Stability Of Electroweak Vacuum Research Articles

Primordial Black Holes Are True Vacuum Nurseries

The Hawking evaporation of primordial black holes (PBH) reheats the Universe locally, forming hot spots that survive throughout their lifetime. We propose to use the temperature profile of such hot spots to calculate the decay rate of metastable vacua in cosmology, avoiding inconsistencies inherent to the Hartle-Hawking or Unruh vacuum. We apply our formalism to the case of the electroweak vacuum stability and find that a PBH energy fraction β>7×10−80(M/g)3/2 is ruled out for black holes with masses 0.8g<M<1015g.

The rise and fall of the Standard-Model Higgs: electroweak vacuum stability during kination

In this paper we investigate the vacuum stability of the non-minimally coupled Standard-Model Higgs during a phase of kinetic domination following the end of inflation. The non-minimal coupling to curvature stabilises the Higgs fluctuations during inflation while driving them towards the instability scale during kination, when they can classically overcome the potential barrier separating the false electroweak vacuum from the true one at super-Planckian field values. Avoiding the instability of the Standard-Model vacuum sets an upper bound on the inflationary scale that depends both on the strength of the non-minimal interaction and on the top quark Yukawa coupling. Classical vacuum stability is guaranteed if the gravitationally-produced energy density is smaller than the height of barrier in the effective potential. Interestingly enough, thanks to the explosive particle production in the tachyonic phase, the Higgs itself can be also appointed to the role of reheaton field responsible for the onset of the hot Big Bang era, setting an additional lower bound on the inflationary scale Hinf\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {\\mathcal{H}}_{\ extrm{inf}} $$\\end{document} ≳ 105.5 GeV. Overall, these constraints favour lower masses for the top quark, in agreement with the current measurements of the top quark pole mass. We perform our analysis semi-analytically in terms of the one-loop and three-loop running of the Standard-Model Higgs self-coupling and make use of lattice-based parametric formulas for studying the (re)heating phase derived in arXiv:2307.03774. For a specific choice of mt = 171.3 GeV we perform also an extensive numerical scanning of the parameter space via classical lattice simulations, identifying stable/unstable regions and supporting the previous analytical arguments. For this fiducial value, the heating of the Universe is achieved at temperatures in the range 10−2–109 GeV.

Stability of electroweak vacuum and supersymmetric contribution to muon g − 2

We study the stability of the electroweak vacuum in the supersymmetric (SUSY) standard model (SM), paying particular attention to its relation to the SUSY contribution to the muon anomalous magnetic moment aμ. If the SUSY contribution to aμ is sizable, the electroweak vacuum may become unstable because of enhanced trilinear scalar interactions. With aμ being fixed, larger slepton masses require more enhanced trilinear couplings, which make the electroweak vacuum more unstable. Thus, assuming SUSY contribution to aμ being sizable, an upper bound on the slepton masses is obtained. We give a detailed prescription to perform a full one-loop calculation of the decay rate of the electroweak vacuum for the case that the SUSY contribution to aμ is enhanced. We also give an upper bound on the slepton masses as a function of the SUSY contribution to aμ.

Modified hybrid inflation, reheating, and stabilization of the electroweak vacuum

We propose a modification to the standard hybrid inflation model \cite{Linde:1993cn}, that connects a successful hybrid inflation scenario to the standard model Higgs sector, via the electroweak vacuum stability. The proposed model results in an effective inflation potential of a hilltop-type, with both the trans-Planckian and sub-Planckian inflation regimes consistent with the recent Planck/BICEP combined results. Reheating via the inflation sector decays to right-handed neutrinos is considered. An upper bound on the reheating temperature $T_{\rm R} \lsim 2\times 10^{11}~(1\times 10^{13})$ GeV, for large~(small) field inflation, will suppress contributions from one-loop quantum corrections to the inflation potential. This may push the neutrino Yukawa couplings to be ${\cal O}(1)$ and affect the vacuum stability. We show that the couplings of the SM Higgs to the inflation sector can guarantee the electroweak vacuum stability up to the Planck scale. The so-called hybrid Higgs-inflaton model leads to a positive correction for the Higgs quartic coupling at a threshold scale, which is shown to have a very significant effect in stabilizing the electroweak vacuum. We find that even with ${\cal O}(1)$ neutrino Yukawa couplings, threshold corrections leave the SM vacuum stability intact.

