arXiv subjects

Howard Baer

Publications and source records attributed to Howard Baer.

At least 37 records · Page 2Linked to original sources

arXiv2024

Weak scale supersymmetry emergent from the string landscape

Superstring flux compactifications can stabilize all moduli while leading to an enormous number of vacua solutions, each leading to different $4-d$ laws of physics. While the string landscape provides at present the only plausible explanation for the size of the cosmological constant, it may also predict the form of weak scale supersymmetry which is expected to emerge. Rather general arguments suggest a power-law draw to large soft terms, but these are subject to an anthropic selection of not-too-large a value for the weak scale. The combined selection allows one to compute relative probabilities for the emergence of supersymmetric models from the landscape. Models with weak scale naturalness appear most likely to emerge since they have the largest parameter space on the landscape. For finetuned models such as high scale SUSY or split SUSY, the required weak scale finetuning shrinks their parameter space to tiny volumes, making them much less likely to appear compared to natural models. Probability distributions for sparticle and Higgs masses from natural models show a preference for Higgs mass $m_h\sim 125$ GeV with sparticles typically beyond present LHC limits, in accord with data. From these considerations, we briefly describe how natural SUSY is expected to be revealed at future LHC upgrades. This article is a contribution to the Special Edition of the journal {\it Entropy} honoring Paul Frampton on his 80th birthday.

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arXiv2024

Supersymmetry with scalar sequestering

Supersymmetric models with a strongly interacting superconformal hidden sector (HS) may drive soft SUSY breaking scalar masses, bilinear soft term Bμand Higgs combinations m_{H_{u,d}}^2+μ^2 to small values at some intermediate scale, leading to unique sparticle mass spectra along with possibly diminished finetuning in spite of a large superpotential $μ$ parameter. We set up a computer code to calculate such spectra, which are then susceptible to a variety of constraints: 1. possible charge-or-color breaking (CCB) minima in the scalar potential, 2. unbounded from below (UFB) scalar potential, 3. improper electroweak symmetry breaking, 4. a charged or sneutrino lightest SUSY particle (LSP), 5. generating m_h~ 125 GeV, 6. consistency with LHC sparticle mass limits, and 7. naturalness. We find this bevy of constraints leaves little or no viable parameter space for the case where hidden sector dynamics dominates MSSM running, even for the case of non-universal gaugino masses. For the case with moderate HS running with comparable MSSM running, and with universal gaugino masses, then the finetuning is ameliorated, but nonetheless remains high. Viable spectra with moderate HS running and with low finetuning and large mu can be found for non-universal gaugino masses.

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arXiv2024

Winos from natural SUSY at the high luminosity LHC

In natural supersymmetric models defined by no worse than a part in thirty electroweak fine-tuning, winos and binos are generically expected to be much heavier than higgsinos. Moreover, the splitting between the higgsinos is expected to be small, so that the visible decay products of the heavier higgsinos are soft, rendering the higgsinos quasi-invisible at the LHC. Within the natural SUSY framwork, heavy electroweak gauginos decay to W, Z or h bosons plus higgsinos in the ratio ~2:1:1, respectively. This is in sharp contrast to models with a bino-like lightest superpartner and very heavy higgsinos, where the charged (neutral) wino essentially always decays to a W (h) boson and an invisible bino. Wino pair production at the LHC, in natural SUSY, thus leads to VV, Vh and hh+MET final states (V=W, Z) where, for TeV scale winos, the vector bosons and h daughters are considerably boosted. We identify eight different channels arising from the leptonic and hadronic decays of the vector bosons and the decay h-> b\bar{b}, each of which offers an avenue for wino discovery at the high luminosity LHC (HL-LHC). By combining the signal in all eight channels we find, assuming \sqrt{s}=14 TeV and an integrated luminosity of 3000 fb^{-1}, that the discovery reach for winos extends to m(wino)~1.1~TeV, while the 95% CL exclusion range extends to a wino mass of almost 1.4~TeV. We also identify ``higgsino specific channels'' which could serve to provide 3σevidence that winos lighter than 1.2~TeV decay to light higgsinos rather than to a bino-like LSP, should a wino signal appear at the HL-LHC.

