Question: Put constraint on symbolic calculation

Hi everyone, I have some symbolic expressions as below:



Zeta := phi+(Ems+I*Eml)/(Ef-Ems-I*Eml)+(3*(1-phi))*((1-g)*alpha^2-(1/2)*g)/(alpha^2-1): 

g := (1/2)*Pi*alpha:

Lambda := (1-phi)*((3*(alpha^2+.25))*g-2*alpha^2)/(alpha^2-1): 

Ec := (Ems+I*Eml)/(1-(1/4)*phi*(1/Zeta+3/(Zeta+Lambda))):

a := simplify(Re(Ec)), assuming positive;

the output of the code maple gives me as 'a' is very long and boring! Therefore I want to make it shorter. Since (alpha<<1), I want to set a constraint as (alpha^(2 and more than 2)=0). How can I put that constraint on the output? thanks

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