The recent measurement of the muon anomalous magnetic moment aμ≡(g−2)μ/2 by the Fermilab Muon g−2 experiment sharpens an earlier discrepancy between theory and the BNL E821 experiment. We examine the ...predicted Δaμ≡aμ(exp)−aμ(th) in the context of supersymmetry with low electroweak naturalness (restricting to models which give a plausible explanation for the magnitude of the weak scale). A global analysis including LHC Higgs mass and sparticle search limits points to interpretation within the normal scalar mass hierarchy (NSMH) SUSY model wherein first/second generation matter scalars are much lighter than third generation scalars. We present a benchmark model for a viable NSMH point which is natural, obeys LHC Higgs and sparticle mass constraints and explains the muon magnetic anomaly. Aside from NSMH models, then we find the (g−2)μ anomaly cannot be explained within the context of natural SUSY, where a variety of data point to decoupled first/second generation scalars. The situation is worse within the string landscape where first/second generation matter scalars are pulled to values in the 10−50 TeV range. An alternative interpretation for SUSY models with decoupled scalar masses is that perhaps the recent lattice evaluation of the hadronic vacuum polarization could be confirmed which leads to a Standard Model theory-experiment agreement in which case there is no anomaly.
Is natural higgsino-only dark matter excluded? Baer, Howard; Barger, Vernon; Sengupta, Dibyashree ...
The European physical journal. C, Particles and fields,
10/2018, Volume:
78, Issue:
10
Journal Article
Peer reviewed
Open access
The requirement of electroweak naturalness in supersymmetric (SUSY) models of particle physics necessitates light higgsinos not too far from the weak scale characterized by
m
weak
∼
m
W
,
Z
,
h
∼
100
...GeV
. On the other hand, LHC Higgs mass measurements and sparticle mass limits point to a SUSY breaking scale in the multi-TeV regime. Under such conditions, the lightest SUSY particle is expected to be a mainly higgsino-like neutralino with non-negligible gaugino components (required by naturalness). The computed thermal WIMP abundance in natural SUSY models is then found to be typically a factor 5–20 below its measured value. To gain concordance with observations, either an additional DM particle (the axion is a well-motivated possibility) must be present or additional non-thermal mechanisms must augment the neutralino abundance. We compare present direct and indirect WIMP detection limits to three natural SUSY models based on gravity-, anomaly- and mirage-mediation. We show that the case of natural higgsino-only dark matter where non-thermal production mechanisms augment its relic density, is essentially excluded by a combination of direct detection constraints from PandaX-II, LUX and Xenon-1t experiments, and by bounds from Fermi-LAT/MAGIC observations of gamma rays from dwarf spheroidal galaxies.
Models of natural supersymmetry give rise to a weak scale
m
weak
∼
m
W
,
Z
,
h
∼
100
GeV without any (implausible) finetuning of independent contributions to the weak scale. These models, which ...exhibit radiatively driven naturalness (RNS), are expected to arise from statistical analysis of the string landscape wherein large soft terms are favored, but subject to a not-too-large value of the derived weak scale in each pocket universe of the greater multiverse. The string landscape picture then predicts, using the Isajet SUSY spectra generator Isasugra, a statistical peak at
m
h
∼
125
GeV with sparticles generally beyond current LHC search limits. In this paper, we investigate how well these conclusions hold up using other popular spectra generators: SOFTSUSY, SPHENO and SUSPECT (SSS). We built a computer code DEW4SLHA which operates on SUSY Les Houches Accord files to calculate the associated electroweak naturalness measure
Δ
EW
. The SSS generators tend to yield a Higgs mass peak
∼
125
–127 GeV with a superparticle mass spectra rather similar to that generated by Isasugra. In an Appendix, we include loop corrections to
Δ
EW
in a more standard notation.
