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Physlib.Particles.StandardModel.HiggsBoson.EffectivePotential

The effective potential of the Higgs field

We define a general effective potential for the Higgs field. For this we define two properties of the potential: invariance under the gauge group, and a maximum mass dimension.

Given these, we prove that the potential can be expressed as a polynomial in the norm of the Higgs field.

A. The invariance of the general potential under the gauge group

B. Maximum mass dimension

C. Terms of a given mass dimension

D. Potential in terms of the norm of the Higgs field

18 declarations

abbrev

Effective potential of the Higgs field

The type of general effective potentials for the Higgs field, defined as the set of real-valued functions V:HiggsVecRV: \text{HiggsVec} \to \mathbb{R}, where HiggsVec\text{HiggsVec} is the 2-dimensional complex vector space C2\mathbb{C}^2.

definition

Gauge invariance of the effective potential V(gϕ)=V(ϕ)V(g \cdot \phi) = V(\phi)

The property `IsInvariant` defines the gauge symmetry of an effective potential V:C2RV: \mathbb{C}^2 \to \mathbb{R}. It states that for every element gg in the Standard Model gauge group G=SU(3)×SU(2)×U(1)\mathcal{G} = SU(3) \times SU(2) \times U(1) and every Higgs field value ϕC2\phi \in \mathbb{C}^2, the potential remains unchanged under the gauge action: V(gϕ)=V(ϕ) V(g \cdot \phi) = V(\phi) where the action gϕg \cdot \phi is defined by the transformation g13(g2ϕ)g_1^3 (g_2 \phi) with g2SU(2)g_2 \in SU(2) and g1U(1)g_1 \in U(1).

theorem

A Gauge Invariant Higgs Potential VV Factors Through the Norm ϕ\|\phi\|

Let V:C2RV: \mathbb{C}^2 \to \mathbb{R} be an effective potential of the Higgs field. If VV is gauge invariant (meaning V(gϕ)=V(ϕ)V(g \cdot \phi) = V(\phi) for all elements gg of the Standard Model gauge group G\mathcal{G}), then there exists a function f:RRf: \mathbb{R} \to \mathbb{R} such that V=fV = f \circ \|\cdot\|, or equivalently V(ϕ)=f(ϕ)V(\phi) = f(\|\phi\|) for all ϕC2\phi \in \mathbb{C}^2, where \|\cdot\| denotes the standard Euclidean norm on C2\mathbb{C}^2.

definition

The Higgs potential VV has mass dimension n\le n

The effective potential V:HiggsVecRV: \text{HiggsVec} \to \mathbb{R} is said to have a maximum mass dimension less than or equal to nn if there exists a real multivariate polynomial pp in four variables such that for every ϕHiggsVec\phi \in \text{HiggsVec}, the potential V(ϕ)V(\phi) is equal to the evaluation of pp on the four real components of ϕ\phi, and the total degree of pp is at most nn. Here, HiggsVec\text{HiggsVec} is the 2-dimensional complex vector space C2\mathbb{C}^2 representing the Higgs doublet.

definition

Multivariate polynomial pp associated with a Higgs potential VV of mass dimension n\le n

Given an effective potential V:HiggsVecRV: \text{HiggsVec} \to \mathbb{R} that has a maximum mass dimension at most nn, where HiggsVecC2\text{HiggsVec} \cong \mathbb{C}^2 is the 2-dimensional complex vector space of the Higgs field, this definition provides the corresponding multivariate polynomial pR[x1,x2,x3,x4]p \in \mathbb{R}[x_1, x_2, x_3, x_4] in four real variables. This polynomial represents the potential such that V(ϕ)=p(Re(ϕ1),Im(ϕ1),Re(ϕ2),Im(ϕ2))V(\phi) = p(\text{Re}(\phi_1), \text{Im}(\phi_1), \text{Re}(\phi_2), \text{Im}(\phi_2)), and its total degree is at most nn.

theorem

The total degree of a Higgs potential with mass dimension n\le n is at most nn

Let VV be an effective potential for the Higgs field ϕHiggsVecC2\phi \in \text{HiggsVec} \cong \mathbb{C}^2. If VV has a maximum mass dimension at most nNn \in \mathbb{N}, then the total degree of its corresponding real multivariate polynomial p(x1,x2,x3,x4)p(x_1, x_2, x_3, x_4) satisfies deg(p)n\text{deg}(p) \le n.