Axionic Dirac seesaw mechanism and electroweak vacuum stability

We explore the connection between tree-level Dirac neutrino masses and axion physics in a scenario where the Peccei-Quinn (PQ) symmetry enforces lepton number conservation perturbatively. Requiring that the PQ scale ${f}_{a}$ is the only heavy scale to play a role in neutrino mass generation, we are led to the construction of a Kim--Shifman--Vainshtein--Zakharov-type model where Dirac neutrino masses are inversely proportional to ${f}_{a}$, provided a real scalar triplet (zero hypercharge) is added to the standard model scalar sector. We analyze this extended scalar sector, focusing on the stabilization of the electroweak vacuum. The contribution of the triplet vacuum expectation value to the $W$ mass may also be responsible for the recent hint of beyond-the-SM physics by the CDF collaboration.

The stability analysis of the extended singlet scalar model with two high scale minima

We study the simplest viable dark matter (DM) model with a real singlet scalar, vector-like singlet, and doublet fermions. The Yukawa couplings associated with the fermion sector are important in obtaining the current DM relic density through Freeze-out and Freeze-in mechanisms. In addition to the standard model-like high scale minima along the Higgs field, we find other high scale minima along the singlet scalar field direction. The other minima appears due to the renormalization group evolutions of the couplings involving the gauge sector, Higgs portal, and the new Yukawa sector. A detailed study of the parameter space identifying the region of electroweak vacuum stability and metastability along different directions of the scalar field is carried out using different phase diagrams.

Minimal dark matter model for muon g−2 with scalar lepton partners up to the TeV scale

The E989 experiment at the Fermi National Laboratory reported a $4.2\ensuremath{\sigma}$ discrepancy between the measured magnetic dipole moment of the muon, and its prediction in the Standard Model (SM). In this study, we address the anomaly by considering a minimal and generic extension to the SM which also provides for a dark matter (DM) candidate. The extra states in this framework are: a SM singlet Majorana fermion, referred to as the Bino, playing the role of DM; and muonic scalars, referred to as sleptons. The couplings between the sleptons, SM muons and the Bino can account for the muon $g\ensuremath{-}2$ anomaly if the scalar muon partners, or smuons, mix chirality. On the other hand, the DM relic density is satisfied primarily through coannihilation effects involving the Bino and the lighter sleptons. The viable parameter space of our model includes regions with relatively light coannihilating particles, similar to what has been found in previous scans of the Minimal Supersymmetric Standard Model (MSSM). Relaxing the assumption of minimal flavor violation typically assumed in the MSSM, we see that scenarios with sizable smuon mixing and large mass splittings between the smuons can satisfy both the muon $g\ensuremath{-}2$ anomaly and the DM relic density for coannihilating particle masses up to and beyond the TeV scale. When we specify the origin of the left-right smuon mixing to be trilinear couplings between the smuons and the SM Higgs boson, the constraints on these scenarios arising from perturbative unitarity and electroweak vacuum stability confine the coannihilating particle masses to be $\ensuremath{\lesssim}1\text{ }\text{ }\mathrm{TeV}$. We demonstrate that next generation direct detection experiments are only marginally sensitive to the viable parameter space of our model, and, thus, a future lepton collider could be the essential probe necessary to distinguish our model from other solutions to the muon $g\ensuremath{-}2$ anomaly which involve extra states beyond the SM.

