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M. Shifman

Publications and source records attributed to M. Shifman.

At least 55 records · Page 3Linked to original sources
arXiv2013

Revisiting the Faddeev-Skyrme Model and Hopf Solitons

We observe that the Faddeev-Skyrme model emerges as a low-energy limit of scalar QED with two charged scalar fields and a selfinteraction potential of a special form (inspired by supersymmetric QCD). Then we discuss possible Hopf solitons of the "twisted-toroidal" type.

hep-th↗
arXiv2013

Abrikosov-Nielsen-Olesen string with Non-Abelian Moduli and "Spin-Orbit" Interaction

It is generally believed that the spontaneous breaking of the Poincaré group by flux tubes (strings) generate only two zero modes localized on the string and associated with the spontaneous breaking of translational invariance (the so-called Low-Manohar argument). Being perfectly true in many instances it is nevertheless nonuniversal, and have to be amended in the case of order parameters carrying spatial indices. We show that under certain circumstances additional zero (or quasizero) modes can appear due to spin symmetry.

hep-th↗
arXiv2013

Detailing N=1 Seiberg's Duality through the Seiberg-Witten Solution of N=2

Starting from the Seiberg-Witten solution of N=2 SQCD with the U(N) gauge group and N_f quark flavors we construct the so-called μ-dual N=1 theory in the r vacua in the regime analogous to that existing to the left of the left edge of the Seiberg conformal window (here r is the number of condensed quarks). The strong-weak coupling duality is shown to exist in the so-called zero vacua which can be found at r< N_f-N. We show that the μ-dual theory matches the Seiberg dual in the zero vacua.

hep-th↗
arXiv2013

Hybrid r-Vacua in N=2 Supersymmetric QCD: Universal Condensate Formula

We derive an exact unified formula for all condensates (quark and monopole) in the hybrid r vacua in N=2 supersymmetric QCD slightly deformed by a μA^2 term. The gauge group is assumed to be U(N) and the number of the quark flavors N_f subject to the condition N< N_f < 2N. In the r vacua r quarks and N-r-1 monopoles from non-overlapping subgroups of U(N) develop vacuum expectation values (r<N). We then briefly review possible dynamical regimes (confinement, screening, and "instead of confinement") in the hybrid r vacua in μ-deformed N=2 SQCD (the small-μlimit).

hep-th↗
arXiv2013

Simple Models with Non-Abelian Moduli on Topological Defects

I explain how conventional topological defects -- the Abrikosov-Nielsen-Olesen (ANO) string and domain walls -- can acquire non-Abelian moduli localized on their world sheets. The set-up is conceptually similar and generalizes that used by Witten for cosmic strings.

hep-th↗
arXiv2012

A Remark on Supersymmetric Bubbles and Spectrum Crossover

Using an exact expression for the domain wall tension in a supersymmetric model we show that a spectrum crossover takes place in passing from weak to strong coupling. In the weak coupling regime elementary excitations are the lightest states, while in the strong coupling regime solitonic objects of a special type -- bubbles -- assume the role of the lightest states. The crossover occurs at λ^2/(4π) \sim 0.4.

hep-th↗
arXiv2012

How Chiral Symmetry Breaking Affects the Spectrum of the Light-Heavy Mesons in the 't Hooft Model

We find the spectrum and wave functions of the heavy-light mesons in $(1 + 1)$-dimensional QCD in the 't Hooft limit, both in the rest frame, using the Coulomb (axial) gauge, and on the light cone. Our emphasis is on the effects of chiral symmetry breaking on the spectrum. While dynamical equations in both cases look different, the results for the spectrum are identical. The chiral symmetry breaking is clearly seen from the gap and Bethe--Salpeter equations in the laboratory frame. At the same time, while vacuum is trivial on the light cone (no chiral condensate), the effects of the spontaneous breaking of the chiral symmetry manifest themselves in the same way, as it follows from the coincidence of the spectra obtained from the laboratory-frame Bethe--Salpeter equation on the one hand, and the light-cone 't Hooft-type equation on the other.

