The Principle of Naturalness of small parameters of a theory is reviewed. While quantum field theories constructed from gauge fields and fermions only are natural, those containing elementary scalar fields are not. In particular the Higgs boson mass in the Standard Model of electro-weak forces is not stable against radiative corrections. Two old canonical solutions of this problem are: (i) where the Higgs boson is a fermion-antifermion composite (technicolour solution) or otherwise (ii) we need supersymmetry to protect the mass of elementary Higgs boson from possible large radiative corrections. In recent years some other mechanisms for electroweak symmetry breaking have been under intense investigation. These include the little Higgs models and the gauge-Higgs unification models where the Higgs boson is the zero mode of the extra-dimensional component of a higher dimensional gauge field. Naturalness issues of such models are also briefly reviewed.
The question of naturalness is addressed in the context of gauge-mediated supersymmetry breaking models. Requiring that $M_Z$ arises naturally imposes upper limits on the right-handed selectron mass in these models that are stronger than in the Minimal Supersymmetric Standard Model and are interesting from the point of view of searches at the current and future colliders.
We argue that the study of the statistics of the landscape of string vacua provides the first potentially predictive -- and also falsifiable -- framework for string theory. The question of whether the theory does or does not predict low energy supersymmetry breaking may well be the most accessible to analysis. We argue that low energy -- possibly very low energy -- supersymmetry breaking is likely to emerge, and enumerate questions which must be answered in order to make a definitive prediction.
We investigate spontaneous global symmetry breaking in the absence of Lorentz invariance, and study technical Naturalness of Nambu-Goldstone (NG) modes whose dispersion relation exhibits a hierarchy of multicritical phenomena with Lifshitz scaling and dynamical exponents $z>1$. For example, we find NG modes with a technically natural quadratic dispersion relation which do not break time reversal symmetry and are associated with a single broken symmetry generator, not a pair. The mechanism is protected by an enhanced `polynomial shift' symmetry in the free-field limit.
We give an intuitive proof of a new non-renormalization theorem in supersymmetric field theories. It applies both perturbatively and non-perturbatively. The superpotential is not renormalized in perturbation theory but receives non-perturbative corrections. However, these non-perturbative corrections are {\it not} generic functions of the fields consistent with the symmetries. Certain invariant terms are not generated. This violation of naturalness has applications to dynamical supersymmetry breaking.
We consider a supersymmetric SO(10) model which remains renormalisable upto Planck scale. The cosmology of such a model passes through a Left-Right symmetric phase. Potential problems associated with domain walls can be evaded if parity breaking is induced by soft terms when supersymmetry breaks in the hidden sector. The smallness of this breaking permits a brief period of domination by the domain walls ensuring dilution of gravitinos and other unwanted relics. The requirement that domain walls disappear constrains some of the soft parameters of the Higgs potential.
The gauge model with $SO(3)_{F}$ flavor symmetry and three Higgs triplets is studied. We show how the intriguing nearly degenerate neutrino mass and bi-maximal mixing scenario comes out naturally after spontaneous breaking of the symmetry. The hierarchy between the neutrino mass-squared differences, which is needed for reconciling both solar and atmospheric neutrino data, is naturally resulted from an approximate permutation symmetry. The model can also lead to interesting phenomena on lepton-flavor violations via the $SO(3)_{F}$ gauge interactions.
We study the mass of the lightest CP-even Higgs boson in the deflected mirage mediation that is a quite general framework of the mediation of supersymmetry breaking, incorporating the case where all of the modulus-, the anomaly- and the gauge-mediated contributions to the soft supersymmetry breaking parameters become sizable. We evaluate the degree of tuning the so-called mu parameter required for realizing a correct electroweak symmetry breaking and study how to accomplish both the observed Higgs boson mass and the relaxed fine-tuning. We identify the parameter space favored from such a persp…
We analyze the symmetry-breaking patterns of grand unified theories from the point of view of a recently-proposed criterion of renormalization-group naturalness. We perform the analysis on simple non-SUSY SU(5) and SO(10) and SUSY SU(5) GUTs. We find that the naturalness criterion can favor spontaneous-symmetry-breaking in the direction of the smallest of the maximal little groups. Some differences between theories with and without supersymmetry are also emphasized.
