Higgs Model Research Articles

Remarks on the Clauser-Horne-Shimony-Holt inequality in relativistic quantum field theory

We present an investigation of the Clauser-Horne-Shimony-Holt (CHSH) inequality within a relativistic quantum field theory model built up with a pair of free massive scalar fields $({\ensuremath{\varphi}}_{A},{\ensuremath{\varphi}}_{B})$ where, as is customary, the indices $(A,B)$ refer to Alice and Bob, respectively. A set of bounded Hermitian operators is introduced by making use of the Weyl operators. A CHSH-type correlator is constructed and evaluated in the Fock vacuum by means of canonical quantization. Although the observed violation of the CHSH inequality turns out to be rather small as compared to Tsirelson's bound of quantum mechanics, the model can be employed for the study of Bell's inequalities in the more physical case of gauge theories such as the Higgs models, for which local Becchi-Rouet-Stora-Tyutin (BRST) invariant operators describing both the massive gauge boson as well as the Higgs particle have been devised. These operators can be naturally exponentiated, leading to BRST invariant type of Weyl operators useful to analyze Bell's inequalities within an invariant BRST environment.

Issues in Palatini R2 inflation: Bounds on the reheating temperature

We consider ${\mathcal{R}}^{2}$ inflation in Palatini gravity, in the presence of scalar fields coupled to gravity. These theories, in the Einstein frame, and for one scalar field $h$, share common features with $K$-inflation models. We apply this formalism for the study of single-field inflationary models, whose potentials are monomials, $V\ensuremath{\sim}{h}^{n}$, with $n$ a positive even integer. We also study the Higgs model nonminimally coupled to gravity. With ${\mathcal{R}}^{2}$ terms coupled to gravity as $\ensuremath{\sim}\ensuremath{\alpha}{\mathcal{R}}^{2}$, with $\ensuremath{\alpha}$ constant, the instantaneous reheating temperature ${T}_{ins}$, is bounded by ${T}_{ins}\ensuremath{\le}0.290{m}_{\text{Planck}}/{\ensuremath{\alpha}}^{1/4}$, with the upper bound being saturated for large $\ensuremath{\alpha}$. For such large $\ensuremath{\alpha}$ need go beyond slow roll to calculate reliably the cosmological parameters, among these the end of inflation through which ${T}_{ins}$ is determined. In fact, as the inflaton rolls towards the end of the inflation point, the quartic in the velocity terms, unavoidable in Palatini gravity, play a significant role and cannot be ignored. The values of $\ensuremath{\alpha}$, and other parameters, are constrained by cosmological data, setting bounds on the inflationary scale ${M}_{s}\ensuremath{\sim}1/\sqrt{\ensuremath{\alpha}}$ and the reheating temperature of the Universe.

Dilaton Effective Field Theory

We review and extend recent studies of dilaton effective field theory (dEFT) that provide a framework for the description of the Higgs boson as a composite structure. We first describe the dEFT as applied to lattice data for a class of gauge theories with near-conformal infrared behavior. This includes the dilaton associated with the spontaneous breaking of (approximate) scale invariance and a set of pseudo-Nambu–Goldstone bosons (pNGBs) associated with the spontaneous breaking of an (approximate) internal global symmetry. The theory contains two small symmetry-breaking parameters. We display the leading-order (LO) Lagrangian and review its fit to lattice data for the SU(3) gauge theory with Nf=8 Dirac fermions in the fundamental representation. We then develop power-counting rules to identify the corrections emerging at next-to-leading order (NLO) in the dEFT action. We list the NLO operators that appear and provide estimates for the coefficients. We comment on implications for composite Higgs model building.

Partial compositeness under precision scrutiny

We revisit the impact of top partial compositeness on electroweak precision observables in the misaligned vacuum basis. We identify a new source for S in the singlet mixing case, and for S-T in the bi-doublet mixing, stemming from misalignment in the gauge couplings of the top partners. Hence, a positive shift in T can be obtained in both cases, as preferred by the recent CDF measurement of the W mass. These results, obtained for the minimal fundamental coset SU(4)/Sp(4), apply to any composite Higgs model with top partial compositeness.

