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F-Yang–Mills equations

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In differential geometry, the -Yang–Mills equations (or -YM equations) are a generalization of the Yang–Mills equations. Its solutions are called -Yang–Mills connections (or -YM connections). Simple important cases of -Yang–Mills connections include exponential Yang–Mills connections using the exponential function for and -Yang–Mills connections using as exponent of a potence of the norm of the curvature form similar to the -norm. Also often considered are Yang–Mills–Born–Infeld connections (or YMBI connections) with positive or negative sign in a function involving the square root. This makes the Yang–Mills–Born–Infeld equation similar to the minimal surface equation.

F-Yang–Mills action functional

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Let be a strictly increasing function (hence with ) and . Let:[1]

Since is a function, one can also consider the following constant:[2]

Let be a compact Lie group with Lie algebra and be a principal -bundle with an orientable Riemannian manifold having a metric and a volume form . Let be its adjoint bundle. is the space of connections, which are either under the adjoint representation invariant Lie algebra–valued or vector bundle–valued differential forms. Since the Hodge star operator is defined on the base manifold as it requires the metric and the volume form , the second space is usually used.

The -Yang–Mills action functional is given by:[2][3]

For a flat connection (with ), one has . Hence is required to avert divergence for a non-compact manifold , although this condition can also be left out as only the derivative is of further importance.

F-Yang–Mills connections and equations

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A connection is called -Yang–Mills connection, if it is a critical point of the -Yang–Mills action functional, hence if:

for every smooth family with . This is the case iff the -Yang–Mills equations are fulfilled:[2][3]

For a -Yang–Mills connection , its curvature is called -Yang–Mills field.

A -Yang–Mills connection/field with:[1][2][3]

  • is just an ordinary Yang–Mills connection/field.
  • (or for normalization) is called (normed) exponential Yang–Mills connection/field. In this case, one has . The exponential and normed exponential Yang–Mills action functional are denoted with and respectively.[4]
  • is called -Yang–Mills connection/field. In this case, one has . Usual Yang–Mills connections/fields are exactly the -Yang–Mills connections/fields. The -Yang–Mills action functional is denoted with .
  • or is called Yang–Mills–Born–Infeld connection/field (or YMBI connection/field) with negative or positive sign respectively. In these cases, one has and respectively. The Yang–Mills–Born–Infeld action functionals with negative and positive sign are denoted with and respectively. The Yang–Mills–Born–Infeld equations with positive sign are related to the minimal surface equation:

Stable F-Yang–Mills connection

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Analogous to (weakly) stable Yang–Mills connections, one can define (weakly) stable -Yang–Mills connections. A -Yang–Mills connection is called stable if:

for every smooth family with . It is called weakly stable if only holds. A -Yang–Mills connection, which is not weakly stable, is called unstable.[3] For a (weakly) stable or unstable -Yang–Mills connection , its curvature is furthermore called a (weakly) stable or unstable -Yang–Mills field.

Properties

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  • For a Yang–Mills connection with constant curvature, its stability as Yang–Mills connection implies its stability as exponential Yang–Mills connection.[4]
  • Every non-flat exponential Yang–Mills connection over with and:
is unstable.[2][3]
  • Every non-flat Yang–Mills–Born–Infeld connection with negative sign over with and:
is unstable.[2]
  • All non-flat -Yang–Mills connections over with are unstable.[2][3] This result includes the following special cases:
    • All non-flat Yang–Mills connections with positive sign over with are unstable.[5][6][7] James Simons presented this result without written publication during a symposium on "Minimal Submanifolds and Geodesics" in Tokyo in September 1977.
    • All non-flat -Yang–Mills connections over with are unstable.
    • All non-flat Yang–Mills–Born–Infeld connections with positive sign over with are unstable.
  • For , every non-flat -Yang–Mills connection over the Cayley plane is unstable.[3]

Literature

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  • Chiang, Yuan-Jen (2013-06-18). Developments of Harmonic Maps, Wave Maps and Yang-Mills Fields into Biharmonic Maps, Biwave Maps and Bi-Yang-Mills Fields. Frontiers in Mathematics. Birkhäuser. doi:10.1007/978-3-0348-0534-6. ISBN 978-3034805339.

See also

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References

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  1. ^ a b Wei, Shihshu Walter (2022-05-06). "On exponential Yang-Mills fields and p-Yang-Mills fields". arXiv:2205.03016 [math.DG].
  2. ^ a b c d e f g Baba, Kurando; Shintani, Kazuto (2023-01-11). "A Simons type condition for instability of F-Yang-Mills connections". arXiv:2301.04291 [math.DG].
  3. ^ a b c d e f g Baba, Kurando (2023-11-20). "On instability of F-Yang-Mills connections" (PDF). www.rs.tus.ac.jp. Retrieved 2024-11-02.
  4. ^ a b Matsura, Fumiaki; Urakawa, Hajime (September 1995). "On exponential Yang-Mills connections". Journal of Geometry and Physics. 17 (1): 73–89. doi:10.1016/0393-0440(94)00041-2.
  5. ^ Bourguignon, Jean-Pierre; Lawson, Jr., H. Blaine (March 1981). "Stability and Isolation Phenomena for Yang-Mills Fields". Communications in Mathematical Physics. 79 (2): 189–230. doi:10.1007/BF01942061.
  6. ^ Kobayashi, S.; Ohnita, Y.; Takeuchi, M. (1986). "On instability of Yang-Mills connections" (PDF). Mathematische Zeitschrift. 193 (2). Springer: 165–189. doi:10.1007/BF01174329.
  7. ^ Chiang 2013, Theorem 3.1.9
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