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arXiv2023

Natural anomaly-mediation from the landscape with implications for LHC SUSY searches

Supersymmetric models with the anomaly-mediated SUSY breaking (AMSB) arose in two different settings: 1. extra-dimensional models where SUSY breaking occurred in a sequestered sector and 2. 4-d models with dynamical SUSY breaking in a hidden sector where scalars gain masses of order the gravitino mass m_{3/2} but with gauginos and trilinear soft terms of the AMSB form. Both have run into serious conflicts with 1. LHC sparticle and Higgs mass constraints, 2. constraints from wino-like WIMP dark matter searches and 3. bounds from naturalness. These conflicts may be avoided by introducing minor changes to the underlying phenomenological models consisting of non-universal bulk scalar Higgs masses and A-terms, providing a setting for {\it natural anomaly-mediation} (nAMSB). In nAMSB, the wino is still expected to be the lightest of the gauginos, but the higgsinos are expected to be the lightest electroweakinos (EWinos) in accord with naturalness. We examine what sort of spectra are expected to emerge when nAMSB arises from a string landscape setting. We explore the LHC phenomenology of nAMSB models via higgsino pair production and wino pair production. We characterize the dominant LHC signatures arising from the remaining patch of parameter space which should be fully testable at high-luminosity LHC via EWino pair production searches.

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arXiv2023

Top squarks from the landscape at high luminosity LHC

Supersymmetric models with low electroweak finetuning are expected to be more prevalent on the string landscape than finetuned models. We assume a fertile patch of landscape vacua containing the minimal supersymmetric standard model (MSSM) as low energy/weak scale effective field theory (LE-EFT). Then, a statistical pull by the landscape to large soft terms is balanced by the requirement of a derived value of the weak scale which is not too far from its measured value in our universe. Such models are characterized by light higgsinos in the few hundred GeV range whilst top squarks are in the 1-2.5 TeV range with large trilinear soft terms which helps to push m_h~ 125 GeV. Other sparticles are generally beyond current LHC reach and the BR(b -> sγ) branching fraction is nearly equal to its SM value. The light top-squarks decay comparably via \tst_1 -> b\tchi_1^+ and \tst_1 -> t\tchi_{1,2}^0 yielding mixed final states of b\bar{b}+MET, t\bar{b}/\ \bar{t}b + MET and t\bar{t}+ MET. We evaluate prospects for top squark discovery at high-luminosity (HL) LHC for the well-motivated case of natural SUSY from the landscape. We find for HL-LHC a 5σreach out to m_{\tst_1}~ 1.7 TeV and a 95\% CL exclusion reach to m_{\tst_1} ~ 2 TeV. These reaches cover {\it most} (but not all) of the allowed stringy natural parameter space!

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arXiv2023

Prospects for charged Higgs bosons in natural SUSY models at the high-luminosity LHC

We continue our examination of prospects for discovery of heavy Higgs bosons of natural SUSY (natSUSY) models at the high luminosity LHC (HL-LHC), this time focussing on charged Higgs bosons. In natSUSY, higgsinos are expected at the few hundred GeV scale whilst electroweak gauginos inhabit the TeV scale and the heavy Higgs bosons, H, A and H^\pm could range up tens of TeV without jeopardizing naturalness. For TeV-scale heavy SUSY Higgs bosons H, A and H^\pm, as currently required by LHC searches, SUSY decays into gaugino plus higgsino can dominate H^\pm decays provided these decays are kinematically accessible. The visible decay products of higgsinos are soft making them largely invisible, whilst the gauginos decay to W, Z or h plus missing transverse energy (MET). Charged Higgs bosons are dominantly produced at LHC14 via the parton subprocess, gb-> H^\pm t. In this paper, we examine the viability of observing signtures from H^\pm -> τν, H^\pm -> tb and H^\pm -> W, Z, h + MET events produced in association with a top quark at the HL-LHC over large Standard Model (SM) backgrounds from (mainly) t\bar{t}, t\bar{t}V and t\bar{t}h production (where V=W, Z). We find that the greatest reach is found via the SM H^\pm(-> τν) +t channel with a subdominant contribution from the H^\pm(-> tb) +t channel. Unlike for neutral Higgs searches, the SUSY decay modes appear to be unimportant for H^\pm searches at the HL-LHC. We delineate regions of the m_A vs. \tanβplane, mostly around m_A \sim 1-2 TeV, where signals from charged Higgs bosons would serve to confirm signals of a heavy, neutral Higgs boson at the 5σlevel or, alternatively, to exclude heavy Higgs bosons at the 95% confidence level at the high luminosity LHC.