In MSSM models with various boundary conditions for the soft breaking terms (m_{soft}) and for a higgs mass of 126 GeV, there is a (minimal) electroweak fine-tuning Delta\approx 800 to 1000 for the constrained MSSM and Delta\approx 500 for non-universal gaugino masses. These values, often regarded as unacceptably large, may indicate a problem of supersymmetry (SUSY) breaking, rather than of SUSY itself. A minimal modification of these models is to lower the SUSY breaking scale in the hidden sector (\sqrt f) to few TeV, which we show to restore naturalness to more acceptable levels Delta\approx…
Models with dynamical supersymmetry breaking have the potential to solve many of the naturalness problems of hidden sector supergravity models. We review the argument that in a generic supergravity theory in which supersymmetry is {\it dynamically} broken in the hidden sector, only tiny Majorana masses for gauginos are generated. This situation is similar to that of theories with continuous R-symmetries, for which Hall and Randall have suggested that gluino masses could arise through mixings with an octet of chiral fields. We note that in hidden sector models, such mixing can only occur if the…
In order to significantly reduce the fine-tuning associated with the electroweak symmetry breaking in the minimal supersymmetric standard model (MSSM), we consider not only the minimal gravity mediation effects but also the minimal gauge mediation ones for a common supersymmetry breaking source at a hidden sector. In this "Minimal Mixed Mediation model," the minimal forms for the Kahler potential and the gauge kinetic function are employed at tree level. The MSSM gaugino masses are radiatively generated through the gauge mediation. Since a "focus point" of the soft Higgs mass parameter, m_{h_u…
Postulating that the NMSSM singlet is a meson of a microscopic confining theory opens up new model-building possibilities. Based on this, we construct calculable models of direct mediation that solve the mu/Bmu problem and simultaneously lead to realistic phenomenology. The singlet that couples to the Higgs fields develops a runaway produced by soft interactions, then stabilized by a small superpotential perturbation. The mechanism is first realized in an O'Raifeartaigh model of direct gauge mediation with metastable supersymmetry breaking. Focusing then on the microscopic theory, we argue tha…
We build a minimal neutral naturalness model in which the top partners are not charged under QCD, with a pseudo Goldstone Higgs arising from $SO(5)/SO(4)$ breaking. The color-neutral top partners generate the Higgs potential radiatively without quadratic divergence. The misalignment between the electroweak scale and global symmetry breaking scale is naturally obtained from suppression of the Higgs quadratic term, due to cancellation between singlet and doublet top partner contributions. This model can be embedded into ultraviolet holographic setup in composite Higgs framework, which even reali…
The absence of any signal of supersymmetry (SUSY) at the LHC has raised the SUSY particle mass scale compared to $Z$ boson mass $M_Z$. We investigate the naturalness of the electroweak symmetry breaking after considering radiative symmetry breaking along with 125 GeV Higgs mass. We find that the important quantity to measure the naturalness of the hierarchy between the SUSY scale and $M_Z$ is the separation between the radiative symmetry breaking scale, i.e., where $m_{H_u}^2+μ^2$ turns negative for large $\tanβ$ case ($μ$ is the Higgsino mass and $m_{H_u}$ is the SUSY breaking up-type Higgs b…
The notion of stringy naturalness-- that an observable O_2 is more natural than O_1 if more (phenomenologically acceptable) vacua solutions lead to O_2 rather than O_1-- is examined within the context of the Standard Model (SM) and various SUSY extensions: CMSSM/mSUGRA, high-scale SUSY and radiatively-driven natural SUSY (RNS). Rather general arguments from string theory suggest a (possibly mild) statistical draw towards vacua with large soft SUSY breaking terms. These vacua must be tempered by an anthropic veto of non-standard vacua or vacua with too large a value of the weak scale m(weak). W…
With the Higgs boson discovery and no new physics found at the LHC, confidence in Naturalness as a guiding principle for particle physics is under increased pressure. We wait to see if it proves its mettle in the LHC upgrades ahead, and beyond. In the meantime, in a series of "realistic intellectual leaps" I present a justification {\it a posteriori} of the Naturalness criterion by suggesting that uncompromising application of the principle to quantum electrodynamics leads toward the Standard Model and Higgs boson without additional experimental input. Potential lessons for today and future th…