hep-th↗
arXiv2012

r Duality and "Instead-of-Confinement" Mechanism in N=1 Supersymmetric QCD

We consider N=2 SQCD with the U(N) gauge group and N_f flavors (N_f>N) perturbed by an N=2 breaking deformation - a small mass term μfor the adjoint matter. We study r-vacua, with the constraint $2N_f/3 < r \le N. At large values of the parameter ξ\simμm (m is a typical value of the quark masses) r quark flavors condense, by construction. The effective low-energy theory with the gauge group U(r)\times U(1)^{N-r} is at weak coupling. Upon reducing ξthe original theory undergoes a crossover transition from weak to strong coupling. As the original theory becomes strongly coupled, at low energies it is described by a weakly coupled infrared-free dual theory with the gauge group U(N_f-r)\times U(1)^{N-N_f+r} and N_f light dyon flavors. These dyons condense triggering formation of non-Abelian strings which still confine monopoles, rather than quarks, contrary to naive duality arguments. "Instead-of-confinement" mechanism for quarks and gauge bosons of the original theory takes place: screened quarks and gauge bosons of the original theory decay, on curves of the marginal stability (CMS), into confined monopole-antimonopole pairs that form stringy mesons. Next, we increase the deformation parameter μthus decoupling the adjoint fields. Then our theory flows to N=1 SQCD. The gauge group of the dual theory becomes U(N_f-r). We show that the dual theory is weakly coupled if we are sufficiently close to the Argyres-Douglas point. The "instead-of-confinement" mechanism for quarks and gauge bosons survives in the limit of large μ. It determines low-energy non-Abelian dynamics in the r-vacua of N=1 SQCD.

hep-th↗
arXiv2012

Confronting Seiberg's Duality with r Duality in N=1 Supersymmetric QCD

Systematizing our results on r duality obtained previously we focus on comparing r duality with the generalized Seiberg duality in the r vacua of N=2 and N=1 super-Yang-Mills theories with the U(N) gauge group and N_f matter flavors (N_f>N). The number of condensed (s)quarks r is assumed to be in the interval 2N_f/3 < r \le N. To pass to N=1 we introduce an N=2-breaking deformation, a mass term μfor the adjoint matter, eventually decoupling the adjoint matter in the limit of large μ. If one starts from a large value of the parameter ξ\simμm, where the original theory is at weak coupling, and decreases ξone hits a a crossover transition from weak to strong coupling (here m is a typical value of the quark masses). Below this transition the original theory is described in terms of a weakly coupled infrared-free r dual theory with the U(N_f-r) gauge group and N_f light quark-like dyon flavors. Dyon condensation leads to confinement of monopoles, defying a naive expectation of quark confinement. The quarks and gauge bosons of the original theory are in an "instead-of-confinement" phase. The r and Seiberg dualities are demonstrated to coincide in the r=N vacua. In the (2/3) N_f <r<N vacua two dualities do not match. In this window Seiberg's dual is at strong coupling while our r-dual model is at weak coupling. Thus, we can speak of triality. Seiberg's dual solution at weak coupling reappears again at r<N_f-N< (1/3) N_f$.

hep-th↗
arXiv2011

Higgs Decay into Two Photons through the W-boson Loop: No Decoupling in the m_W --> 0 Limit

We reanalyze the W-boson loop in the amplitude of the Higgs decay into two photons to show the absence of decoupling in the limit of massless W bosons, m_W --> 0. The Higgs coupling to longitudinal polarizations survive in this limit and generates a nonvanishing contribution in the $H\to γγ$ decay. This shows that the recent claim of decoupling by R. Gastmans, S.L. Wu, and T.T. Wu is incorrect, and the old calculations for the two photon decay well known in the literature are valid.

hep-ph↗
arXiv2011

N=(0,2) Supersymmetry and a Nonrenormalization Theorem

In this paper we continue the study of perturbative renormalizations in an $\mathcal{N}=(0,2)$ supersymmetric model. Previously we analyzed one-loop graphs in the heterotically deformed CP$(N-1)$ models. Now we extend the analysis of the $β$ function and appropriate $Z$ factors to two, and, in some instances, all loops in the limiting case $g^2\to 0$. The field contents of the model, as well as the heterotic coupling, remain the same, but the target space becomes flat. In this toy $\mathcal{N}=(0,2)$ model we construct supergraph formalism. We show, by explicit calculations up to two-loop order, that the $β$ function is one-loop-exact. We derive a nonrenormalization theorem valid to all orders. This nonrenormalization theorem is rather unusual since it refers to (formally) $D$ terms. It is based on the fact that supersymmetry combined with target space symmetries and "flavor"? symmetries is sufficient to guarantee the absence of loop corrections. We analyze the supercurrent supermultiplet (i.e., the hypercurrent) providing further evidence in favor of the absence of higher loops in the $β$ function.

