Vacuum Stability Problem Research Articles

Critical behavior and stability problem in a scalar field model

As shown in the works [1-3], the asymptotic behavior of the propagator in the Euclidean region of momenta for the model of a complex scalar field φ and a real scalar field χ with the interaction drastically changes depending on the value of the coupling constant. For small values of the coupling, the propagator of the field φ behaves asymptotically as free, while in the strong-coupling region the propagator in the deep Euclidean region tends to be a constant. In this paper, the influence of the vacuum stability problem of this model on this critical behavior is investigated. It is shown that within the framework of the approximations used, the addition of a stabilizing term of type to the Lagrangian leads to a renormalization of the mass and does not change the main effect of changing the ultraviolet behavior of the propagator. PACS number: 11.10.Jj.

Natural Higgs inflation, gauge coupling unification, and neutrino masses

We present a class of nonsupersymmetric models in which the so-called critical Higgs inflation [Formula: see text] can be naturally realized without using specific values for Higgs and top quark masses. In these scenarios, the Standard Model (SM) vacuum stability problem, gauge coupling unification, neutrino mass generation and Higgs inflation mechanism are linked to each other. We adopt in our models Type I seesaw mechanism for neutrino masses. An appropriate choice of the Type I seesaw scale allows us to have an arbitrarily small but positive value of SM Higgs quartic coupling around the inflation scale. We present a few benchmark points where we show that the scalar spectral indices are around 0.9626 and 0.9685 for the number of [Formula: see text]-folding [Formula: see text] and [Formula: see text], respectively. The tensor-to-scalar ratios are of the order of [Formula: see text]. The running of the scalar spectral index is negative and is of the order of [Formula: see text].

Phase transition and vacuum stability in the classically conformal B\u2013L model

Within classically conformal models, the spontaneous breaking of scale invariance is usually associated to a strong first order phase transition that results in a gravitational wave background within the reach of future space-based interferometers. In this paper we study the case of the classically conformal gauged B–L model, analysing the impact of this minimal extension of the Standard Model on the dynamics of the electroweak symmetry breaking and derive its gravitational wave signature. Particular attention is paid to the problem of vacuum stability and to the role of the QCD phase transition, which we prove responsible for concluding the symmetry breaking transition in part of the considered parameter space. Finally, we calculate the gravitational wave signal emitted in the process, finding that a large part of the parameter space of the model can be probed by LISA.

The minimal GUT with inflaton and dark matter unification

Giving up the solutions to the fine-tuning problems, we propose the non-supersymmetric flipped SU(5)times U(1)_X model based on the minimal particle content principle, which can be constructed from the four-dimensional SO(10) models, five-dimensional orbifold SO(10) models, and local F-theory SO(10) models. To achieve gauge coupling unification, we introduce one pair of vector-like fermions, which form a complete SU(5)times U(1)_X representation. The proton lifetime is around 5times 10^{35} years, neutrino masses and mixing can be explained via the seesaw mechanism, baryon asymmetry can be generated via leptogenesis, and the vacuum stability problem can be solved as well. In particular, we propose that inflaton and dark matter particles can be unified to a real scalar field with Z_2 symmetry, which is not an axion and does not have the non-minimal coupling to gravity. Such a kind of scenarios can be applied to the generic scalar dark matter models. Also, we find that the vector-like particle corrections to the B_s^0 masses might be about 6.6%, while their corrections to the K^0 and B_d^0 masses are negligible.

High-scale validity of a two-Higgs-doublet scenario: Predicting collider signals

It is possible to ameliorate the Higgs vacuum stability problem by switching over to two Higgs doublet models (2HDM), ensuring a stable electroweak vacuum up to the Planck scale, even though the top quark mass may be on the high side. However, the simultaneous requirements of perturbative unitarity, and also compatibility with collider and flavour data, constrain the parameter space severely. We investigate the collider signals answering to the regions allowed by such constraints. In particular, the near degeneracy of the neutral heavy scalar and the pseudoscalar is a feature that is probed. The LHC allows distinguishability of these two states, together with signal significance of at least 3$\sigma$, in its high-luminosity run. While $e^+ e^-$ colliders may have rather low event rates, muon colliders, cashing on the principle of radiative return, can probe 2HDM scenarios with (pseudo)scalar masses up to a TeV or so, though with the price of losing distinction between the CP-even and odd states.

