scholarly journals Anomalies and accidental symmetries: charging the scalar leptoquark under Lμ − Lτ

2020 ◽  
Vol 2020 (12) ◽  
Author(s):  
Joe Davighi ◽  
Matthew Kirk ◽  
Marco Nardecchia
Keyword(s):  
Higgs Mass ◽  
Tree Level ◽  
Global Symmetry ◽  
Direct Role ◽  
Quantum Numbers ◽  
Scalar Leptoquark ◽  
The Standard Model ◽  
Flavour Violation ◽  
Conceptual Problems ◽  
Symmetry Structure

Abstract While the S3 scalar leptoquark presents a possible tree-level explanation of the b → sℓℓ flavour anomalies, it suffers from two conceptual problems which are often disregarded by model-builders. Firstly, the quantum numbers of the S3 allow for a renormalisable diquark operator that would trigger rapid proton decay unless its coupling were tuned away. Secondly, one expects the leptoquark to have generic couplings to leptons, which require tuning to avoid stringent experimental bounds on lepton flavour violation. By gauging a U(1) current that acts as Lμ− Lτ on the Standard Model (SM) fermions, and under which the leptoquark has charge −1, one can remedy both these problems. The additional U(1), which is spontaneously broken at some high scale, is associated with a massive Z′ gauge boson and a scalar SM singlet Φ, which play no direct role in mediating the anomalous B meson decays. By computing one- and two-loop mass corrections, we show that this pair of particles can be hidden away at much higher mass scales without destabilising either the Higgs or the leptoquark masses. The only low-energy relic of gauging Lμ− Lτ is thus the accidental global symmetry structure of the lagrangian. On the other hand, we find quite generally that an S3 leptoquark that mediates the b → sℓℓ anomalies cannot be much heavier than a few TeV without itself inducing large Higgs mass corrections.

scholarly journals Causality, unitarity and symmetry in effective field theory

2021 ◽  
Vol 2021 (7) ◽  
Author(s):  
Timothy Trott
Keyword(s):  
Effective Field ◽  
Tree Level ◽  
Global Symmetry ◽  
Fundamental Limits ◽  
Effective Interactions ◽  
Effective Contact ◽  
Higher Dimensional ◽  
Forward Limit ◽  
Mass Dimension ◽  
Flavour Violation

Abstract Sum rules in effective field theories, predicated upon causality, place restrictions on scattering amplitudes mediated by effective contact interactions. Through unitarity of the S-matrix, these imply that the size of higher dimensional corrections to transition amplitudes between different states is bounded by the strength of their contributions to elastic forward scattering processes. This places fundamental limits on the extent to which hypothetical symmetries can be broken by effective interactions. All analysis is for dimension 8 operators in the forward limit. Included is a thorough derivation of all positivity bounds for a chiral fermion in SU(2) and SU(3) global symmetry representations resembling those of the Standard Model, general bounds on flavour violation, new bounds for interactions between particles of different spin, inclusion of loops of dimension 6 operators and illustration of the resulting strengthening of positivity bounds over tree-level expectations, a catalogue of supersymmetric effective interactions up to mass dimension 8 and 4 legs and the demonstration that supersymmetry unifies the positivity theorems as well as the new bounds.

scholarly journals STRING SCALE GAUGE COUPLING UNIFICATION WITH VECTOR-LIKE EXOTICS AND NONCANONICAL U(1)Y NORMALIZATION

2007 ◽  
Vol 22 (32) ◽  
pp. 6203-6218 ◽  
Author(s):  
V. BARGER ◽  
JING JIANG ◽  
PAUL LANGACKER ◽  
TIANJUN LI
Keyword(s):  
Standard Model ◽  
Gauge Coupling ◽  
Independent Sets ◽  
Tree Level ◽  
New Approach ◽  
Quantum Numbers ◽  
The Standard Model