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arXiv2023

On practical naturalness and its implications for weak scale supersymmetry

We revisit the various measures of naturalness for models of weak scale supersymmetry including 1. electroweak (EW) naturalness, 2. naturalness via sensitivity to high scale parameters (EENZ/BG), 3. sensitivity of Higgs soft term due to high scale (HS) radiative corrections and 4. stringy naturalness (SN) from the landscape. The EW measure is most conservative and seems unavoidable; it is also model independent in that its value is fixed only by the weak scale spectra which ensues, no matter which model is used to generate it. The EENZ/BG measure is ambiguous depending on which ``parameters of ignorance'' one includes in the low energy effective field theory (LE-EFT). For models with calculable soft breaking terms, then the EENZ/BG measure reduces to the tree-level EW measure. The HS measure began life as a figurative expression and probably shouldn't be taken more seriously than that. SN is closely related to EW naturalness via the atomic principle, although it is also sensitive to the distribution of soft terms on the landscape. If the landscape favors large soft terms, as in a power law distribution, then it favors m(h) ~ 125 GeV along with sparticles beyond present LHC reach. In this context, SN appears as a probability measure where more natural models are expected to be more prevalent on the landscape than finetuned models. We evaluate by how much the different measures vary against one another with an eye to determining by how much they may overestimate finetuning; we find overestimates can range up to a factor of over 1000. In contrast to much of the literature, we expect the string landscape to favor EW natural SUSY models over finetuned models so that the landscape is not an alternative to naturalness.

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arXiv2023

Dark matter and dark radiation from the early universe with a modulus coupled to the PQMSSM

The supersymmetrized DFSZ axion model is especially compelling in that it contains 1. the SUSY solution to the gauge hierarchy problem, 2. the Peccei-Quinn (PQ) solution to the strong CP problem and 3. the Kim-Nilles solution to the SUSY mu problem. In a string setting, where a discrete R-symmetry ({\bf Z}_{24}^R for example) may emerge from the compactification process, a high-quality accidental axion (accion) can emerge from the accidental, approximate remnant global U(1)_{PQ} symmetry where the decay constant f_a is linked to the SUSY breaking scale, and is within the cosmological sweet zone. In this setup, one also expects the presence of stringy remnant moduli fields ϕ_i. Here, we consider the situation of a single light modulus ϕcoupled to the PQMSSM in the early universe, with mixed axion plus higgsino-like WIMP dark matter. We evaluate dark matter and dark radiation production via nine coupled Boltzmann equations and assess the severity of the cosmological moduli problem (CMP) along with dark matter and dark radiation production rates. We find that typically the light modulus mass should be m_ϕ>~ 10^4 TeV to avoid the moduli-induced dark matter overproduction problem. If one is able to (anthropically) tune the modulus field amplitude, we find a value of ϕ_0 <~ 10^{-7}m_P would be required to solve the overall CMP.

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arXiv2023

The International Linear Collider: Report to Snowmass 2021

The International Linear Collider (ILC) is on the table now as a new global energy-frontier accelerator laboratory taking data in the 2030s. The ILC addresses key questions for our current understanding of particle physics. It is based on a proven accelerator technology. Its experiments will challenge the Standard Model of particle physics and will provide a new window to look beyond it. This document brings the story of the ILC up to date, emphasizing its strong physics motivation, its readiness for construction, and the opportunity it presents to the US and the global particle physics community.

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arXiv2022

Detecting heavy neutral SUSY Higgs bosons decaying to sparticles at the high-luminosity LHC

In supersymmetry (SUSY) models with low electroweak naturalness (natSUSY), which have been suggested to be the most likely version of SUSY to emerge from the string landscape, higgsinos are expected at the few hundred GeV scale whilst electroweak gauginos inhabit the TeV scale. For TeV-scale heavy neutral SUSY Higgs bosons H and A, as currently required by LHC searches, then the dominant decay modes of H, A are into gaugino plus higgsino provided these decays are kinematically open. The light higgsinos decay to soft particles so are largely invisible whilst the gauginos decay to W, Z or h plus missing transverse energy (MET). Thus, we examine the viability of H,A-> W+MET, Z+MET and h+MET signatures at the high luminosity LHC (HL-LHC) in light of large Standard Model (SM) backgrounds from (mainly) t\bar{t}, VV and Vh production (where V=W, Z). We also examine whether these signal channels can be enhanced over backgrounds by requiring the presence of an additional soft lepton from the decays of the light higgsinos. We find significant regions in the vicinity of m_A~ 1-2 TeV of the m_A vs. \tanβplane which can be probed at the high luminosity LHC using these dominant signatures by HL-LHC at 5σand at the 95% confidence level (CL).