Natural relaxation

Motivated by natural inflation, we propose a relaxation mechanism consistent with inflationary cosmology that explains the hierarchy between the electroweak scale and Planck scale. This scenario is based on a selection mechanism that identifies the low-scale dynamics as the one that is screened from UV physics. The scenario also predicts the near-criticality and metastability of the Standard Model (SM) vacuum state, explaining the Higgs boson mass observed at the Large Hadron Collider (LHC). Once Majorana right-handed neutrinos are introduced to provide a viable reheating channel, our framework yields a corresponding mass scale that allows for the seesaw mechanism as well as for standard thermal leptogenesis. We argue that considering singlet scalar dark matter extensions of the proposed scenario could solve the vacuum stability problem and discuss how the cosmological constant problem is possibly addressed.

Electroweak vacuum stability and diphoton excess at 750 GeV**Supported by Innovation Program of the Institute of High Energy Physics (Y4515570U1), National Youth Thousand Talents Program, and CAS Center for Excellence in Particle Physics (CCEPP)

Recently, both ATLAS and CMS collaborations at the CERN Large Hadron Collider (LHC) announced their observations of an excess of diphoton events around the invariant mass of 750 GeV with a local significance of 3.6σ and 2.6σ, respectively. In this paper, we interpret the diphoton excess as the on-shell production of a real singlet scalar in the pp → S → γγ channel. To accommodate the observed production rate, we further introduce a vector-like fermion F, which carries both color and electric charges. The viable regions of model parameters are explored for this simple extension of the Standard Model (SM). Moreover, we revisit the problem of electroweak vacuum stability in the same scenario, and find that the requirement for the electroweak vacuum stability up to high energy scales imposes serious constraints on the Yukawa coupling of the vector-like fermion and the quartic couplings of the SM Higgs boson and the new singlet scalar. Consequently, a successful explanation for the diphoton excess and the absolute stability of electroweak vacuum cannot be achieved simultaneously in this economical setup.

Leading QCD-induced four-loop contributions to the β-function of the Higgs self-coupling in the SM and vacuum stability

We present analytical results for the leading top-Yukawa and QCD contribution to the $\beta$-function for the Higgs self-coupling $\lambda$ of the Standard Model at four-loop level, namely the part $\propto y_t^4 g_s^6$ independently confirming a result given in [1]. We also give the contribution $\propto y_t^2 g_s^6$ of the anomalous dimension of the Higgs field as well as the terms $\propto y_t g_s^8$ to the top-Yukawa $\beta$-function which can also be derived from the anomalous dimension of the top quark mass. We compare the results with the RG functions of the correlators of two and four scalar currents in pure QCD and find a new relation between the anomalous dimension $\gamma_0$ of the QCD vacuum energy and the anomalous dimension $\gamma_m^{SS}$ appearing in the RG equation of the correlator of two scalar currents. Together with the recently computed top-Yukawa and QCD contributions to $\beta_{g_s}$ [2,3] the $\beta$-functions presented here constitute the leading four-loop contributions to the evolution of the Higgs self-coupling. A numerical estimate of these terms at the scale of the top-quark mass is presented as well as an analysis of the impact on the evolution of $\lambda$ up to the Planck scale and the vacuum stability problem.

Interpretation of the diphoton excess at CMS and ATLAS

We consider the diphoton resonance at the 13 TeV LHC in a consistent model with new scalars and vector-like fermions added to the Standard Model (SM), which can be constructed from orbifold grand unified theories and string models. The gauge coupling unification can be achieved, neutrino masses can be generated radiatively, and electroweak vacuum stability problem can be solved. To explain the diphoton resonance, we study a spin-0 particle, and discuss various associated final states.

