arXiv subjects

Eric D'Hoker

Publications and source records attributed to Eric D'Hoker.

At least 127 records · Page 7Linked to original sources

arXiv1996

Gauge Symmetry Breaking through Soft Masses in Supersymmetric Gauge Theories

Effects of soft breaking in N=1 supersymmetric gauge theories are studied. For N_f < N_c, we include the dynamics of the non-perturbative superpotential and use the original (s)quark and gauge fields. For N_f > N_c +1, we formulate the dynamics in terms of dual (s)quarks and a dual gauge group SU(N_f-N_c). The mass squared of the squarks can be negative triggering spontaneous breakdown of flavor and color symmetry. The general condition for stability of the vacuum is derived. We determine the breaking pattern, determine the spectrum and argue that the masses vary smoothly as one crosses from the Higgs phase into the confining phase, thus exhibiting complementarity.

hep-ph↗

arXiv1996

The Renormalization Group Equation in N=2 Supersymmetric Gauge Theories

We clarify the mass dependence of the effective prepotential in N=2 supersymmetric SU(N_c) gauge theories with an arbitrary number N_f<2N_c of flavors. The resulting differential equation for the prepotential extends the equations obtained previously for SU(2) and for zero masses. It can be viewed as an exact renormalization group equation for the prepotential, with the beta function given by a modular form. We derive an explicit formula for this modular form when N_f=0, and verify the equation to 2-instanton order in the weak-coupling regime for arbitrary N_f and N_c.

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arXiv1996

High energy scattering of non-critical strings

We summarize recent work, in which we consider scattering amplitudes of non-critical strings in the limit where the energy of all external states is large compared to the string tension. We show that the high energy limit is dominated by a saddle point that can be mapped onto an electrostatic equilibrium configuration of an assembly of charges associated with the external states, together with a density of charges arising from the Liouville field. The Liouville charges accumulate on line segments, which produce quadratic branch cuts on the worldsheet. The electrostatics problem is solved for string tree level in terms of hyperelliptic integrals and is given explicitly for the 3- and 4-point functions. For generic values of the central charge, the high energy limit behaves in a string-like fashion, with exponential energy dependence.

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arXiv1996

The Effective Prepotential of N=2 Supersymmetric SO(N_c) and Sp(N_c) Gauge Theories

We calculate the effective prepotentials for N=2 supersymmetric SO(N_c) and Sp(N_c) gauge theories, with an arbitrary number of hypermultiplets in the defining representation, from restrictions of the prepotentials for suitable N=2 supersymmetric gauge theories with unitary gauge groups. (This extends previous work in which the prepotential for N=2 supersymmetric SU(N_c) gauge theories was evaluated from the exact solution constructed out of spectral curves.) The prepotentials have to all orders the logarithmic singularities of the one-loop perturbative corrections, as expected from non-renormalization theorems. We evaluate explicitly the contributions of one- and two-instanton processes.

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arXiv1996

Non-critical strings at high energy

We consider scattering amplitudes in non-critical string theory of $N$ external states in the limit where the energy of all external states is large compared to the string tension. We argue that the amplitudes are naturally complex analytic in the matter central charge $c$ and we propose to define the amplitudes for arbitrary value of $c$ by analytic continuation. We show that the high energy limit is dominated by a saddle point that can be mapped onto an equilibrium electro-static energy configuration of an assembly of $N$ pointlike (Minkowskian) charges, together with a density of charges arising from the Liouville field. We argue that the Liouville charges accumulate on segments of curves, and produce quadratic branch cuts on the worldsheet. The electro-statics problem is solved for string tree level in terms of hyper-elliptic integrals and is given explicitly for 3- and 4-point functions. We show that the high energy limit should behave in a string-like fashion with exponential dependence on the energy scale for generic values of $c$.

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arXiv1996

Gauge Symmetry Breaking through Soft Masses in Supersymmetric Gauge Theories

We analyze the effects of soft supersymmetry breaking terms on N=1 supersymmetric QCD with $N_f$ flavors and color gauge group $SU(N_c)$. The mass squared of some squarks may be negative, as long as vacuum stability is ensured by a simple mass inequality. For $N_f N_c+1$, we formulate the dynamics in terms of dual (s)quarks and a dual gauge group $SU(N_f-N_c)$. The presence of negative squark mass squared terms leads to spontaneous breakdown of flavor and color symmetry. We determine this breaking pattern, derive the spectrum, and argue that the masses vary smoothly as one crosses from the Higgs phase into the confining phase.