theorem

V(ϕ)V(\phi) Equals the Evaluation of its Associated Polynomial

Let V:HiggsVecRV: \text{HiggsVec} \to \mathbb{R} be an effective potential of the Higgs field with maximum mass dimension at most nNn \in \mathbb{N}, and let pp be its associated multivariate polynomial in four real variables. For any Higgs doublet ϕHiggsVec\phi \in \text{HiggsVec}, the value of the potential V(ϕ)V(\phi) is equal to the evaluation of the polynomial pp on the four real components of ϕ\phi, namely (Re(ϕ1),Im(ϕ1),Re(ϕ2),Im(ϕ2))(\text{Re}(\phi_1), \text{Im}(\phi_1), \text{Re}(\phi_2), \text{Im}(\phi_2)).

definition

Mass dimension mm term of the Higgs potential VV

Given an effective potential V:HiggsVecRV: \text{HiggsVec} \to \mathbb{R} with a maximum mass dimension at most nn, where HiggsVecC2\text{HiggsVec} \cong \mathbb{C}^2 is the space of the Higgs doublet, the function `termOfMassDim V h m` represents the part of the potential with exactly mass dimension mNm \in \mathbb{N}. It is defined by taking the mm-th homogeneous component of the multivariate polynomial pR[x1,x2,x3,x4]p \in \mathbb{R}[x_1, x_2, x_3, x_4] associated with VV and evaluating it on the four real components of the Higgs field ϕ=(ϕ1,ϕ2)C2\phi = (\phi_1, \phi_2) \in \mathbb{C}^2.

theorem

The mass dimension mm term of the Higgs potential is 00 for m>nm > n

Let V:HiggsVecRV: \text{HiggsVec} \to \mathbb{R} be an effective potential of the Higgs field with maximum mass dimension at most nNn \in \mathbb{N}, where HiggsVecC2\text{HiggsVec} \cong \mathbb{C}^2. If mm is a natural number such that n<mn < m, then the term of mass dimension mm of the potential VV (denoted as `termOfMassDim V h m`) is zero for any Higgs doublet ϕHiggsVec\phi \in \text{HiggsVec}.

theorem

Homogeneity of the mass dimension mm term of the Higgs potential VV

Let VV be an effective potential of the Higgs field with maximum mass dimension at most nn. For any natural number mm, the term of mass dimension mm of the potential, denoted as VmV_m, is homogeneous of degree mm. That is, for any Higgs field vector ϕHiggsVec\phi \in \text{HiggsVec} and real scalar tRt \in \mathbb{R}, Vm(tϕ)=tmVm(ϕ).V_m(t \phi) = t^m V_m(\phi).

theorem

The Higgs potential VV equals the sum of its mass dimension terms VmV_m up to its maximum dimension nn.

Let V:HiggsVecRV: \text{HiggsVec} \to \mathbb{R} be an effective potential for the Higgs field, where HiggsVecC2\text{HiggsVec} \cong \mathbb{C}^2 is the 2-dimensional complex vector space of the Higgs doublet. If VV has a maximum mass dimension at most nNn \in \mathbb{N} (i.e., it can be represented as a polynomial of degree at most nn in the real components of the field), then for any ϕHiggsVec\phi \in \text{HiggsVec}, the potential is equal to the sum of its terms of mass dimension mm for m{0,,n}m \in \{0, \dots, n\}: V(ϕ)=m=0nVm(ϕ)V(\phi) = \sum_{m=0}^n V_m(\phi) where VmV_m denotes the component of the potential with exactly mass dimension mm.

theorem

Expansion of the scaled Higgs potential V(tϕ)V(t\phi) into mass dimension terms

Let V:HiggsVecRV: \text{HiggsVec} \to \mathbb{R} be an effective potential of the Higgs field with maximum mass dimension less than or equal to nn, where HiggsVecC2\text{HiggsVec} \cong \mathbb{C}^2. For any Higgs field vector ϕHiggsVec\phi \in \text{HiggsVec} and any real scalar tRt \in \mathbb{R}, the potential evaluated at the scaled field tϕt \phi satisfies V(tϕ)=m=0ntmVm(ϕ)V(t \phi) = \sum_{m=0}^{n} t^m V_m(\phi) where VmV_m denotes the mm-th mass dimension term of the potential VV.

theorem

Gauge Invariance of the Mass Dimension mm Term of the Higgs Potential

Suppose V:C2RV: \mathbb{C}^2 \to \mathbb{R} is an effective Higgs potential with a maximum mass dimension at most nn. If VV is gauge invariant, meaning V(gϕ)=V(ϕ)V(g \cdot \phi) = V(\phi) for all elements gg of the gauge group G=SU(3)×SU(2)×U(1)\mathcal{G} = SU(3) \times SU(2) \times U(1) and Higgs fields ϕC2\phi \in \mathbb{C}^2, then for any mNm \in \mathbb{N}, the term of the potential with mass dimension mm is also gauge invariant.

