Strong Yukawa Research Articles

Successful Freeze-Out of Strongly Interacting Dark Matter with Even-Numbered Interactions.

Strongly interacting massive particles π have been advocated as prominent dark matter candidates when they regulate their relic abundance through odd-numbered 3π→2π annihilation. We show that successful freeze-out may also be achieved through even-numbered interactions XX→ππ once bound states X among the particles of the low-energy spectrum exist. In addition, X-formation hosts the potential of also catalyzing odd-numbered 3π→2π annihilation processes, turning them into effective two-body processes πX→ππ. Bound states are often a natural consequence of strongly interacting theories. We calculate the dark matter freeze-out and comment on the cosmic viability and possible extensions. Candidate theories can encompass confining sectors without a mass gap, glueball dark matter, or ϕ^{3} and ϕ^{4} theories with strong Yukawa or self-interactions.

Renormalisation group running effects in pp→tt¯h\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$pp\\rightarrow t{\\bar{t}}h$$\\end{document} in the Standard Model Effective Field Theory

We study the effects of renormalisation group running of the Wilson coefficients in Standard Model Effective Field Theory, using the process pp→tt¯h\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$pp \\rightarrow t {\\bar{t}}h$$\\end{document} as a showcase. We consider both strong and top Yukawa running effects, since the latter can be relevant in presence of large Wilson coefficients. We study the difference between the use of a dynamical and fixed renormalisation scale by exploring different scenarios for the higher-dimensional operators at the high energy scale of new physics, assumed to be at the TeV scale.

Correlated signals of first-order phase transitions and primordial black hole evaporation

Fermi balls produced in a cosmological first-order phase transition may collapse to primordial black holes (PBHs) if the fermion dark matter particles that comprise them interact via a sufficiently strong Yukawa force. We show that phase transitions described by a quartic thermal effective potential with vacuum energy, 0.1 ≲ B1/4/MeV ≲ 103, generate PBHs of mass, 10−20 ≲ MPBH/M⊙ ≲ 10−16, and gravitational waves from the phase transition (at THEIA/μAres) can be correlated with an isotropic extragalactic X-ray/γ-ray background from PBH evaporation (at AMEGO-X/e-ASTROGAM).

Connecting Electroweak Symmetry Breaking and Flavor: A Light Dilaton D and a Sequential Heavy Quark Doublet Q

The 125 GeV boson is quite consistent with the Higgs boson of the Standard Model (SM), but there is a challenge from Anderson as to whether this particle is in the Lagrangian. As Large Hadron Collider (LHC) Run 2 enters its final year of running, we ought to reflect and make sure we have gotten everything right. The ATLAS and CMS combined Run 1 analysis claimed a measurement of 5.4σ vector boson fusion (VBF) production which is consistent with SM, which seemingly refutes Anderson. However, to verify the source of electroweak symmetry breaking (EWSB), we caution that VBF measurement is too important for us to be imprudent in any way, and gluon–gluon fusion (ggF) with similar tag jets must be simultaneous measured, which should be achievable in LHC Run 2. The point is to truly test the dilaton possibility—the pseudo-Goldstone boson of scale invariance violation. We illustrate EWSB by dynamical mass generation of a sequential quark doublet (Q) via its ultrastrong Yukawa coupling and argue how this might be consistent with a 125 GeV dilaton, D. The ultraheavy 2mQ≳4–5 TeV scale explains the absence of New Physics so far, while the mass generation mechanism shields us from the UV theory for the strong Yukawa coupling. Collider and flavor physics implications are briefly touched upon. Current Run 2 analyses show correlations between the ggF and VBF measurements, but the newly observed tt¯H production at LHC poses a challenge.