We propose a model of a confining dark sector, dark technicolor, that communicates with the Standard Model through the Higgs portal. In this model electroweak symmetry breaking and dark matter share a common origin, and the electroweak scale is generated dynamically. Our motivation to suggest this model is the absense of evidence for new physics from recent LHC data. Although the conclusion is far from certain at this point, this lack of evidence may suggest that no mechanism exists at the electroweak scale to stabilise the Higgs mass against radiative corrections from UV physics. The usual re…
Weak scale supersymmetric theories often suffer from several naturalness problems: the problems of reproducing the correct scale for electroweak symmetry breaking, the correct abundance for dark matter, and small rates for flavor violating processes. We argue that the first two problems point to particular regions of parameter space in models with weak scale supersymmetry: those with a small mu term. This has an interesting implication on direct dark matter detection experiments. We find that, if the signs of the three gaugino mass parameters are all equal, we can obtain a solid lower bound on…
A Higgs boson mass $\sim 126$ GeV as determined by the LHC data requires a large loop correction which in turn implies a large sfermion mass. Implication of this result for the stability of the proton in supersymmetric grand unified theories is examined including other experiments constraints along with the most recent result on cold dark matter from Planck. It is shown that over the allowed parameter space of supergravity unified models, proton lifetime is highly sensitive to the Higgs boson mass and a few GeV shift in its mass can change the proton decay lifetime for the mode $p\to \bar νK^+…
Anomaly-mediated supersymmetry breaking (AMSB) models seem to have become increasingly implausible due to 1. difficulty in generating a Higgs mass m(h)~125 GeV, 2. typically unnatural superparticle spectra characterized by a large superpotential mu term and 3. the possibility of a wino-like lightest SUSY particle (LSP) as dark matter now seems to be excluded. In the present paper we propose some minor modifications to the paradigm model which solve these three issues. Instead of adding a universal bulk scalar mass to avoid tachyonic sleptons, we add distinct Higgs and matter scalar soft masses…
In this paper we study a new class of supersymmetric models that can explain a 125 GeV Higgs without fine-tuning. These models contain additional `auxiliary Higgs' fields with large tree-level quartic interaction terms but no Yukawa couplings. These have electroweak-breaking vacuum expectation values, and contribute to the VEVs of the MSSM Higgs fields either through an induced quartic or through an induced tadpole. The quartic interactions for the auxiliary Higgs fields can arise from either D-terms or F-terms. The tadpole mechanism has been previously studied in strongly-coupled models with …
We present a supersymmetric model of electroweak symmetry-breaking exhibiting improved naturalness, wherein the stop mass can be pushed beyond the reach of the Large Hadron Collider without unnatural fine tuning. This implies that supersymmetry may still solve the hierarchy problem, even if it eludes detection at the LHC.
We study the fine tuning in the parameter space of the semi-constrained NMSSM, where most soft Susy breaking parameters are universal at the GUT scale. We discuss the dependence of the fine tuning on the soft Susy breaking parameters M_1/2 and m0, and on the Higgs masses in NMSSM specific scenarios involving large singlet-doublet Higgs mixing or dominant Higgs-to-Higgs decays. Whereas these latter scenarios allow a priori for considerably less fine tuning than the constrained MSSM, the early LHC results rule out a large part of the parameter space of the semi-constrained NMSSM corresponding to…
Many models of electroweak symmetry-breaking with an extended Higgs sector exhibit improved naturalness, wherein the new physics scale, at which quadratic divergences of Higgs mass parameters due to top quark loops are cut off, can be pushed beyond the reach of the Large Hadron Collider without unnatural fine tuning. Such models include examples where the new physics is supersymmetry, implying that supersymmetry may still solve the hierarchy problem, even if it eludes detection at the LHC.