SO(10) grand unification with minimal dark matter and color octet scalars

The minimal dark matter (MDM) scenario is a very simple framework of physics beyond the Standard Model (SM) to supplement the SM with a DM candidate. In this paper, we consider an ultraviolet completion of the scenario to an SO(10) grand unified theory, which is a well-motivated framework in light of the neutrino oscillation data. Considering various phenomenological constraints, such as the successful SM gauge coupling unification, the proton stability, and the direct/indirect DM detection constraints as well as the absolute electroweak vacuum stability, we have first singled out the minimal particle content of the MDM scenario at low energies. In addition to the SM particle content, our MDM scenario includes an SU(2)$_L$ quintet scalar DM with a 9.4 TeV mass and three degenerate color-octet scalars with mass of 2 TeV. We then have found a way to embed the minimal particle content into SO(10) representations, in which a remnant $Z_2$ symmetry after the SO(10) symmetry breaking ensures the stability of the DM particle. The production cross section of the color-octet scalars at the Large Hadron Collider is found to be a few orders of magnitude below the current experimental bound.

Vacuum stability with radiative Yukawa couplings

We explore the electroweak vacuum stability in the framework of a recently proposed paradigm for the origin of Yukawa couplings. These arise as low energy effective couplings radiatively generated by portal interactions with a hidden, or dark, sector at the one-loop level. Possible tree-level Yukawa couplings are forbidden by a new underlying symmetry, assumed to be spontaneously broken by the vacuum expectation value of a new scalar field above the electroweak scale. As a consequence, the top Yukawa interaction ceases to behave as a local operator at energies above the new sector scale and, therefore, cannot contribute to the running of the quartic Higgs coupling at higher energies. By studying two complementary scenarios, we explicitly show that the framework can achieve the stability of the electroweak vacuum without particular tuning of parameters. The proposed mechanism requires the existence of a dark sector and new portal messenger scalar interactions that, connecting the Standard Model to the dark sector fields, could be tested at the LHC and future collider experiments.

GUT-scale constrained SUSY in light of new muon g-2 measurement

The new FNAL result of the muon g−2, combined with the BNL result, shows a 4.2σ deviation from the SM. We use the new data of the muon g−2 to revisit several GUT-scale constrained SUSY models with the constraints from the LHC searches, the dark matter detection, the flavour data and the electroweak vacuum stability. We first demonstrate the tension between the muon g−2 and other experimental measurements in the CMSSM/mSUGRA. Then after discussing the possible ways to alleviate such a tension and showing the muon g−2 in pMSSM under relevant experimental constraints, we survey several extensions of the CMSSM/mSUGRA with different types of universal boundary conditions at the GUT scale. Finally, we briefly discuss the muon g−2 in other popular SUSY breaking mechanisms, namely the GMSB and AMSB mechanisms and their extensions.

Two component singlet-triplet scalar dark matter and electroweak vacuum stability

We propose a two component dark matter setup by extending the Standard Model with a singlet and a hyperchargeless triplet scalars, each of them being odd under different ${Z}_{2}$ symmetries. We observe that the interconversion between the two dark matter components allow a viable parameter space where masses of both the dark matter candidates can be below TeV, even though their individual contribution to single component dark matter rules out any such sub-TeV dark matter. We find that a lighter mass of the neutral component of the scalar triplet, playing the role of one dark matter component, compared to the singlet one is favored. In addition, the setup is shown to make the electroweak vacuum absolutely stable till the Planck scale, thanks to Higgs portal coupling with the scalar dark matter components.

Scrutinizing vacuum stability in IDM with Type-III inverse seesaw

We consider the extension of the Standard Model (SM) with an inert Higgs doublet that also contains two or three sets of SU(2)L triplet fermions with hypercharge zero and analyze the stability of electroweak vacuum for the scenarios. The model represents a Type-III inverse seesaw mechanism for neutrino mass generation with a Dark matter candidate. An effective potential approach calculation with two-loop beta function have been carried out in deciding the fate of the electroweak vacuum. Weak gauge coupling g2 shows a different behaviour as compared to the Standard Model. The modified running of g2, along with the Higgs quartic coupling and Type-III Yukawa couplings become crucial in determining the stability of electroweak vacuum. The interplay between two and three generations of such triplet fermions reveals that extensions with two generations is favoured if we aspire for Planck scale stability. Bounds on the Higgs quartic couplings, Type-III Yukawa and number of triplet fermion generations are drawn for different mass scale of Type-III fermions. The phenomenologies of inert doublet and Type-III fermions at the LHC and other experiments are commented upon.