Threshold enhancement of diphoton resonances

The data collected by the LHC collaborations at an energy of 13 TeV indicates the presence of an excess in the diphoton spectrum that would correspond to a resonance of a 750 GeV mass. The apparently large production cross section is nevertheless very difficult to explain in minimal models. We consider the possibility that the resonance is a pseudoscalar boson $A$ with a two--photon decay mediated by a charged and uncolored fermion having a mass at the $\frac12 M_A$ threshold and a very small decay width, $\ll 1$ MeV; one can then generate a large enhancement of the $A\gamma\gamma$ amplitude which explains the excess without invoking a large multiplicity of particles propagating in the loop, large electric charges and/or very strong Yukawa couplings. The implications of such a threshold enhancement are discussed in two explicit scenarios: i) the Minimal Supersymmetric Standard Model in which the $A$ state is produced via the top quark mediated gluon fusion process and decays into photons predominantly through loops of charginos with masses close to $\frac12 M_A$ and ii) a two Higgs doublet model in which $A$ is again produced by gluon fusion but decays into photons through loops of vector--like charged heavy leptons. We also comment on a minimal scenario in which the $A$ state couples only to photons through a heavy lepton loop and is both produced and decays through this coupling. In all these scenarios, while the mass of the charged fermion has to be adjusted to be extremely close to half of the $A$ resonance mass, the small total widths are naturally obtained if only suppressed three-body decay channels occur. Finally, the implications of some of these scenarios for dark matter are discussed.

Can the diphoton enhancement at 750 GeV be due to a neutral technipion?

We discuss a scenario in which the diphoton enhancement at $M_{\gamma \gamma}$ = 750 GeV, observed by the ATLAS and CMS Collaborations, is a neutral technipion $\tilde{\pi}^0$. We consider two distinct minimal models for the dynamical electroweak symmetry breaking. In a first one, two-flavor vector-like technicolor (VTC) model, we assume that the two-photon fusion is a dominant production mechanism. We include $\gamma \gamma \to {\tilde \pi}^0$ and production of technipion associated with one or two jets. All the considered mechanisms give similar contributions. With the strong Yukawa (technipion-techniquark) coupling $g_{TC}$ = 10 - 20 we obtain the measured cross section of the "signal". With such values of $g_{TC}$ we get a relatively small $\Gamma_{\rm tot}$. In a second approach, one-family walking technicolor (WTC) model, the isoscalar technipion is produced dominantly via the gluon-gluon fusion. We also discuss the size of the signal at lower energies (LHC, Tevatron) for $\gamma \gamma$ (VTC) and jet-jet (WTC) final states and check consistency with the existing experimental data. We predict a measurable cross section for ${\tilde \pi}^0$ production associated with one or two soft jets. The technipion signal in both models is compared with the SM background diphoton contributions. We observe the dominance of inelastic-inelastic processes for $\gamma \gamma$ induced processes. In the VTC scenario, we predict the signal cross section for purely exclusive $p p \to p p \gamma \gamma$ processes at $\sqrt{s}$ = 13 TeV to be about 0.2 fb. Such a cross section would be, however, difficult to measure with the planned integrated luminosity. In all considered cases the signal is below the background or/and below the threshold set by statistics.

Scattering light by light at 750 GeV at the LHC

We consider the possibility that the diphoton excess at 750 GeV is caused by a new scalar resonance produced in photon fusion. This scenario is parametrised by only one relevant effective couplings and is thus minimal. We show that this setup can reproduce both the production rate and width of the resonance, and is not in conflict with the 8 TeV limits on the diphoton cross section. The scenario also predicts event rates for $WW$, $ZZ$, $Z\gamma$ final states. We suggest to perform precision measurements by studying light-by-light scattering with intact protons detected in forward detectors. We construct a simple model that shows that the required couplings can be achieved with new vectorlike, uncolored fermions (with a strong Yukawa coupling to the resonance) which may also account for the required width.