Exploring extended Higgs sectors via pair production at the LHC

Higgs sectors extended by electroweakly charged scalars can be explored by scalar pair production at the LHC. We consider a fermiophobic scenario, with decays into a pair of gauge bosons, and a fermiophilic one, with decays into top and bottom quarks. After establishing the current bounds on simplified models, we focus on an SU(5)/SO(5) composite Higgs model. This first exploration demonstrates the need for dedicated searches at current and future colliders.

The Contribution of Charged Bosons with Right-Handed Neutrinos to the Muon g − 2 Anomaly in the Twin Higgs Models

We examine the charged boson and right-handed neutrino contribution to the muon g−2 anomaly in twin Higgs models with joint constraints of Higgs global fit data, precision electroweak data, leptonic flavor-changing decay μ→eγ, and the mass requirement of heavy-gauge bosons. It comes with the conclusion that some parameters, such as the coupling of charged Higgs to the lepton yμ, the top Yukawa yt, and heavy-gauge boson coupling to the lepton Vμ are constrained roughly in the range of 0.12≲yμ≲0.4, 0.4≲yt≲0.9, and 0.47≲Vμ≲1, respectively.

Research on the electromagnetic and weak dipole moments of the tau-lepton at the Bestest Little Higgs Model

In this paper, using the Bestest Little Higgs Model (BLHM) we calculate at the one-loop level the contributions to the Anomalous Magnetic Dipole Moment (AMDM) and Anomalous Weak Magnetic Dipole Moment (AWMDM) of the tau-lepton. The implications from this model are studied, emphasizing the contributions of the new physics induced by the new scalar and vector bosons of the BLHM: S_i=H_0, A_0, phi ^{0}, eta ^{0}, sigma , H^{pm }, phi ^{pm }, eta ^{pm }, and V_i=Z', W'^{pm } because these quantify the new physics. With these new contributions, we estimated bounds on the real and imaginary parts of the AMDM and AWMDM of the tau-lepton. Our study complements other one-loop-level research performed on models beyond the Standard Model.

What can we learn from the total width of the Higgs boson?* *Supported in part by the National Science Foundation of China (11725520, 11675002, 11635001, 12022514, 11875003, 12047503). JHY is also supported by the National Key Research and Development Program of China (2020YFC2201501)

As one of the key properties of the Higgs boson, the Higgs total width is sensitive to the global profile of the Higgs boson couplings, and thus new physics would modify the Higgs width. We investigate the total width in various new physics models, including various scalar extensions, composite Higgs models, and the fraternal twin Higgs model. Typically, the Higgs width is smaller than the standard model value due to mixture with other scalars if the Higgs is elementary, or curved Higgs field space for the composite Higgs. On the other hand, except for the possible invisible decay mode, the enhanced Yukawa coupling in the two Higgs doublet model or the exotic fermion embeddings in the composite Higgs could enhance the Higgs width greatly. The precision measurement of the Higgs total width at the high-luminosity LHC can be used to discriminate certain new physics models.

Weak dipole moments of the top-quark at the Bestest Little Higgs model

Weak dipole moments of the top-quark at the Bestest Little Higgs model

Testing the charge-radius coupling of composite Goldstone (Higgs) bosons at hadron colliders

We explore the collider relevance of a charge-radius coupling among light mesons in composite Higgs models. In particular, we focus of a coupling of the photon to the composite Higgs and a composite singlet, arising from isospin violation in the underlying theory. This coupling offers a deep probe of the composite nature of the Higgs mechanism, being sensitive to the electromagnetic and weak isospin structure of its constituents. The main collider effect consists in the production of the Higgs boson in association with a light composite pseudo-scalar. We present an exploratory cut-and-count analysis at hadron colliders, like the LHC, showing that an efficient background suppression can be achieved. More sophisticated techniques, however, are necessary to select a sufficient number of signal events, due to the small production rates. This justifies further investigation of this channel, which is highly complementary to other searches for compositeness in the Higgs sector.