Supersymmetry solves the gauge hierarchy problem of the Standard Model if the masses of supersymmetric partners of the SM particles are close to the weak scale. In this thesis, we argue that the supersymmetric Standard Model, while avoiding the fine tuning in electroweak symmetry breaking, requires unnaturalness/fine tuning in some (other) sector of the theory. For example, Baryon and Lepton number violating operators are allowed which lead to proton decay and flavor changing neutral currents. We study some of the constraints from the latter in this thesis. We have to impose an R-parity for th…
Extending the spacetime symmetries of standard model (SM) by scale invariance (SI) may address the Higgs naturalness problem. In this article we attempt to embed accidental dark matter (DM) into SISM, requiring that the symmetry protecting DM stability is accidental due to the model structure rather than imposed by hand. In this framework, if the light SM-like Higgs boson is the pseudo Goldstone boson of SI spontaneously breaking, we can even pine down the model, two-Higgs-doublets plus a real singlet: The singlet is the DM candidate and the extra Higgs doublet triggers electroweak symmetry br…
The discovery of a 125 GeV Higgs boson and rising lower bounds on the masses of superpartners have lead to concerns that supersymmetric models are now fine tuned. Large stop masses, required for a 125 GeV Higgs, feed into the electroweak symmetry breaking conditions through renormalisation group equations forcing one to fine tune these parameters to obtain the correct electroweak vacuum expectation value. Nonetheless this fine tuning depends crucially on our assumptions about the supersymmetry breaking scale. At the same time $U(1)$ extensions provide the most compelling solution to the $μ$-pr…
We derive constraints on combinations of O(p^6) chiral coupling constants by matching a recent two-loop calculation of the pi-K scattering amplitude with a set of sum rules. We examine the validity of the natural expectation that the values of the chiral couplings can be associated with physics properties of the light resonance sector. We focus, in particular, on flavour symmetry breaking of vector resonances. A resonance chiral Lagrangian is constructed which incorporates flavour symmetry breaking more completely than was done before. We use pi-K unsubtracted sum rules as tests of the modelli…
We show that the electroweak fine-tuning parameter Δ_{\rm EW} derived from the well-known electroweak symmetry breaking condition written in terms of weak scale parameters leads to {\it a bound on fine-tuning in the MSSM} and explain its utility for phenomenological analyses. We argue that a small magnitude of the mu parameter, and the concomitant presence of light higgsinos, is the most basic consequence of naturalness in SUSY models, and list the resulting implications of this for experiments at the LHC and at future e^+e^- colliders.
It has been suggested that electroweak symmetry breaking in the Standard Model may be natural if the Standard Model merges into a conformal field theory (CFT) at short distances. In such a scenario the Higgs mass would be protected from quantum corrections by the scale invariance of the CFT. In order for the Standard Model to merge into a CFT at least one new ultraviolet (UV) scale is required at which the couplings turn over from their usual Standard Model running to the fixed point behavior. We argue that the Higgs mass is sensitive to such a turn-over scale even if there are no associated m…
We study a holographic realisation of a composite Higgs model with an SO(6)/SO(5) symmetry breaking coset in which the top sector includes colour-neutral twin-partners that reduce the sensitivity of the Higgs mass to the cut-off. Key to this neutral-naturalness mechanism is a Z2 symmetry that leaves the Yukawa couplings to the Higgs boson invariant under an exchange of the top quark and twin top quark, but the symmetry structure of the model means that the Z2 symmetry is not present in the gauge boson couplings to the Higgs. Within the calculable framework of holography we construct and study …
Naturalness of electroweak symmetry breaking in the next-to-minimal supersymmetric model points to scenarios in which the lightest CP-even Higgs boson has SM-like ZZh coupling and mass m_h ~ 100 GeV and decays partly via h -> b \bar b but dominantly into two CP-odd Higgs bosons, h -> aa, where m_a < 2m_b so that a -> tau+ tau- (or light quarks and gluons) decays are dominant. These preferred scenarios correlate well with the observed excess of events at LEP for m_h ~ 100 GeV.