Свойства вакуума и спектр бран струнной теории Tипа IIB

F-theory has been receiving more attention in the past few years because its rich structure allows to solve many problems of the Standard Model and Grand Unification Theory. This theory is also important because of the necessity to solve the problem of vacuum stability. A simpler solution of F-theory is used to describe the Type IIB string theory. For the classification of D-brane charges in superstring theory of Type IIB is applied K-theory. This approach provides an access to gauge fields connected with vector bundles, classified by K-theory. This technique implements the resolution of issues related to the structure of scales and hierarchies, the gauge group and charged matter content.

Vacuum Stability and Two Loop Threshold Corrections to the Higgs Quartic Coupling

We review the vacuum stability problem in the Standard Model by studying the next-to-next-to-leading order (NNLO) shape of the renormalization group improved effective potential by including the threshold corrections of the SM couplings. For this purpose we computed the sum of the vacuum bubbles diagrams up two-loop level and the Higgs tadpoles contributions by two different methods in an on-shell renormalization scheme where the renormalized parameters are directly expressed in terms of physical observables.

Supersymmetry after the Higgs

A brief review is given of the implications of a 126 GeV Higgs boson for the discovery of supersymmetry. Thus a 126 GeV Higgs boson is problematic within the Standard Model because of vacuum instability pointing to new physics beyond the Standard Model. The problem of vacuum stability is overcome in the SUGRA GUT model but the 126 GeV Higgs mass implies that the average SUSY scale lies in the several TeV region. The largeness of the SUSY scale relieves the tension on SUGRA models since it helps suppress flavor changing neutral currents and CP violating effects and also helps in extending the proton life time arising from baryon and lepton number violating dimension five operators. The geometry of radiative breaking of the electroweak symmetry and fine tuning in view of the large SUSY scale are analyzed.Consistency with the Brookhaven result is discussed. It is also shown that a large SUSY scale implied by the 126 GeV Higgs boson mass allows for light gauginos (gluino, charginos, neutralinos) and sleptons. These along with the lighter third generation squarks are the prime candidates for discovery at RUN II of the LHC. Implication of the 126 GeV Higgs boson for the direct search for dark matter is discussed. Also discussed are the sparticles mass hierarchies and their relationship with the simplified models under the Higgs boson mass constraint.

Two component dark matter with multi-Higgs portals

With the assistance of two extra groups, i.e., an extra hidden gauge group $SU(2)_D$ and a global $U(1)$ group, we propose a two component dark matter (DM) model. After the symmetry $SU(2)_D\times U(1)$ being broken, we obtain both the vector and scalar DM candidates. The two DM candidates communicate with the standard model (SM) via three Higgs as multi-Higgs portals. The three Higgs are mixing states of the SM Higgs, the Higgs of the hidden sector and real part of a supplement complex scalar singlet. We study relic density and direct detection of DM in three scenarios. The resonance behaviors and interplay between the two component DM candidates are represented through investigating of the relic density in the parameter spaces of the two DMs masses. The electroweak precision parameters constrains the two Higgs portals couplings ($\lambda_m$ and $\delta_2$). The relevant vacuum stability and naturalness problem in the parameter space of $\lambda_m$ and $\delta_2$ are studied as well. The model could alleviate these two problems in some parameter spaces under the constraints of electroweak precision observables and Higgs indirect search.

Two component Higgs-portal dark matter

In this paper, we construct two component dark matter model and revisit fine-tuning, unitarity and vacuum stability problem in this framework. Through Higgs-portal interactions, the additional scalar and vector singlet fields can interact with the SM particles. The parameter space of the model are severely constraint by observed relic density and direct detection experiments. We found that, unlike the SM, the fine-tuning problem is relaxed due to the modified Veltman condition. The vacuum stability problem is addressed, the additional contributions from two DM singlets to the β function make the Higgs quartic coupling λ(μ) be positive up to Planck scale in some parameter space.