Phenomenological implications of the new Littlest Higgs model with T-parity

We investigate the parameter space of the new Littlest Higgs model with T-parity (NLHT) recently introduced to cure some pathologies of the original LHT. The model requires extra fermion content and additional pseudo-Goldstone bosons. While the heavy top quark sector is similar, there are both T-odd and T-even heavy quarks and leptons with masses proportional to just two sets of Yukawa matrices in flavor space, one more than in the LHT. The new scalars are a singlet and real triplet, T-odd, with masses controlled by gauge and Yukawa couplings, independent of the spontaneous symmetry breaking scale f, and hence potentially light. Imposing that no mass exceeds the cutoff scale, applying current lower bounds on vector-like quarks and assuming a simplified model with mass degenerate heavy fermions compatible with the heavy photon as dark matter constituent, we find that f gets constrained within the interval between 2 and 3 TeV, the common Yukawa coupling of heavy leptons gets fixed and the Yukawa coupling of heavy quarks becomes greatly correlated to the top quark Yukawa couplings. The particle spectrum is then bounded from below and above, with the (lightest) heavy photon at about 0.5 TeV, not far from the heavy leptons, the new scalars below 1 TeV, the usual complex scalar triplet close to the heavy weak bosons at about 1.5 to 2.5 TeV, and the heavy quarks and top quark partners between 2 and 5 TeV. The new scalars decay predominantly to a standard and a T-odd lepton and have a width comparable to that of the Higgs.

Soliton stars in Yang-Mills-Higgs theories

Bosonic field theories with self interactions alongside gravity, generally admit bound states known as solitons. Depending upon the spin nature of the field, they can even carry macroscopic intrinsic spin polarization. Focusing on the SU($2$) case, we describe polarized solitons in non-Abelian theories with a heavy Higgs, which we refer to as `Yang-Mills stars'. Owing to both kinds of self-interactions; repulsive ones arising due to the Yang-Mills structure, while attractive ones arising due to the Higgs exchange; we can have a diverse zoo of solitons. Depending upon various parameters of the theory such as the mass of the Yang-Mills vector fields $m$, mass of the dark Higgs field $M_{\varphi}$, and the gauge coupling constant $g$, these objects can be astrophysically large with varying size and mass, and carry large intrinsic spin and/or iso-spin giving rise to interesting phenomenological implications. Even for vector mass as large as $m \simeq 10$ eV, we can accommodate gauge couplings $g \lesssim 10^{-4}-10^{-5}$, still evading Bullet cluster constraints. For these parameters, there may exist cosmologically long lived solitons having radii as large as $r_{s} \sim 10^{5}\,R_{\odot}$ and masses $M_{s} \sim 10 M_{\odot}$, carrying $M_{s}/m \sim 10^{66}$ amounts of intrinsic spin and iso-spin polarization. As a subset of the space of soliton solutions in the SU($2$) Higgs model, in the end we also explicitly discuss solitons in the Abelian Higgs model.

Techni-composite Higgs models with symmetric and asymmetric dark matter candidates

We propose a novel class of composite models that feature both a technicolor and a composite Higgs vacuum limit, resulting in an asymmetric dark matter candidate. These techni-composite Higgs models are based on an extended left-right electroweak symmetry with a pseudo-Nambu Goldstone boson Higgs and stable dark matter candidates charged under a global $\mathrm{U}(1{)}_{X}$ symmetry, connected to the baryon asymmetry at high temperatures via the $\mathrm{SU}(2{)}_{\mathrm{R}}$ sphaleron. We consider, as explicit examples, four-dimensional gauge theories with fermions charged under a new confining gauge group ${G}_{\mathrm{HC}}$.