Links between flavor and electroweak symmetry breaking

Fermion mass generation in the standard model was invented by Weinberg, while it is an old notion that strong Yukawa coupling could be the agent of electroweak symmetry breaking. Observation of the 126 GeV boson has crashed the prospects for such a heavy chiral quark doublet Q. However, the dilaton possibility can only be ruled out by confirming vector boson fusion with Run 2 data at the LHC, which starts only in 2015. We recast the [Formula: see text] condensation scenario as Fermi–Yang model v2.0. A Gap Equation has been constructed, with numerical solution demonstrating dynamical mQ generation; scale invariance of this equation may be consistent with a dilaton. Other consequences to be checked are [Formula: see text] "annihilation stars," and enhanced Bd →μ+μ-, KL →π0νν, and possibly sin ϕs. If verified in Nature, the Agent of BEH mechanism would differ from current perception, the 126 GeV boson would be the first New Physics at the LHC, and we would have enough CP violation for baryogenesis.

Three-loop Standard Model effective potential at leading order in strong and top Yukawa couplings

I find the three-loop contribution to the effective potential for the Standard Model Higgs field, in the approximation that the strong and top Yukawa couplings are large compared to all other couplings, using dimensional regularization with modified minimal subtraction. Checks follow from gauge invariance and renormalization group invariance. I also briefly comment on the special problems posed by Goldstone boson contributions to the effective potential, and on the numerical impact of the result on the relations between the Higgs vacuum expectation value, mass, and self-interaction coupling.

Bootstrap dynamical symmetry breaking with strong Yukawa coupling

The newly discovered 126 GeV boson appears, by all counts, to be the Higgs boson of the Standard Model. Although this seems to exclude the existence of a heavy fourth generation quark doublet Q, for theoretical interest, we document a mechanism of dynamical mass generation via strong Yukawa coupling. The Goldstone boson G (the longitudinal component of the weak boson) couples to Q with Yukawa coupling λ Q . A “bootstrap” gap equation is constructed, where strong λ Q generates large quark mass m Q , thereby breaks electroweak symmetry breaking while self-consistently justifying G as a massless Goldstone particle in the loop. We solve the gap equation numerically and find m Q to be a couple of TeV. Putting in the light Higgs boson raises the strength of λ Q considerably, hence m Q as well, and does not look viable. But the equation allows for a dilaton of scale invariance violation, which has weaker coupling than the Higgs boson, except for gg and γγ modes. Whether a dilaton can be still compatible with current data is relegated to an appendix.

On the decoupling of mirror fermions

An approach to the formulation of chiral gauge theories on the lattice is to start with a vector-like theory, but decouple one chirality (the "mirror" fermions) using strong Yukawa interactions with a chirally coupled "Higgs" field. While this is an attractive idea, its viability needs to be tested with nonperturbative studies. The model that we study here, the so-called "3-4-5" model, is anomaly free and the presence of massless states in the mirror sector is not required by anomaly matching arguments, in contrast to the "1-0" model that was studied previously. We have computed the polarization tensor in this theory and find a directional discontinuity that appears to be nonzero in the limit of an infinite lattice, which is equivalent to the continuum limit at fixed physical volume. We show that a similar behavior occurs for the free massless Ginsparg-Wilson fermion, where the polarization tensor is known to have a directional discontinuity in the continuum limit. We thus find support for the conclusion that in the continuum limit of the 3-4-5 model, there are massless charged modes in the mirror sector so that it does not decouple from the light sector. The value of the discontinuity we obtain allows for two interpretations: either a chiral gauge theory does not emerge and mirror-sector fermions in a chiral anomaly free representation remain massless, or a massless vectorlike mirror fermion appears. We end by discussing some questions for future study.

Bootstrap Dynamical Symmetry Breaking

Despite the emergence of a 125 GeV Higgs-like particle at the LHC, we explore the possibility of dynamical electroweak symmetry breaking by strong Yukawa coupling of very heavy new chiral quarksQ. Taking the 125 GeV object to be a dilaton with suppressed couplings, we note that the Goldstone bosonsGexist as longitudinal modesVLof the weak bosons and would couple toQwith Yukawa couplingλQ. WithmQ≳700 GeV from LHC, the strongλQ≳4could lead to deeply boundQQ¯states. We postulate that the leading “collapsed state,” the color-singlet (heavy) isotriplet, pseudoscalarQQ¯mesonπ1, isGitself, and a gap equation without Higgs is constructed. Dynamical symmetry breaking is affected via strongλQ, generatingmQwhile self-consistently justifying treatingGas massless in the loop, hence, “bootstrap,” Solving such a gap equation, we find thatmQshould be several TeV, orλQ≳4π, and would become much heavier if there is a light Higgs boson. For such heavy chiral quarks, we find analogy with theπ−Nsystem, by which we conjecture the possible annihilation phenomena ofQQ¯→nVLwith high multiplicity, the search of which might be aided by Yukawa-boundQQ¯resonances.