Introducing a source for a bi-local composite operator motivated by the perturbative expansion in gauge couplings, we calculate its effective potential in the renormalization group of Standard Model with no involvement of technicolor. The potential indicates the breaking of electroweak symmetry below a scale M due to a nonzero vacuum expectation value of neutral component for the SU(2)-doublet operator. At virtualities below a cut off Λwe introduce the local higgs approximation for the effective fields of sources coupled to the composite operators. The value of Λ\approx 600 GeV is fixed by the…
It is pointed out that in supersymmetric models with a new gauge symmetry under which the Higgs is charged, the fine-tuning of the electroweak symmetry breaking is relaxed due to suppression of the top Yukawa coupling at higher scales by a new large gauge coupling. We calculate the fine-tuning in an explicit model and find that the lower bounds on stops and gluino masses from the naturalness criterion are increased by several hundred GeV in comparison to the Minimal Supersymmetric Standard Model (MSSM). The fine-tuning is improved by one to two orders of magnitude as compared to the MSSM, as a…
We outline a scenario where both the Higgs and a complex scalar dark matter candidate arise as the pseudo-Nambu-Goldstone bosons of breaking a global $SO(7)$ symmetry to $SO(6)$. The novelty of our construction is that the symmetry partners of the Standard Model top-quark are charged under a hidden color group and not the usual $SU(3)_c$. Consequently, the scale of spontaneous symmetry breaking and the masses of the top partners can be significantly lower than those with colored top partners. Taking these scales to be lower at once makes the model more natural and also reduces the induced non-…
We study classically scale invariant models in which the Standard Model Higgs mass term is replaced in the Lagrangian by a Higgs portal coupling to a complex scalar field of a dark sector. We focus on models that are weakly coupled with the quartic scalar couplings nearly vanishing at the Planck scale. The dark sector contains fermions and scalars charged under dark SU(2) x U(1) gauge interactions. Radiative breaking of the dark gauge group triggers electroweak symmetry breaking through the Higgs portal coupling. Requiring both a Higgs boson mass of 125.5 GeV and stability of the Higgs potenti…
We analyse the fine-tuning constraints arising from absence of superpartners at LEP, without strong universality assumptions. We show that such constraints do not imply that charginos or neutralinos should have been seen at LEP, contrary to the usual arguments. They do however imply relatively light gluinos $(m_{\tilde g} \lsim 350 GeV)$ and/or a relation between the soft-breaking SU(3) gaugino mass and Higgs soft mass $m_{H_U}$. The LEP limit on the Higgs mass is significant, especially at low $\tan β$, and we investigate to what extent this provides evidence for both a lighter gluino and cor…
Solutions to the electroweak hierarchy problem typically introduce a new symmetry to stabilize the quadratic ultraviolet sensitivity in the self-energy of the Higgs boson. The new symmetry is either broken softly or collectively, as for example in supersymmetric and little Higgs theories. At low energies such theories contain naturalness partners of the Standard Model fields which are responsible for canceling the quadratic divergence in the squared Higgs mass. Post the discovery of any partner-like particles, we propose to test the aforementioned cancellation by measuring relevant Higgs coupl…
If weak scale supersymmetry (SUSY) is to somehow explain the radiative stability of the Higgs boson mass, it is likely that non-minimal variants of SUSY models should be considered. Under the assumption that the dark matter of the universe is comprised of neutralinos, recent limits from direct detection experiments as well as dark matter abundance measurements place stringent bounds on the naturalness of minimal supersymmetric models. We show that even non-minimal models introducing moderately decoupled new physics in order to address the Higgs boson mass problem face similar issues, with one …
The natural cutoff scale for the quadratically divergent top quark contribution to the Higgs mass parameter can be significantly raised above the surprisingly low standard model value, with important consequences for the LHC: the physics that cancels the top quark divergence may be out of reach, while an electroweak sector with "improved naturalness" may be discovered. Such a sector, consistent with electroweak precision tests, arises in the two Higgs doublet model with heavy Higgs and top quark interactions that approach strong coupling.