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arXiv2022

Report of the Topical Group on Physics Beyond the Standard Model at Energy Frontier for Snowmass 2021

This is the Snowmass2021 Energy Frontier (EF) Beyond the Standard Model (BSM) report. It combines the EF topical group reports of EF08 (Model-specific explorations), EF09 (More general explorations), and EF10 (Dark Matter at Colliders). The report includes a general introduction to BSM motivations and the comparative prospects for proposed future experiments for a broad range of potential BSM models and signatures, including compositeness, SUSY, leptoquarks, more general new bosons and fermions, long-lived particles, dark matter, charged-lepton flavor violation, and anomaly detection.

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arXiv2022

TF08 Snowmass Report: BSM Model Building

We summarize the state of Beyond the Standard Model (BSM) model building in particle physics for Snowmass 2021, focusing mainly on several whitepaper contributions to BSM model building (TF08) and closely related areas.

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arXiv2022

Fine-tuned vs. natural supersymmetry: what does the string landscape predict?

A vast array of (metastable) vacuum solutions arise from string compactifications, each leading to different 4-d laws of physics. The space of these solutions, known as the string landscape, allows for an environmental solution to the cosmological constant problem. We examine the possibility of an environmental solution to the gauge hierarchy problem. We argue that the landscape favors softly broken supersymmetric models over particle physics models containing quadratic divergences, such as the Standard Model. We present a scheme for computing relative probabilities for supersymmetric models to emerge from the landscape. The probabilities are related to the likelihood that the derived value of the weak scale lies within the Agrawal et al. (ABDS) allowed window of values leading to atoms as we know them. This then favors natural SUSY models over unnatural (SUSY and other) models via a computable probability measure.

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arXiv2022

Prospects for heavy neutral SUSY Higgs scalars in the hMSSM and natural SUSY at LHC upgrades

We examine production and decay of heavy neutral SUSY Higgs bosons pp-> H,\ A -> τ\barτ within the hMSSM and compare against a perhaps more plausible natural supersymmetry scenario dubbed m_h^{125}({\rm nat}) which allows for a natural explanation for m_{weak}\simeq m_{W,Z,h}\sim 100 GeV while maintaining m_h\simeq 125 GeV. We evaluate signal against various Standard Model backgrounds from γ,Z ->τ\barτ, t\bar{t} and vector boson pair production VV. We combine the transverse mass method for back-to-back (BtB) taus along with the ditau mass peak m_{ττ} method for acollinear taus as our signal channels. This technique ultimately gives a boost to the signal significance over the standard technique of using just the BtB signal channel. We evaluate both the 95% CL exclusion and 5σdiscovery reach in the m_A vs. \tanβplane for present LHC with 139 fb^{-1}, Run 3 with 300 fb^{-1} and high luminosity LHC (HL-LHC) with 3000 fb^{-1} of integrated luminosity. For \tanβ=10, the exclusion limits range up to m_A\sim 1, 1.1 and 1.4 TeV, respectively. These may be compared to the range of m_A values gleaned from a statistical analysis of the string landscape wherein m_A can range up to ~8 TeV.