theorem

The mm-th mass dimension term of a gauge-invariant Higgs potential satisfies Vm(ϕ)=cϕmV_m(\phi) = c \|\phi\|^m

Let V:C2RV: \mathbb{C}^2 \to \mathbb{R} be an effective potential for the Higgs field with a maximum mass dimension at most nn. If VV is gauge invariant under the Standard Model gauge group, then for any mNm \in \mathbb{N}, there exists a constant cRc \in \mathbb{R} such that for every Higgs field value ϕC2\phi \in \mathbb{C}^2, the term of mass dimension mm in the potential, denoted Vm(ϕ)V_m(\phi), is given by Vm(ϕ)=cϕm V_m(\phi) = c \|\phi\|^m where ϕ\|\phi\| is the norm of the Higgs doublet in the 2-dimensional complex vector space C2\mathbb{C}^2.

theorem

Odd mass dimension terms of a gauge-invariant Higgs potential are zero

Let V:C2RV: \mathbb{C}^2 \to \mathbb{R} be an effective potential of the Higgs field that is gauge-invariant and has maximum mass dimension at most nn. For any odd natural number mm, the term of mass dimension mm in the potential vanishes for all ϕC2\phi \in \mathbb{C}^2, i.e., Vm(ϕ)=0. V_m(\phi) = 0.

theorem

An Invariant Higgs Potential equals the Sum of its Even Mass Dimension Terms

Let V:C2RV: \mathbb{C}^2 \to \mathbb{R} be an effective Higgs potential. Suppose VV is invariant under the gauge group action (i.e., V(gϕ)=V(ϕ)V(g \cdot \phi) = V(\phi) for all gSU(2)×U(1)g \in SU(2) \times U(1)) and has a maximum mass dimension less than or equal to nn (meaning VV is a polynomial in the real components of the Higgs field ϕ\phi with total degree at most nn). Then, for any ϕC2\phi \in \mathbb{C}^2, the potential V(ϕ)V(\phi) is equal to the sum of its homogeneous components of even mass dimension 2m2m: V(ϕ)=m=0n/2V2m(ϕ)V(\phi) = \sum_{m=0}^{\lfloor n/2 \rfloor} V_{2m}(\phi) where V2m(ϕ)V_{2m}(\phi) denotes the part of the potential with exactly mass dimension 2m2m.

theorem

Gauge Invariant Higgs Potential equals the Sum of its Even Mass Dimension Terms

Let V:C2RV: \mathbb{C}^2 \to \mathbb{R} be an effective potential for the Higgs field. Suppose VV is invariant under the gauge group action and has a maximum mass dimension at most nn. For any ϕC2\phi \in \mathbb{C}^2, the potential V(ϕ)V(\phi) can be expressed as the sum of its terms with even mass dimension 2m2m for m{0,1,,n/2}m \in \{0, 1, \dots, \lfloor n/2 \rfloor\}: V(ϕ)=m=0n/2V2m(ϕ)V(\phi) = \sum_{m=0}^{\lfloor n/2 \rfloor} V_{2m}(\phi) where V2mV_{2m} denotes the part of the potential with exactly mass dimension 2m2m.

theorem

An invariant Higgs potential with mass dimension n\le n is a sum of even powers of ϕ\|\phi\|

Let V:C2RV: \mathbb{C}^2 \to \mathbb{R} be an effective potential for the Higgs field. Suppose VV is invariant under the gauge group action (i.e., V(gϕ)=V(ϕ)V(g \cdot \phi) = V(\phi) for all gSU(2)×U(1)g \in SU(2) \times U(1)) and has a maximum mass dimension less than or equal to nn (meaning VV is a polynomial in the real components of the Higgs field ϕ\phi with total degree at most nn). Then, for any ϕC2\phi \in \mathbb{C}^2, there exist real coefficients cmc_m for m{0,1,,n/2}m \in \{0, 1, \dots, \lfloor n/2 \rfloor\} such that the potential can be expressed as a sum of even powers of the norm ϕ\|\phi\|: V(ϕ)=m=0n/2cmϕ2mV(\phi) = \sum_{m=0}^{\lfloor n/2 \rfloor} c_m \|\phi\|^{2m}