Common lore has it that naturalness of electroweak breaking in the SM requires new physics (NP) at Lambda < 2-3 TeV, hopefully within the reach of LHC. Moreover the Higgs should be light (m_h < 219 GeV) to pass electroweak precision tests (EWPT). However one should be prepared for "unexpected" (although admittedly unpleasant) results at LHC, i.e. no NP and/or a heavy Higgs. We revisit recent attempts to accommodate this by modifying the SM Higgs sector (using 2-Higgs-doublet models). We find that these models do not improve the naturalness of the SM, and so they do not change the expectations …
Inspired by the possibility of high-scale supersymmetry breaking in the string landscape where the cosmological constant problem and the gauge hierarchy problem can be solved while the strong CP problem is still a challenge for naturalness, we propose a supersymmetric KSVZ axion model with an approximate universal intermediate-scale ($\sim 10^{11}$ GeV) supersymmetry breaking. To protect the global Peccei--Quinn (PQ) symmetry against quantum gravitational violation, we consider the gauged discrete $Z_N$ PQ symmetry. In our model the axion can be a cold dark matter candidate, and the intermedia…
The weak gravity conjecture (WGC) is an ultraviolet consistency condition asserting that an Abelian force requires a state of charge $q$ and mass $m$ with $q>m/m_{\rm Pl}$. We generalize the WGC to product gauge groups and study its tension with the naturalness principle for a charged scalar coupled to gravity. Reconciling naturalness with the WGC either requires a Higgs phase or a low cutoff at $Λ\sim q m_{\rm Pl}$. If neither applies, one can construct simple models that forbid a natural electroweak scale and whose observation would rule out the naturalness principle.
With a bottom-up approach, we consider naturalness in the MSSM and NMSSM. Assuming the light stops, the LHC gluino search implies that the degree of fine tuning in both models is less than 2.5%. Taking the LHC hints for the SM-like Higgs boson mass m_h\sim125 GeV seriously, we find that naturalness will favor the NMSSM. We study the Higgs boson mass for several scenarios in the NMSSM: (1) A large λand the doublet-singlet Higgs boson mixing effect pushing upward or pulling downward m_h. The former case can readily give the di-photon excess of the Higgs boson decay whereas the latter case can no…
The Higgs sector in neutral naturalness models provides a portal to the hidden sectors, and thus measurements of Higgs couplings at current and future colliders play a central role in constraining the parameter space of the model. We investigate a class of neutral naturalness models, in which the Higgs boson is a pseudo-Goldstone boson from the universal SO(N)/SO(N-1) coset structure. Integrating out the radial mode from the spontaneous global symmetry breaking, we obtain various dimension-six operators in the Standard Model effective field theory, and calculate the low energy Higgs effective …
The Higgs mass implies fine-tuning for minimal theories of weak scale supersymmetry (SUSY). Non-decoupling effects can boost the Higgs mass when new states interact with the Higgs, but new sources of SUSY breaking that accompany such extensions threaten naturalness. We show that two singlets with a Dirac mass can increase the Higgs mass while maintaining naturalness in the presence of large SUSY breaking in the singlet sector. We explore the modified Higgs phenomenology of this scenario, which we call the "Dirac NMSSM."