Incorporating fermions in the Gaussian effective potential: The Higgs-top sector

The Higgs-Top model is studied by a non-perturbative variational extension of the Gaussian Effective Potential that incorporates fermions. In the limit of a very strong Yukawa coupling the one-loop result is shown to follow a single-parameter scaling while the gaussian fluctuations give rise to important deviations from scaling and to a reduction of the vev and of the top mass. A good general agreement is found with lattice data when a comparison can be made. The vacuum is shown to be stable for any choice of the Yukawa coupling, at variance with renormalized perturbation theory. Analytical results are provided for few observables like the renormalized mass of the Higgs boson and its wave function renormalization constant. Extensions to gauge theories like QCD are briefly discussed.

Searching for new heavy chiral quark pairs via their annihilation to multiple vector bosons

Drawing analogy of replacing the nucleon by heavy chiral quark $Q$, the pion by Goldstone boson $G$, and $\pi NN$ coupling by $GQQ$ coupling, we construct a statistical model for $Q\bar Q \to nG$ annihilation, i.e. into $n$ longitudinal weak bosons. This analogy is becoming prescient since the LHC direct bound $m_Q > 611$ GeV implies strong Yukawa coupling. Taking $m_Q \in (1, 2)$ TeV, the mean number $<n_G>$ ranges from 6 to over 10, with negligible two or three boson production. With individual $t'$ or $b'$ decays suppressed either by phase space or quark mixing, and given the strong Yukawa coupling, $Q\bar Q\to nV_L$ is the likely outcome for very heavy $Q\bar Q$ production at the LHC.

Dynamical symmetry breaking in models with strong Yukawa interactions

Dynamical symmetry breaking in models with strong Yukawa interactionsThe primary aim of this paper is to explore the possibility of spontaneous symmetry breaking by strong Yukawa dynamics. Technically, the symmetry is assumed to be broken by formation of symmetry-breaking parts of both the scalar and the fermion propagators, rather than by the scalar vacuum expectation values. The idea is first introduced on an example of a toy model with the underlying symmetry being an Abelian one and later applied to a realistic model of electroweak interaction. In addition, the paper also deals with some more general, model-independent issues, applicable not only to the discussed model of strong Yukawa dynamics, but to a wider class of models with dynamical mass generation. First of these issues is the problem of fermion flavor mixing in the presence of fermion self-energies with a general momentum dependence. It is in particular shown how to define the Cabibbo-Kobayashi-Maskawa matrix in such models and argued that it can come out in principle non-unitary. Second issue is the problem of calculating the gauge boson masses when the symmetry is broken by fermion self-energies. On top of deriving the formula for the gauge boson mass matrix we also find corrections to the related Pagels-Stokar formula.

Early LHC phenomenology of Yukawa-bound heavyQQ¯mesons

Current limits from the LHC on fourth generation quarks are already at the unitarity bound of 500 GeV or so. If they exist, the strong Yukawa couplings are turning nonperturbative, and may form bound states. We study the domain of m_{b'} and m_{t'} in the range of 500 to 700 GeV, where we expect binding energies are mainly of Yukawa origin, with QCD subdominant. To be consistent with electroweak precision tests, the t' and b' quarks have to be nearly degenerate, exhibiting a new "isospin". Comparing relativistic expansion with a relativistic bound state approach, we find the most interesting is the production of a color octet, isosinglet vector meson (a "gluon-prime") via q\bar{q} to \omega_8. Leading decay modes are \pi_8^\pm W^\mp, \pi_8^0Z^0, and constituent quark decay, with q\bar{q} and t\bar{t}' and b\bar{b}' subdominant. The color octet, isovector pseudoscalar \pi_8 meson decays via constituent quark decay, or to Wg. These decay rates are parameterized by the decay constant, the binding energy and mass differences, and V_{tb'}. For small V_{t'b}, one could have a spectacular signal of WWg, where a soft W accompanies a very massive Wg pair. In general, however, one has high multiplicity signals with b, W and t jet substructures that are not so different from t'\bar{t}' and b'\bar{b}' search.