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arXiv1996

The Effective Prepotential of N=2 Supersymmetric SU(N_c) Gauge Theories

We determine the effective prepotential for N=2 supersymmetric SU(N_c) gauge theories with an arbitrary number of flavors N_f < 2N_c, from the exact solution constructed out of spectral curves. The prepotential is the same for the several models of spectral curves proposed in the literature. It has to all orders the logarithmic singularities of the one-loop perturbative corrections, thus confirming the non-renormalization theorems from supersymmetry. In particular, the renormalized order parameters and their duals have all the correct monodromy transformations prescribed at weak coupling. We evaluate explicitly the contributions of one- and two-instanton processes.

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arXiv1995

Worldline Path Integrals for Fermions with General Couplings

We derive a worldline path integral representation for the effective action of a multiplet of Dirac fermions coupled to the most general set of matrix-valued scalar, pseudoscalar, vector, axial vector and antisymmetric tensor background fields. By representing internal degrees of freedom in terms of worldline fermions as well, we obtain a formulation which manifestly exhibits chiral gauge invariance.

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arXiv1995

Worldline Path Integrals for Fermions with Scalar, Pseudoscalar and Vector Couplings

A systematic derivation is given of the worldline path integrals for the effective action of a multiplet of Dirac fermions interacting with general matrix-valued classical background scalar, pseudoscalar, and vector gauge fields. The first path integral involves worldline fermions with antiperiodic boundary conditions on the worldline loop and generates the real part of the one loop (Euclidean) effective action. The second path integral involves worldline fermions with periodic boundary conditions and generates the imaginary part of the (Euclidean) effective action, i.e. the phase of the fermion functional determinant. Here we also introduce a new regularization for the phase of functional determinants resembling a heat-kernel regularization. Compared to the known special cases, our worldline Lagrangians have a number of new interaction terms; the validity of some of these terms is checked in perturbation theory. In particular, we obtain the leading order contribution (in the heavy mass expansion) to the Wess-Zumino-Witten term, which generates the chiral anomaly.

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arXiv1995

General 2+1 Dimensional Effective Actions and Soliton Spin Fractionalization

We propose actions for non-linear sigma models on cosets $G/H$ in 2+1 dimensions that include the most general non-linear realizations of Chern-Simons terms. When $G$ is simply connected and $H$ contains $r$ commuting U(1) factors, there are $r$ different topologically conserved charges and generically $r$ different types of topological solitons. Soliton spin fractionalizes as a function of the Chern-Simons couplings, with independent spins associated to each species of soliton charge, as well as to pairs of different charges. This model of soliton spin fractionalization generalizes to arbitrary $G/H$ a model of Wilczek and Zee for one type of soliton.

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arXiv1995

Effective Energy for QED$_{2+1}$ with Semi-Localized Static Magnetic Fields: A Solvable Model

We evaluate the exact ${\rm QED}_{2+1}$ effective energy for charged spin zero and spin half fields in the presence of a family of static magnetic field profiles localized in a strip of width $λ$. The exact result yields an infinite set of relations between the terms in the derivative expansion of the effective energy for a general magnetic field. Upon addition of the standard Maxwell magneto-static energy, the minimum energy configuration at fixed flux corresponds to a uniform magnetic field.