We show that naturalness of the weak scale can be comfortably reconciled with both LHC null results and observed Higgs properties provided the double protection of supersymmetry and the twin Higgs mechanism. This double protection radically alters conventional signs of naturalness at the LHC while respecting gauge coupling unification and precision electroweak limits. We find the measured Higgs mass, couplings, and percent-level naturalness of the weak scale are compatible with stops at ~3.5 TeV and higgsinos at ~1 TeV. The primary signs of naturalness in this scenario include modifications of…
The Gell-Mann-Levy (GML), Schwinger and Standard Models were previously shown to lack a Brout-Englert-Higgs (BEH) fine-tuning problem due to quadratic divergences, with finite Euclidean cut-off Λ, because of the symmetries obeyed by all O(Λ^2) contributions. We extend those results to finite contributions from certain M_{Heavy}^2>> m_{BEH}^2 particles in SO(2) versions of GML and Schwinger. We demonstrate explicit 1-loop physical naturalness for two SO(2) singlet examples: a heavy real scalar S and a right-handed Type 1 see-saw Majorana neutrino. We prove that for low |q^2| the heavy degrees o…
Naturalness demands that the quadratic divergence of the one-loop top contribution to the Higgs mass be cancelled at a scale below 1 TeV. This can be achieved by introducing a fermionic (spin-1/2) top partner, as in, for example, Little Higgs models. In this paper, we study the phenomenology of a simple model realizing this mechanism. We present the current bounds on the model from precision electroweak fits, flavor physics, and direct searches at the LHC. The lower bound on the top partner mass from precision electroweak data is approximately 500 GeV, while the LHC bound with 5/fb of data at …
Free massless scalars have a shift symmetry. This is usually broken by gauge and Yukawa interactions, such that quantum corrections induce a quadratically divergent mass term. In the Standard Model this leads to the hierarchy problem of the electroweak theory, the question why the Higgs mass is so much smaller than the Planck mass. We present an example where a large scalar mass term is avoided by coupling the scalar to an infinite tower of massive states which are obtained from a six-dimensional theory compactified on a torus with magnetic flux. The series of divergent quantum corrections add…
We study the contributions of supersymmetric models with a $U(1)$ horizontal symmetry and only spontaneous CP breaking to various lepton flavor observables, such as $μ\to eγ$ and the electron electric dipole moment. We show that both a horizontal symmetry and a lack of explicit CP violation can alleviate the existing bounds from such observables. The undetermined $\mathcal{O}(1)$ coefficients in such mass matrix models muddle the interpretation of the bounds from various flavor observables. To overcome this, we define a new fine-tuning measure for different observables in such setups. This all…
We study models of gauge-mediated supersymmetry breaking with messengers that do not belong to complete representations of grand-unified gauge groups. We show that certain setups characterized by heavy Wino can greatly improve the fine tuning with respect to models with unified messengers, such as minimal gauge mediation. The typical models with low tuning feature multi-TeV superparticles, with the exception of the Higgsinos and possibly Bino and right-handed sleptons. As a consequence, the absence of signals for supersymmetry at the LHC is trivially accommodated in our framework. On the other…
We discuss how naturalness predicts the scale of new physics. Two conditions on the scale are considered. The first is the more conservative condition due to Veltman (Acta Phys. Polon. B 12, 437 (1981)). It requires that radiative corrections to the electroweak mass scale would be reasonably small. The second is the condition due to Barbieri and Giudice (Nucl. Phys. B 306, 63 (1988)), which is more popular lately. It requires that physical mass scale would not be oversensitive to the values of the input parameters. We show here that the above two conditions behave differently if higher order c…
We analyse the naturalness of the Minimal Supersymmetric Standard Model (MSSM) in the light of recent LHC results from the ATLAS and CMS experiments. We study non-universal boundary conditions for the scalar and the gaugino sector, with fixed relations between some of the soft breaking parameters, and find a significant reduction of fine-tuning for non-universal gaugino masses. For a Higgs mass of about 125 GeV, as observed recently, we find parameter regions with a fine-tuning of O(10), taking into account experimental and theoretical uncertainties. These regions also survive after comparison…
Mirage mediation realized in the Kachru-Kallosh-Linde-Trivedi (KKLT) flux compactification can naturally suppress the up-type Higgs soft mass at low energy scales. As a result, compared to the conventional scenarios, the degree of electroweak fine-tuning can be reduced further up to by a loop factor if the Higgsinos are much lighter than the heavy Higgs doublet. Interestingly, this feature holds even in high-scale supersymmetry as long as the gauge coupling unification, which is required as a prerequisite for mirage mediation, accommodates such light Higgsinos. Under the experimental constrain…
The relationship between the degree of fine-tuning in Electroweak Symmetry Breaking (EWSB) and the discoverability of dark matter in current and next generation direct detection experiments is investigated in the context of two unified Supersymmetry scenarios: the constrained Minimal Supersymmetric Standard Model (CMSSM) and models with non-universal Higgs masses (NUHM). Attention is drawn to the mechanism(s) by which the relic abundance of neutralino dark matter is suppressed to cosmologically viable values. After a summary of Amsel, Freese, and Sandick (2011), results are updated to reflect …