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arXiv2022

Radiative natural supersymmetry emergent from the string landscape

In string theory with flux compactifications, anthropic selection for structure formation from a discretuum of vacuum energy values provides at present our only understanding of the tiny yet positive value of the cosmological constant. We apply similar reasoning to a toy model of the multiverse restricted to vacua with the MSSM as the low energy effective theory. Here, one expects a statistical selection favoring large soft SUSY breaking terms leading to a derived value of the weak scale in each pocket universe (with appropriate electroweak symmetry breaking) which differs from the weak scale as measured in our universe. In contrast, the SUSY preserving μparameter is selected uniformly on a log scale as is consistent with the distribution of SM fermion masses: this favors smaller values of μ. An anthropic selection of the weak scale to within a factor of a few of our measured value -- in order to produce complex nuclei as we know them (atomic principle) -- provides statistical predictions for Higgs and sparticle masses in accord with LHC measurements. The statistical selection then more often leads to (radiatively-driven) {\it natural} SUSY models over the Standard Model or finely-tuned SUSY models such as mSUGRA/CMSSM, split, mini-split, spread, high scale or PeV SUSY. The predicted Higgs and superparticle spectra might be testable at HL-LHC via higgsino pair production but is certainly testable at higher energy hadron colliders with \sqrt{s}~ 30-100 TeV.

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arXiv2022

Detecting Heavy Higgs Bosons from Natural SUSY at a 100 TeV Hadron Collider

Supersymmetric models with radiatively-driven naturalness (RNS) enjoy low electroweak fine-tuning whilst respecting LHC search limits on gluinos and top squarks and allowing for $m_h\simeq 125$ GeV. While the heavier Higgs bosons $H,\ A$ may have TeV-scale masses, the SUSY conserving $μ$ parameter must lie in the few hundred GeV range. Thus, in natural SUSY models there should occur large heavy Higgs boson branching fractions to electroweakinos, with Higgs boson decays to higgsino plus gaugino dominating when they are kinematically accessible. These SUSY decays can open up new avenues for discovery. We investigate the prospects of discovering heavy neutral Higgs bosons $H$ and $A$ decaying into light plus heavy chargino pairs which can yield a four isolated lepton plus missing transverse energy signature at the LHC and at a future 100 TeV $pp$ collider. We find that discovery of heavy Higgs decay to electroweakinos via its $4\ell$ decay mode is very difficult at HL-LHC. For FCC-hh or SPPC, we study the $H,\ A \to $ SUSY reaction along with dominant physics backgrounds from the Standard Model and devise suitable selection requirements to extract a clean signal for FCC-hh or SPPC with $\sqrt{s}=100$ TeV, assuming an integrated luminosity of 15 $ab^{-1}$. We find that while a conventional cut-and-count analysis yields a signal statistical significance greater than $5σ$ for $m_{A,H}\sim 1.1-1.65$ TeV, a boosted-decision-tree analysis allows for heavy Higgs signal discovery at FCC-hh or SPPC for $m_{A,H}\sim 1-2$ TeV.

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arXiv2022

New angular (and other) cuts to improve the higgsino signal at the LHC

Motivated by the fact that naturalness arguments strongly suggest that the SUSY-preserving higgsino mass parameter mu cannot be too far above the weak scale, we re-examine higgsino pair production in association with a hard QCD jet at the HL-LHC. We focus on \ell^+\ell^-+\eslt+j events from the production and subsequent decay, \tchi_2^0\to\tchi_1^0\ell^+\ell^-, of the heavier neutral higgsino. The novel feature of our analysis is that we suggest angular cuts to reduce the important background from Z(\to ττ)+j events more efficiently than the m_{ττ}^2<0 cut that has been used by the ATLAS and CMS collaborations. Other cuts, needed to reduce backgrounds from t\bar{t}, WWj and W/Z+\ell\bar{\ell} production, are also delineated. We plot out the reach of LHC14 for 300 and 3000~fb^{-1} and also show distributions that serve to characterize the higgsino signal, noting that higgsinos may well be the only superpartners accessible at LHC14 in a well-motivated class of natural SUSY models.

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arXiv2022

On dark radiation from string moduli decay to ALPs

We examine the issue of dark radiation (DR) from string moduli decay into axion-like particles (ALPs). In KKLT-type models of moduli stabilization, the axionlike phases of moduli fields are expected to decouple whilst in LVS-type moduli stabilization some can remain light and may constitute dark radiation. We evaluate modulus decay to Minimal Supersymmetric Standard Model (MSSM) particles and dark radiation for more general compactifications. In spite of tightening error bars on ΔN_{eff}, we find only mild constraints on modulus-ALP couplings due to the somewhat suppressed modulus branching fraction to DR owing to the large number of MSSM decay modes. We anticipate that future CMB experiments with greater precision on ΔN_{eff} may still turn up evidence for DR if the ALP associated with the lightest modulus field is indeed light.

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