We use a new approach to study string scale gauge coupling unification systematically, allowing both the possibility of noncanonical U (1)Y normalization and the existence of vector-like particles whose quantum numbers are the same as those of the Standard Model (SM) fermions and their Hermitian conjugates and the SM adjoint particles. We first give all the independent sets (Yi) of particles that can be employed to achieve SU (3)C and SU (2)L string scale gauge coupling unification and calculate their masses. Second, for a noncanonical U (1)Y normalization, we obtain string scale SU (3)C × SU (2)L × U (1)Y gauge coupling unification by choosing suitable U (1)Y normalizations for each of the Yi sets. Alternatively, for the canonical U (1)Y normalization, we achieve string scale gauge coupling unification by considering suitable combinations of the Yi sets or by introducing additional independent sets (Zi), that do not affect the SU (3)C × SU (2)L unification at tree level, and then choosing suitable combinations, one from the Yi sets and one from the Zi sets. We also briefly discuss string scale gauge coupling unification in models with higher Kac–Moody levels for SU (2)L or SU (3)C.

scholarly journals CONSTRAINTS ON A GENERAL HIGGS SECTOR FROM $K^0 - \tilde K^0$, $B_d - \bar B_d$ MIXING AND THE ε PARAMETER

1996 ◽  
Vol 11 (08) ◽  
pp. 675-686 ◽  
Author(s):  
DEBRUPA CHAKRAVERTY ◽  
ANIRBAN KUNDU
Keyword(s):  
Standard Model ◽  
Higgs Mass ◽  
Higgs Sector ◽  
Tree Level ◽  
Text Data ◽  
Mixing Angle ◽  
Stringent Constraint ◽  
The Standard Model ◽  
Charged Higgs ◽  
Scalar Sector

The scalar sector of the standard model is extended to include an arbitrary assortment of scalars. In the case where this assignment does not preserve p=1 at the tree-level, the departure from unity itself puts the most stringent constraint on the scalar sector, and where ptree=1 is maintained, useful bounds on the parameter space of the charged Higgs mass and the doublet-nondoublet mixing angle can arise from data on [Formula: see text], [Formula: see text] mixing and the ε parameter. These constraints turn out to be comparable (and in some cases, better) to those obtained from [Formula: see text] data.

QUASI SUPERSYMMETRY WITHIN THE STANDARD MODEL AND HIGGS MASS

1999 ◽  
Vol 14 (35) ◽  
pp. 2447-2452
Author(s):  
B. B. DEO ◽  
L. P. SINGH
Keyword(s):  
Standard Model ◽  
Top Quark ◽  
Degrees Of Freedom ◽  
Higgs Mass ◽  
Higgs Bosons ◽  
Tree Level ◽  
Mass Relation ◽  
The Standard Model ◽  
A Charge ◽  
Higgs Fields

The 12 bosonic degrees of freedom of the standard model (SM) are exactly matched by fermionic degrees of freedom of a single colored quark, e.g. top. Indeed, we construct a charge involving top-quark, gauge and Higgs fields which satisfy usual supersymmetry algebra. The colored quark states behave like the superpartners of gauge and Higgs bosons and vice versa. When this SUSY is broken, a mass relation must be satisfied at the tree level from which the mass of the Higgs is predicted to be 300.5±11 GeV.

scholarly journals Higgs flavor phenomenology in a supersymmetric left-right model with parity

2021 ◽  
Vol 2021 (6) ◽  
Author(s):  
Syuhei Iguro ◽  
Junichiro Kawamura ◽  
Yuji Omura ◽  
Yoshihiro Shigekami
Keyword(s):  
Higgs Mass ◽  
Fine Tuning ◽  
Tree Level ◽  
Supersymmetric Model ◽  
Parameter Region ◽  
Yukawa Couplings ◽  
Lepton Flavor ◽  
Flavor Changing ◽  
Fermion Masses ◽  
The Standard Model