Sub-TeV singlet scalar dark matter and electroweak vacuum stability with vectorlike fermions

We study a scalar singlet dark matter (DM) having mass in sub-TeV regime by extending the minimal scalar singlet DM setup by additional vector like fermions. While the minimal scalar singlet DM satisfies the relic and direct detection constraints for mass beyond TeV only, presence of its portal coupling with vector like fermions opens up additional co-annihilation channels. These vector like fermions also help in achieving electroweak vacuum stability all the way up to Planck scale. We find that for one generation of vector like quarks consisting of a $SU(2)_L$ doublet and a singlet, scalar singlet DM with mass a few hundred GeV can indeed satisfy relic, direct detection and other relevant constraints while also making the electroweak vacuum absolutely stable. The same can be achieved by introducing vector like leptons too, but with three generations. While the model with vector like quarks is minimal, the three generations of vector like lepton doublet and neutral singlet can also give rise to light neutrino mass at one loop level.

The upper bounds on supersymmetry breaking scales in split supersymmetry from the Higgs mass and electroweak vacuum stability

Abstract The null results of the LHC searches have put strong bounds on new physics scenarios such as supersymmetry (SUSY). With the latest values for the top quark mass and strong coupling, we study the upper bounds on the sfermion masses in split SUSY from the observed Higgs boson mass and electroweak (EW) vacuum stability. To be consistent with the observed Higgs mass, we find that the largest values of supersymmetry breaking scales $M_{S}$ for $\tan\beta=2$, $\tan\beta=4$, and $\tan\beta=50$ are $10^{6.2}$, $10^{4.5}$, and $10^{4.3}\, {\rm GeV}$, respectively. In particular, split SUSY with $\tan\beta \gtrsim 4$ can be probed in future 100 TeV proton–proton colliders such as FCC-hh and SppC. In addition, the Higgs quartic coupling becomes negative at about $10^{8.2}$, $10^{8.7}$, and $10^{9.6}\, {\rm GeV}$ respectively for $m_h =$ 123, 125, and 127 GeV from EW vacuum stability. These bounds are about one order smaller than the Standard Model due to the extra Higgs–Higgsino–gaugino couplings. We briefly comment on the lifetime of gluinos in our study and compare it with the current LHC observations. Additionally, we comment on the prospects of the discovery of prompt gluinos at the FCC-hh and SppC.

Electroweak vacuum stability and the Higgs field relaxation via gravitational effects

The measured values of the standard model parameters favors a shallow metastable electroweak vacuum and a deep global minimum. The Higgs relaxation in its present local minimum can only be explained via a large degree of fine-tuning. In this paper, irrespective of new physics beyond the SM, we study the universal effect of gravity on the Higgs dynamics in the early universe. We consider a two-parameter framework in which the Higgs is non-minimally coupled to a higher-curvature gravity. In the Einstein frame there are genuine couplings between the Higgs field and the Weyl field with interesting predictions. In a broad region in the parameter space and for large field values, the effective Higgs mass is large and thus it initially takes over the dynamics by its coherent oscillations. Finally, the Weyl (inflaton) field with its plateau-like potential dominates and derives cosmic inflation. In this framework, the Higgs self-coupling in the electroweak vacuum is modified by contributions from gravity sector.

Constraining the minimal type-III seesaw model with naturalness, lepton flavor violation, and electroweak vacuum stability

We study the minimal type-III seesaw model in which we extend the SM by adding two $SU(2)_L$ triplet fermions with zero hypercharge to explain the origin of the non-zero neutrino masses. We show that the naturalness conditions and the limits from lepton flavor violating decays provide very stringent bounds on the model parameters along with the constraints from the stability/metastability of the electroweak vacuum. We perform a detailed analysis of the model parameter space including all the constraints for both normal as well as inverted hierarchies of the light neutrino masses. We find that most of the region that are allowed by lepton flavor violating decays and naturalness fall in the stable/metastable region depending on the values of the standard model parameters.

