Gauge Coupling Unification: Strings versus SUSY-GUTs

Abstract

Standard (level one) heterotic string models with standard model gauge group predict the unification of $SU(3)$ and $SU(2)$ gauge couplings whereas the $U(1)$ factor is unified modulo an unknown normalization factor $k_1$. On the other hand the unification mass is known. I argue that this situation is quite analogous (though opposite) to that in SUSY-GUTs in which the $U(1)$ normalization is known ($k_1=5/3$) but the unification mass $M_X$ is unknown. I emphasize that $k_1$ should be taken as a free parameter in the string approach (quite in the same way as $M_X$ is taken as a free parameter in SUSY-GUTs). If this is done, the success of the string approach concerning gauge coupling unification is comparable to that in SUSY-GUTs

7 pages (1 figure available upon request, either as PS file or hard copy) FTUAM-35-93 harvmac

References in corpus (2)

• Uncertainties in Coupling Constant Unification
• Computing the Weak Mixing Angle from Anomaly Cancellation

Cited by in corpus (43)

• Axions In String Theory
• Strong Coupling Expansion Of Calabi-Yau Compactification
• String Theory and the Path to Unification: A Review of Recent Developments
• Phenomenology of Low Quantum Gravity Scale Models
• The strong coupling, unification, and recent data
• Gauge Unification in Supersymmetric Intersecting Brane Worlds
• String GUTs
• Gauge Coupling Unification in Realistic Free-Fermionic String Models
• Natural gauge-coupling unification at the string scale
• Three Generations in the Fermionic Construction
• Stable Superstring Relics
• Making Ends Meet: String Unification and Low-Energy Data
• Testable Flipped SU(5) x U(1)_X Models
• String Unification, Higher-Level Gauge Symmetries, and Exotic Hypercharge Normalizations
• Realizing Higher-Level Gauge Symmetries in String Theory: New Embeddings for String GUTs
• Running of Soft Parameters in Extra Space-Time Dimensions
• The problems of unification-mismatch and low ${\alpha }_3$: A solution with light vector-like matter
• Some Three Generation (0,2) Calabi-Yau Models
• Spectra in Standard-like Z_3 Orbifold Models
• Raising the unification scale in supersymmetry
• How to Reach the Correct sin^2θ_W and α_S in String Theory
• Calculating Fermion masses in Superstring Derived Standard-like Models
• Universal moduli-dependent thresholds in Z(2)xZ(2) orbifolds
• Some Implications of Charge and Color Breaking in the MSSM
• String Scale Gauge Coupling Unification with Vector-like Exotics and Non-Canonical U(1)_Y Normalization
• Minimal String Unification and Constraint on Hidden Sector
• Extra $Z^{\prime }$s and $W^{\prime }$s in Heterotic--String Derived Models
• Grand Unification with Three Generations in Free Fermionic String Models
• Reconciling Grand Unification with Strings by Anisotropic Compactifications
• Gauge Coupling Unification due to Non-universal Soft Supersymmetry Breaking
• Gauge Coupling Unification in the Standard Model
• Gauge Coupling Unification in GUT and String Models
• Threshold corrections in orbifold models and superstring unification of gauge interactions
• String Gauge Unification and Infra-red Fixed Points in MSSM+X Models
• String Unification, Spaghetti Diagrams and Infra-Red Fixed Points
• GUTs and String-GUTs
• Light adjoint scalars and unification at the string scale
• Yukawa Unification in Heterotic String Theory
• Non SUSY and SUSY one--step Unification
• Higgs-portal dark matter from non-supersymmetric strings
• Unification Bounds on the Possible N=2 Supersymmetry Breaking Scale
• Stringy Unification Helps See-Saw Mechanism
• An [SU(3)]^4 Supersymmetric grand unified model