Charged dark matter in supersymmetric twin Higgs models

Supersymmetric Twin Higgs models ameliorate the fine-tuning of the electroweak scale originating from the heavy scalar top partners required by the non-discovery of them at the Large Hadron Collider. If the Lightest Supersymmetric Particle resides in the twin sector, it may play the role of dark matter even if it is charged under twin gauge interactions. We show that the twin stau is a viable candidate for charged dark matter, even if the twin electromagnetic gauge symmetry is unbroken, with thermal relic abundance that naturally matches the observed dark matter abundance. A wide parameter space satisfies all the experimental constraints including those on dark matter self-interactions. Twin stau dark matter can be observed in future direct detection experiments such as LUX-ZEPLIN. The stau has a mass in the range of 300–500 GeV, and in the minimal scenario, has a decay length long enough to be observed as a disappearing track or a long-lived particle at the Large Hadron Collider.

Form factors in Higgs couplings from physics beyond the standard model

We consider the momentum-dependent effects in Higgs couplings generated by physics beyond the standard model. We take a model-dependent approach, in which we can fully compute the non-local effects from physics not directly reachable by the LHC energy. We consider several scenarios, including composite Higgs models, additional scalars, and the continuum contributions of a quasi-conformal sector, as examples. For each specific model, we are able to obtain the form factor, with which it is then possible to fully simulate the effects in kinematics distributions. The momentum-dependent effects appear as a consequence of off-shellness in the process. We show how the sensitivity of different channels to the various models depends on how the flow of off-shellness appears in the Higgs couplings.

Lepton flavor violation within the simplest little Higgs model

We carry out an exhaustive analysis of lepton flavor violating processes within the Simplest Little Higgs model. Its discovery could be expected from either $\mu\to e$ conversion in nuclei, $\mu\to e\gamma$ or $\mu\to3e$ decays. Then, the tau sector could help discriminating this model not only via $\tau\to\ell\gamma$ ($\ell=\mu,e$) and $\tau\to3\ell$ decays, but also by means of $\ell\to\tau$ conversion in nuclei, which is promising in this respect. Although the model violates slightly custodial symmetry, acommodating the recent CDF $M_W$ measurement is in tension with electroweak precision data.

Lepton flavour violation in hadron decays of the tau lepton within the littlest Higgs model with T-parity

We first study the hadronic lepton flavor violating tau decays within the littlest Higgs model with T-parity (including one or two pseudoscalars, or a vector resonance). We consider the case where only T-odd particles and partner fermions contribute, and also its extension including Majorana neutrinos coming from an inverse seesaw. In both cases our mean values lie mostly only one order of magnitude below current upper limits, strengthening the case of searching for these decays in the quest for new physics.

Environmental selection of the cosmological constant and electroweak scales

We investigate whether selfish/Goldilocks Higgs models can be extended to accomodate vacua with both the right Higgs mass and cosmological constant. Through the introduction of multiple four-form fields coupled with the Higgs scalar boson we find that both the cosmological constant and the electroweak hierarchy problems can be addressed simultaneously, without inserting the relevant physical scales by hand and avoiding fine tuning. The resulting bounds on the brane charges, the only dimensionful free parameter of the theory, depend on the strength of the four-form scalar coupling and can be of the same order of magnitude as those necessary for a solution to the cosmological constant problem alone via the Bousso-Polchinski mechanism.

Tunneling potentials for the tunneling action: gauge invariance

We formulate a procedure to obtain a gauge-invariant tunneling rate at zero temperature using the recently developed tunneling potential approach. This procedure relies on a consistent power counting in gauge coupling and a derivative expansion. The tunneling potential approach, while numerically more efficient than the standard bounce solution method, inherits the gauge-dependence of the latter when naïvely implemented. Using the Abelian Higgs model, we show how to obtain a tunneling rate whose residual gauge-dependence arises solely from the polynomial approximations adopted in the tunneling potential computation.

Generalized Abelian Higgs model with analytical vortex solutions

We study topological vortex solutions in a generalized Abelian Higgs model with nonpolynomial dielectric and potential functions. These quantities are chosen by requiring integrability of the self-dual limit of the theory for all values of the magnetic flux. All the vortex profiles are described by exact analytical expressions that solve the self-dual vortex equations. There is only a symmetry-breaking superconducting phase and the model sustains regular phenomenology.