Pseudo-Dirac Higgsino dark matter in GUT scale supersymmetry

We investigate a scenario in which supersymmetry is broken at a scale MS ≥ 1014 GeV leaving only a pair of Higgs doublets, their superpartners (Higgsinos) and a gauge singlet fermion (singlino) besides the standard model fermions and gauge bosons at low energy. The Higgsino-singlino mixing induces a small splitting between the masses of the electrically neutral components of Higgsinos which otherwise remain almost degenerate in GUT scale supersymmetry. The lightest combination of them provides a viable thermal dark matter if the Higgsino mass scale is close to 1 TeV. The small mass splitting induced by the singlino turns the neutral components of Higgsinos into pseudo-Dirac fermions which successfully evade the constraints from the direct detection experiments if the singlino mass is ≲ 108 GeV. We analyse the constraints on the effective framework, arising from the stability of electroweak vacuum, observed mass and couplings of the Higgs, and the limits on the masses of the other scalars, by matching it with the next-to-minimal supersymmetric standard model at MS. It is found that the presence of singlino at an intermediate scale significantly improves the stability of electroweak vacuum and allows a stable or metastable vacuum for almost all the values of tan β while the observed Higgs mass together with the limit on the charged Higgs mass favours tan β ≲ 3.

Phenomenology of the inflation-inspired NMSSM at the electroweak scale

The concept of Higgs inflation can be elegantly incorporated in the Next-to-Minimal Supersymmetric Standard Model (NMSSM). A linear combination of the two Higgs-doublet fields plays the role of the inflaton which is non-minimally coupled to gravity. This non-minimal coupling appears in the low-energy effective superpotential and changes the phenomenology at the electroweak scale. While the field content of the inflation-inspired model is the same as in the NMSSM, there is another contribution to the mu term in addition to the vacuum expectation value of the singlet. We explore this extended parameter space and point out scenarios with phenomenological differences compared to the pure NMSSM. A special focus is set on the electroweak vacuum stability and the parameter dependence of the Higgs and neutralino sectors. We highlight regions which yield a SM-like 125,hbox {GeV} Higgs boson compatible with the experimental observations and are in accordance with the limits from searches for additional Higgs bosons. Finally, we study the impact of the non-minimal coupling to gravity on the Higgs mixing and in turn on the decays of the Higgs bosons in this model.

Loop induced H±→W±Z decays in the aligned two-Higgs-doublet model

We present a complete one-loop computation of the $H^\pm \rightarrow W^\pm Z$ decay in the aligned two-Higgs-doublet model. The constraints from the electroweak precision observables, perturbative unitarity, vacuum stability and flavour physics are all taken into account along with the latest Large Hadron Collider searches for the charged Higgs. It is observed that a large enhancement of the branching ratio can be obtained in the limit where there is a large splitting between the charged and pseudo-scalar Higgs masses as well as for the largest allowed values of the alignment parameter $\varsigma_u$. We find that the maximum possible branching ratio in the case of a large mass splitting between $m_{H^\pm}$ and $m_A$ is $\approx 10^{-3}$ for $m_{H^\pm} \in (200,700)$ GeV which is in the reach of the high luminosity phase of the Large Hadron Collider.

Scalar assisted singlet doublet fermion dark matter model and electroweak vacuum stability

We extend the so-called singlet doublet dark matter model, where the dark matter is an admixture of a Standard Model singlet and a pair of electroweak doublet fermions, by a singlet scalar field. The new portal coupling of it with the dark sector not only contributes to the dark matter phenomenology (involving relic density and direct detection limits), but also becomes important for generation of dark matter mass through its vacuum expectation value. While the presence of dark sector fermions affects the stability of the electroweak vacuum adversely, we find this additional singlet is capable of making the electroweak vacuum absolutely stable upto the Planck scale. A combined study of dark matter phenomenology and Higgs vacuum stability issue reflects that the scalar sector mixing angle can be significantly constrained in this scenario.