Abstract In this paper, we focus on the supersymmetric model with left-right (LR) symmetry, that is especially proposed in our previous work [1]. In this model, there are four Higgs doublets in order to realize the Standard Model (SM) fermion masses and the Cabibbo-Kobayashi-Maskawa matrix. The heavy Higgs doublets unavoidably have flavor changing couplings to the SM fermions and induce flavor-changing neutral currents at tree level. We study broader parameter space than the previous work with including the renormalization group corrections to the Yukawa couplings between the LR breaking scale, $$ \mathcal{O} $$ O (1013) GeV, and the supersymmetry breaking scales, $$ \mathcal{O} $$ O (100) TeV. The CP violating observable in K–$$ \overline{K} $$ K ¯ mixing, ϵK, strongly constrains the model, so that heavy Higgs mass should be heavier than $$ \mathcal{O} $$ O (100) TeV. We study the lepton flavor violating (LFV) processes setting heavy Higgs masses to be 170 TeV. The branching ratios of μ → 3e and the μ–e conversion can be larger than 10−16 that could be covered by the future experiments. We also study the degree of fine-tuning in the parameter region that predicts testable LFV processes.

scholarly journals The impact of flavour data on global fits of the MFV SMEFT

2020 ◽  
Vol 2020 (12) ◽  
Author(s):  
Rafael Aoude ◽  
Tobias Hurth ◽  
Sophie Renner ◽  
William Shepherd
Keyword(s):  
Initial Conditions ◽  
New Physics ◽  
Effective Field ◽  
Tree Level ◽  
Minimal Flavour Violation ◽  
The Standard Model ◽  
Flavour Violation ◽  
Stringent Test ◽  
Global Fit ◽  
The Impact

Abstract We investigate the information that can be gained by including flavour data in fits of the Standard Model Effective Field Theory (SMEFT) with the assumption of Minimal Flavour Violation (MFV), allowing — as initial conditions at the high scale — leading terms in spurionic Yukawas only. Starting therefore from a theory with no tree level flavour changing neutral currents at the scale of new physics, we calculate effects in flavour changing processes at one loop, and the resulting constraints on linear combinations of SMEFT coefficients, consistently parameterising the electroweak parameters and the CKM within the SMEFT. By doing a global fit including electroweak, Higgs and low energy precision measurements among others, we show that flavour observables put strong constraints on previously unconstrained operator directions. The addition of flavour data produces four independent constraints at order TeV or above on otherwise flat directions; reducing to three when complete U(3)5 flavour symmetry is assumed. Our findings demonstrate that flavour remains a stringent test for models of new physics, even in the most flavourless scenario.

Tree-level unitarity violation for large Higgs mass in a supersymmetric extension of the standard model

1987 ◽  
Vol 191 (4) ◽  
pp. 409-415 ◽  
Author(s):  
R. Casalbuoni ◽  
D. Dominici ◽  
F. Feruglio ◽  
R. Gatto
Keyword(s):  
Standard Model ◽  
Higgs Mass ◽  
Tree Level ◽  
Supersymmetric Extension ◽  
The Standard Model

scholarly journals Interplay of New Physics effects in (g − 2)ℓ and h → ℓ+ℓ− — lessons from SMEFT

2021 ◽  
Vol 2021 (6) ◽  
Author(s):  
Svjetlana Fajfer ◽  
Jernej F. Kamenik ◽  
M. Tammaro
Keyword(s):  
Closed Operator ◽  
Higgs Doublet ◽  
New Physics ◽  
Effective Field ◽  
Tree Level ◽  
Electroweak Symmetry ◽  
Scalar Leptoquark ◽  
Doublet Model ◽  
The One ◽  
Two Higgs Doublet Model