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arXiv1995

Invariant Effective Actions and Cohomology

We review the correspondence between effective actions resulting from non-invariant Lagrangian densities, for Goldstone bosons arising from spontaneous breakdown of a symmetry group G to a subgroup H, and non-trivial generators of the de Rham cohomology of G/H. We summarize the construction of cohomology generators in terms of symmetric tensors with certain invariance and vanishing properties with respect to G and H. The resulting actions in four dimensions arise either from products of generators of lower degree such as the Goldstone-Wilczek current, or are of the Wess-Zumino-Witten type. Actions in three dimensions arise as Chern-Simons terms evaluated on composite gauge fields and may induce fractional spin on solitons. {Contribution to the Proceedings of STRINGS 95, held at University of Southern California, March 13 - 18, 1995.}

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arXiv1995

Invariant Effective Actions, Cohomology of Homogeneous Spaces and Anomalies

We construct the most general local effective actions for Goldstone boson fields associated with spontaneous symmetry breakdown from a group $G$ to a subgroup $H$. In a preceding paper, it was shown that any $G$-invariant term in the action, which results from a non-invariant Lagrangian density, corresponds to a non-trivial generator of the de Rham cohomology classes of $G/H$. Here, we present an explicit construction of all the generators of this cohomology for any coset space $G/H$ and compact, connected group $G$. Generators contributing to actions in 4-dimensional space-time arise either as products of generators of lower degree such as the Goldstone-Wilczek current, or are of the Wess-Zumino-Witten type. The latter arise if and only if $G$ has a non-zero $G$-invariant symmetric $d$-symbol, which vanishes when restricted to the subgroup $H$, i.e. when $G$ has anomalous representations in which $H$ is embedded in an anomaly free way. Coupling of additional gauge fields leads to actions whose gauge variation coincides with the chiral anomaly, which is carried here by Goldstone boson fields at tree level. Generators contributing to actions in 3-dimensional space-time arise as Chern-Simons terms evaluated on connections that are composites of the Goldstone field.

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arXiv1994

Casimir Forces between Beads on Strings and Membranes

We develop a general formalism to calculate the force between beads attached to a flat $d$-dimensional membrane due to the quantum fluctuations of the membrane. The interaction potential is derived as a function of $d$ and the membrane energy density, tension, stiffness and temperature. We find that the induced interactions turn off when $d$ exceeds a certain critical dimension. The potential is attractive in all cases where it is non-zero and at finite temperature falls off exponentially for large distances.

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arXiv1994

General Effective Actions

We investigate the structure of the most general actions with symmetry group $G$, spontaneously broken down to a subgroup $H$. We show that the only possible terms in the Lagrangian density that, although not $G$-invariant, yield $G$-invariant terms in the action, are in one to one correspondence with the generators of the fifth cohomology classes. For the special case of $G=SU(N)_L \times SU(N)_R$ broken down to the diagonal subgroup $H=SU(N)_V$, there is just one such term for $N\geq 3$, which for $N=3$ is the original Wess-Zumino-Witten term.

hep-ph↗

arXiv1994

Derivative Expansion of the Effective Action and Vacuum Instability for QED in 2+1 Dimensions

We investigate the effective action of 2+1 dimensional charged spin 1/2 fermions and spin 0 bosons in the presence of a $U(1)$ gauge field. We evaluate terms in an expansion up to second order in derivatives of the field strength, but exactly in the mass parameter and in the magnitude of the nonvanishing constant field strength. We find that in a strong uniform magnetic field background, space-derivative terms lower the energy, and there arises an instability toward inhomogeneous magnetic fields.

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arXiv1994

Dispersion Relations in String Theory

We analyze the analytic continuation of the formally divergent one-loop amplitude for scattering of the graviton multiplet in the Type II Superstring. In particular we obtain explicit double and single dispersion relations, formulas for all the successive branch cuts extending out to plus infinity, as well as for the decay rate of a massive string state of arbitrary mass 2N into two string states of lower mass. We compare our results with the box diagram in a superposition of $ϕ^3$-like field theories. The stringy effects are traced to a convergence problem in this superposition.

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arXiv1993

Geometrical origin of integrability for Liouville and Toda theory

We generalize the Lax pair and Bäcklund transformations for Liouville and Toda field theories as well as their supersymmetric generalizations, to the case of arbitrary Riemann surfaces. We make use of the fact that Toda field theory arises naturally and geometrically in a restriction of so called $W$--geometry to ordinary Riemannian geometry. This derivation sheds light on the geometrical structure underlying complete integrability of these systems. (Invited talk presented at the 877th meeting of the American Mathematical Society, USC, November 1992 and at the YITP workshop ``Directions on Quantum Gravity", Kyoto, November 1992.)

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