A
bstract
Predictions for the scale of SUSY breaking from the string landscape go back at least a decade to the work of Denef and Douglas on the statistics of flux vacua. The assumption that an ...assortment of SUSY breaking
F
and
D
terms are present in the hidden sector, and their values are uniformly distributed in the landscape of
D
= 4,
N
= 1 effective supergravity models, leads to the expectation that the landscape pulls towards large values of soft terms favored by a power law behavior
P
(
m
soft
) ∼
m
soft
n
. On the other hand, similar to Weinberg’s prediction of the cosmological constant, one can assume an anthropic selection of weak scales not too far from the measured value characterized by
m
W,Z,h
∼ 100 GeV. Working within a fertile patch of gravity-mediated low energy effective theories where the superpotential
μ
term is ≪
m
3/2
, as occurs in models such as radiative breaking of Peccei-Quinn symmetry, this biases statistical distributions on the landscape by a cutoff on the parameter Δ
EW
, which measures fine-tuning in the
m
Z
-
μ
mass relation. The combined effect of statistical and anthropic pulls turns out to favor low energy phenomenology that is more or less agnostic to UV physics. While a uniform selection
n
= 0 of soft terms produces too low a value for
m
h
, taking
n
= 1 and 2 produce most probabilistically
m
h
∼ 125 GeV for negative trilinear terms. For
n
≥ 1, there is a pull towards split generations with
m
q
˜
,
ℓ
˜
1
2
∼
10
−
30
TeV whilst
m
t
˜
1
∼
1
−
2
T
e
V
.
The most probable gluino mass comes in at ∼ 3 − 4 TeV — apparently beyond the reach of HL-LHC (although the required quasi-degenerate higgsinos should still be within reach). We comment on consequences for SUSY collider and dark matter searches.
Considerations from electroweak naturalness and stringy naturalness imply a little hierarchy in supersymmetric models where the superpotential higgsino mass parameter μ is of order the weak scale ...whilst the soft SUSY breaking terms may be in the (multi-) TeV range. In such a case, discovery of SUSY at LHC may be most likely in the higgsino pair production channel. Indeed, ATLAS and CMS are performing searches in the higgsino mass discovery plane of mχ˜20 vs. Δm0≡mχ˜20−mχ˜10. We examine several theoretical aspects of this discovery plane in both the gravity-mediation NUHM2 model and the general mirage-mediation (GMM′) models. These include: the associated chargino mass mχ˜1±, the expected regions of the bottom-up notion of electroweak naturalness ΔEW, and the expected regions of stringy naturalness. While compatibility with electroweak naturalness allows for mass gaps Δm0∼ 4-20 GeV, stringy naturalness exhibits a clear preference for yet smaller mass gaps of 4-10 GeV. For still smaller mass gaps, the plane becomes sharply unnatural since very large gaugino masses are required. This study informs the most promising SUSY search channels and parameter space regions for the upcoming HL-LHC runs and possible HE-LHC option.
A
bstract
While the SUSY flavor, CP and gravitino problems seem to favor a very heavy spectrum of matter scalars, fine-tuning in the electroweak sector prefers low values of superpotential mass μ. In ...the limit of low μ, the two lightest neutralinos and light chargino are higgsino-like. The light charginos and neutralinos may have large production cross sections at LHC, but since they are nearly mass degenerate, there is only small energy release in three-body sparticle decays. Possible dilepton and trilepton signatures are difficult to observe after mild cuts due to the very soft pT spectrum of the final state isolated leptons. Thus, the higgsino-world scenario can easily elude standard SUSY searches at the LHC. It should motivate experimental searches to focus on dimuon and trimuon production at the very lowest p
T
(
μ
) values possible. If the neutralino relic abundance is enhanced via non-standard cosmological dark matter production, then there exist excellent prospects for direct or indirect detection of higgsino-like WIMPs. While the higgsino-world scenario may easily hide from LHC SUSY searches, a linear e
+
e
−
collider or a muon collider operating in the
range would be able to easily access the chargino and neutralino pair production reactions.
The total cross section of the process μ−μ+→νμν¯μtt¯H has strong dependence on the CP phase ξ of the top Yukawa coupling, where the ratio of ξ=π and ξ=0 (SM) grows to 670 at s=30 TeV, 3400 at 100 ...TeV. We study the cause of the strong energy dependence and identify its origin as the (E/mW)2 growth of the weak boson fusion sub-amplitudes, WL−WL+→tt¯H, with the two W's are longitudinally polarized. We repeat the study in the SMEFT framework where EW gauge invariance is manifest and find that the highest energy cross section is reduced to a quarter of the complex top Yukawa model result, with the same energy power. By applying the Goldstone boson (GB) equivalence theorem, we identify the origin of this strong energy growth of the SMEFT amplitudes as associated with the dimension-6 π−π+ttH vertex, where π± denotes the GB of W±. We obtain the unitarity bound on the coefficient of the SMEFT operator by studying all 2→2 and 2→3 cross sections in the J=0 channel.
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