Abstract We explore the interplay of New Physics (NP) effects in (g− 2)ℓ and h→ℓ+ℓ− within the Standard Model Effective Field Theory (SMEFT) framework, including one-loop Renormalization Group (RG) evolution of the Wilson coefficients as well as matching to the observables below the electroweak symmetry breaking scale. We include both the leading dimension six chirality flipping operators including a Higgs and SU(2)L gauge bosons as well as four-fermion scalar and tensor operators, forming a closed operator set under the SMEFT RG equations. We compare present and future experimental sensitivity to different representative benchmark scenarios. We also consider two simple UV completions, a Two Higgs Doublet Model and a single scalar LeptoQuark extension of the SM, and show how tree level matching to SMEFT followed by the one-loop RG evolution down to the electroweak scale can reproduce with high accuracy the (g−2)ℓ and h→ℓ+ℓ− contributions obtained by the complete one- and even two-loop calculations in the full models.

scholarly journals A composite Higgs with a heavy composite axion

2020 ◽  
Vol 2020 (12) ◽  
Author(s):  
Tony Gherghetta ◽  
Minh D. Nguyen
Keyword(s):  
Cp Violation ◽  
Gauge Group ◽  
Scalar Fields ◽  
Higgs Model ◽  
Global Symmetry ◽  
Color Group ◽  
High Scale ◽  
Axion Mass ◽  
Composite Higgs ◽  
The Standard Model

Abstract We consider the strong dynamics associated with a composite Higgs model that simultaneously produces dynamical axions and solves the strong CP problem. The strong dynamics arises from a new Sp or SU(4) hypercolor gauge group containing QCD colored hyperfermions that confines at a high scale. The hypercolor global symmetry is weakly gauged by the Standard Model electroweak gauge group and an enlarged color group, SU(N + 3) × SU(N)′. When hyperfermion condensates form, they not only lead to an SU(5)/SO(5) composite Higgs model but also spontaneously break the enlarged color group to SU(3)c× SU(N)D. At lower energies, the SU(N)D group confines, producing two dynamical axions that eliminates all CP violation. Furthermore, small instantons from the SU(N)′ group can enhance the axion mass, giving rise to TeV scale axion masses that can be detected at collider experiments. Our model provides a way to unify the composite Higgs with dynamical axions, without introducing new elementary scalar fields, while also extending the range of axion masses that addresses the strong CP problem.

scholarly journals Lowering the scale of Pati-Salam breaking through seesaw mixing

2021 ◽  
Vol 2021 (5) ◽  
Author(s):  
Matthew J. Dolan ◽  
Tomasz P. Dutka ◽  
Raymond R. Volkas
Keyword(s):  
Degrees Of Freedom ◽  
Tree Level ◽  
Charged Current ◽  
Meson Decay ◽  
Neutrino Masses ◽  
Down Quark ◽  
The Standard Model ◽  
Decay Widths ◽  
Left And Right ◽  
Charged Leptons

Abstract We analyse the experimental limits on the breaking scale of Pati-Salam extensions of the Standard Model. These arise from the experimental limits on rare-meson decay processes mediated at tree-level by the vector leptoquark in the model. This leptoquark ordinarily couples to both left- and right-handed SM fermions and therefore the meson decays do not experience a helicity suppression. We find that the current limits vary from $$ \mathcal{O} $$ O (80–2500) TeV depending on the choice of matrix structure appearing in the relevant three-generational charged-current interactions. We extensively analyse scenarios where additional fermionic degrees of freedom are introduced, transforming as complete Pati-Salam multiplets. These can lower the scales of Pati-Salam breaking through mass-mixing within the charged-lepton and down-quark sectors, leading to a helicity suppression of the meson decay widths which constrain Pati-Salam breaking. We find four multiplets with varying degrees of viability for this purpose: an SU(2)L/R bidoublet, a pair of SU(4) decuplets and either an SU(2)L or SU(2)R triplet all of which contain heavy exotic versions of the SM charged leptons. We find that the Pati-Salam limits can be as low as $$ \mathcal{O} $$ O (5–150) TeV with the addition of these four multiplets. We also identify an interesting possible connection between the smallness of the neutrino masses and a helicity suppression of the Pati-Salam limits for three of the four multiplets.

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