Higgs vacuum stability in theB−Lextended standard model

We study vacuum stability of B-L extension of the Standard Model (SM) and its supersymmetric version. We show that the generation of non-vanishing neutrino masses through TeV inverse seesaw mechanism leads to a cutoff scale of SM Higgs potential stability of order 10^5 GeV. However, in the non-supersymmetric B-L model, we find that the mixing between the SM-like Higgs and the B-L Higgs plays a crucial role in alleviating the vacuum stability problem. We also provide the constraints of stabilizing the Higgs potential in the supersymmetric B-L model.

Vacuum stability and Higgs diphoton decay rate in the Zee-Babu model

Although recent Higgs data from ATLAS and CMS are compatible with a Standard Model (SM) signal at $2\sigma$ level, both experiments see indications for an excess in the diphoton decay channel, which points to new physics beyond the SM. Given such a low Higgs mass $m_H \sim 125 {\rm GeV}$, another sign indicating the existence of new physics beyond the SM is the vacuum stability problem, i.e., the SM Higgs quartic coupling may run to negative values at a scale below the Planck scale. In this paper, we study the vacuum stability and enhanced Higgs diphoton decay rate in the Zee-Babu model, which was used to generate tiny Majorana neutrino masses at two-loop level. We find that it is rather difficult to find overlapping regions allowed by the vacuum stability and diphoton enhancement constraints. As a consequence, it is almost inevitable to introduce new ingredients into the model, in order to resolve these two issues simultaneously.

Higgs vacuum stability, neutrino mass, and dark matter

Recent results from ATLAS and CMS point to a narrow range for the Higgs mass: ${M}_{H}\ensuremath{\in}(124,126)\text{ }\text{ }\mathrm{GeV}$. Given this range, a case may be made for new physics beyond the Standard Model (SM) because of the resultant vacuum stability problem, i.e., the SM Higgs quartic coupling may run to negative values at a scale below the Planck scale. We study representative minimal extensions of the SM that can keep the SM Higgs vacuum stable to the Planck scale by introducing new scalar or fermion interactions at the TeV scale while solving other phenomenological problems. In particular, we consider the type-II seesaw model, which is introduced to explain the nonzero Majorana masses of the active neutrinos. Similarly, we observe that if the stability of the SM Higgs vacuum is ensured by the running of the gauge sector couplings, then one may require a series of new electroweak multiplets, the neutral component of which can be a cold dark matter candidate. Stability may also point to a new $U(1)$ gauge symmetry, in which the SM Higgs carries a nonzero charge.

Cascade supersymmetry breaking and low-scale gauge mediation

We propose a new class of models with gauge mediated supersymmetry breaking, the cascade supersymmetry breaking. This class of models is consistent with the gravitino mass as low as O(1)eV without having suppressed gaugino masses, nor the Landau pole problems of the gauge coupling constants of the Standard Model below the scale of the grand unification. In particular, there is no supersymmetric vacuum in the vicinity of the supersymmetry breaking vacuum even for such a low gravitino mass. Thus, the model does not have a vacuum stability problem decaying into supersymmetric vacua.

A simplified model for orbifold compactification

The problem of vacuum stability in orbifold compactification is addressed. The spectrum of fermions and the effective potential in a simple model of compactification on the T2/Z2 orbifold with a topologically nontrivial gauge field background is calculated.

Vacuum stability and symmetry breaking in non-Minkowskian space-times

The problem of vacuum stability for interacting scalar fields is studied at the one-loop level in situations where the effective potential may not be used. The method described here involves a calculation of the one-loop effective action using the background-field method. Specific examples discussed are interacting twisted and untwisted scalar fields in S/sup 1/ x R/sup 3/, and self-interacting scalar fields in the static Einstein universe and in flat space-time with topology R/sup 1/ x S/sup 1/ x S/sup 1/ x S/sup 1/. It is shown that in some cases radiative corrections can lead to a phase transition where the classical vacuum state becomes unstable.