimal supersymmetric model allows more freedom and the light $a$ of the model could explain the full $\Delta a_\mu$ if $9.2\gev, Comment: 12 pages, 6 figures, revised and expanded

Old and new ideas regarding Higgs physics are reviewed. We first summarize the quadratic divergence / hierarchy problem which strongly suggests that the SM Higgs sector will be supplemented by new physics at high scales. We next consider means for delaying the hierarchy problem of the SM Higgs sector to unexpectedly high scales. We then outline the properties of the most ideal Higgs boson. The main advantages of a supersymmetric solution to the high scale problems are summarized and the reasons for preferring the next-to-minimal supersymmetric model over the minimal supersymmetric model in order to achieve an ideal Higgs are emphasized. This leads us to the strongly motivated scenario in which there is a Higgs $h$ with SM-like $WW,ZZ$ couplings and $\mh\sim 100\gev$ that decays via $h\to aa$ with $m_a2m_\tau$ is preferred, implying $a\to \tau^+ \tau^-$. The means for detecting an $h\to aa\to 4\tau$ signal are then discussed. Some final cautionary and concluding remarks are given., Comment: 15 pages, 9 figures

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., 53 pages, review intended for Annual Reviews of Nuclear Science. Final corrections and references now included

I specify the characteristics of a Higgs boson that would be “ideal” in the light of current data and theoretical attractiveness. I then review why it is that the Higgs bosons of the Standard Model and the Minimal Supersymmetric Model cannot be ideal whereas the lightest Higgs boson of the Next to Minimal Supersymmetric Model can be ideal. Experimental consequences for Higgs and supersymmetry discovery are then reviewed. I then examine the alternatives to the NMSSM in which the MSSM is extended via an extra U(1) symmetry.

We consider constraints imposed on the top quark and on the charged Higgs boson of a two-doublet model by experimental results for K 0 − K 0 mixing, B d − B d mixing and the ratio of b → u to b → c decays.