hep-th↗
arXiv2011

Description of the Heterotic String Solutions in U(N) SQCD

We continue the study of heterotic non-Abelian BPS-saturated flux tubes (strings). Previously, such solutions were obtained [1] in a particular U(2) gauge theory: N=2 supersymmetric QCD deformed by superpotential terms of a special type breaking N=2 supersymmetry down to N=1. Here we generalize the previous results to U(N) gauge theories. As was suggested by Edalati and Tong [2], the string world sheet theory is a heterotic N=(0,2) sigma model, with the CP(N-1) target space for bosonic fields and an extra right-handed fermion which couples to the fermion fields of the N=(2,2) CP(N-1) model. We derive the heterotic N=(0,2) world sheet model directly from the U(N) bulk theory. Parameters of the bulk theory are related to those of the world sheet theory. Qualitatively this relation turns out to be the same as in the U(2) case.

hep-th↗
arXiv2011

Effective World-Sheet Theory for Non-Abelian Semilocal Strings in N = 2 Supersymmetric QCD

We consider non-Abelian semilocal strings (vortices, or vortex-strings) arising in N=2 supersymmetric U(N) gauge theory with Nf=N+Ñ matter hypermultiplets in the fundamental representation (quarks), and a Fayet-Iliopoulos term ξ. We present, for the first time ever, a systematic field-theoretic derivation of the world-sheet theory for such strings, describing dynamics of both, orientational and size zero modes. Our derivation is complete in the limit, ln(L)\rightarrow \infty, where L is an infrared (IR) regulator in the transverse plane. In this limit the world-sheet theory is obtained exactly. It is presented by a so far unknown N=2 two-dimensional sigma model, to which we refer as the zn model, with or without twisted masses. Alternative formulations of the zn model are worked out: conventional and extended gauged formulations and a geometric formulation. We compare the exact metric of the zn model with that of the weighted CP(Nf-1) model conjectured by Hanany and Tong, through D-branes, as the world-sheet theory for the non-Abelian semilocal strings. The Hanany-Tong set-up has no parallel for the field-theoretic IR parameter and metrics of the weighted CP(Nf-1) model and zn model are different. Still their quasiclassical excitation spectra coincide.

hep-th↗
arXiv2011

Non-Abelian Duality and Confinement: from N=2 to N=1 Supersymmetric QCD

Recently we discovered and discussed non-Abelian duality in the quark vacua of N=2 super-Yang-Mills theory with the U(N) gauge group and N_f flavors (N_f>N). Both theories from the dual pair support non-Abelian strings which confine monopoles. Now we introduce an N=2-breaking deformation, a mass term μ{\mathcal A}^2 for the adjoint fields. Starting from a small deformation we eventually make it large which enforces complete decoupling of the adjoint fields. We show that the above non-Abelian duality fully survives in the limit of N=1 SQCD, albeit some technicalities change. For instance, non-Abelian strings which used to be BPS-saturated in the N=2 limit, cease to be saturated in N=1 SQCD. Our duality is a distant relative of Seiberg's duality in N=1 SQCD. Both share some common features but have drastic distinctions. This is due to the fact that Seiberg's duality apply to the monopole rather than quark vacua. More specifically, in our theory we deal with N< N_f<3/2 N massive quark flavors. We consider the vacuum in which N squarks condense. Then we identify a crossover transition from weak to strong coupling. At strong coupling we find a dual theory, U(N_f-N) SQCD, with N_f light dyon flavors. Dyons condense triggering the formation of non-Abelian strings which confine monopoles. Screened quarks and gauge bosons of the original theory decay into confined monopole-antimonopole pairs and form stringy mesons.

hep-th↗