Vapor–liquid surface tension of strong short-range Yukawa fluid

The thermodynamic properties of strong short-range attractive Yukawa fluids, κ = 10, 9, 8, and 7, are determined by combining the slab technique with the standard and the replica exchange Monte Carlo (REMC) methods. A good agreement was found among the coexistence curves of these systems calculated by REMC and those previously reported in the literature. However, REMC allows exploring the coexistence at lower temperatures, where dynamics turns glassy. To obtain the surface tension we employed, for both methods, a procedure that yields the pressure tensor components for discontinuous potentials. The surface tension results obtained by the standard MC and REMC techniques are in good agreement.

Renormalization group fixed point with a fourth generation: Higgs-induced bound states and condensates

In the Standard Model with four generations, the two-loop renormalization group equations for the Higgs quartic and Yukawa couplings show a quasi fixed point structure which does not appear at the one-loop level. This quasi fixed point behavior indicates a possible restoration of scale symmetry above some physical cut-off scale Λ FP . We conjecture that there exists a true fixed point which is reached at a similar energy scale. If the masses of the fourth family are sufficiently large, this cut-off scale, Λ FP , is situated in the range of a few TeV to the order of 10 2 TeV , above which the Higgs quartic and Yukawa couplings become practically constant. We found that around Λ FP the strong Yukawa couplings make it possible for the fourth generation to form bound states, including composite extra Higgs doublets. In this scenario the fourth generation condensates are obtained without introducing Technicolor or other unknown interactions.

Dynamical electroweak symmetry breaking due to strong Yukawa interactions

We present a new mechanism for electroweak symmetry breaking (EWSB) based on a strong Yukawa dynamics. We consider an SU(2)L × U(1)Y gauge invariant model endowed with the usual Standard Model fermion multiplets and with two massive scalar doublets. We show that, unlike in the Standard Model, EWSB is possible even with vanishing vacuum expectation values of the scalars. Such EWSB is achieved dynamically by means of the (presumably strong) Yukawa couplings and manifests itself by the emergence of fermion and gauge boson masses and scalar mass splittings, which are expressed in a closed form in terms of the fermion and scalar proper self-energies. The ‘would-be’ Nambu–Goldstone bosons are shown to be composites of both the fermions and the scalars. We demonstrate that the simplest version of the model is compatible with basic experimental constraints.

Lattice chirality, anomaly matching, and more on the (non)decoupling of mirror fermions

We study 't Hooft anomaly matching in lattice models with strong Yukawa or multi-fermion interactions. Strong non-gauge interactions among the mirror fermions in a vectorlike lattice gauge theory are introduced with the aim to obtain, in a strong-coupling symmetric phase, a long-distance unbroken gauge theory with chiral fermions in a complex representation. We show how to use exact lattice chirality to analyze the anomaly matching conditions on chiral symmetry current correlators at finite lattice spacing and volume. We perform a Monte Carlo study of the realization of anomaly matching in a toy two-dimensional model with an anomalous mirror-fermion content at strong mirror Yukawa coupling. We show that 't Hooft anomaly matching is satisfied, in most of the phase diagram, via the minimal solution in either the massless fermion or ``Goldstone mode, while in some cases there are extra massless vectorlike mirror fermions. The mirror spectrum at strong coupling is thus consistent with long-distance unitarity. We discuss the implications of our results for future studies of the most interesting case of the decoupling of anomaly-free mirror-fermion sectors.