Supersymmetric QCD Research Articles

Neutralino-stop coannihilation into electroweak gauge and Higgs bosons at one loop

We compute the full O(alpha_s) supersymmetric QCD corrections for neutralino-stop co-annihilation into electroweak gauge and Higgs bosons in the Minimal Supersymmetric Standard Model (MSSM). We show that these annihilation channels are phenomenologically relevant within the so-called phenomenological MSSM, in particular in the light of the observation of a Higgs-like particle with a mass of about 126 GeV at the LHC. We present in detail our calculation, including the renormalization scheme, the infrared treatment, and the kinematical subtleties to be addressed. Numerical results for the co-annihilation cross sections and the predicted neutralino relic density are presented. We demonstrate that the impact of including the corrections on the cosmologically preferred region of parameter space is larger than the current experimental uncertainty from WMAP data.

New confinement phases from singular SCFT

New types of confining phase emerge when some singular SCFT's appearing as infrared fixed points of N=2 supersymmetric QCD (SQCD) are deformed by an N=1 adjoint mass term. We make further checks on the Gaiotto-Seiberg-Tachikawa (GST) description of these vacua against the symmetry and vacuum counting argument, and show that the GST variables correctly describe these systems, brought into confinement phase by the N=1 perturbation. Several examples of such vacua, USp(2N) and SU(N) theories with four flavors and SO(N) theories with one or two flavors, are discussed.

Physics of non-Abelian confinement and the dual gauge symmetry: Many faces of flavor symmetry

We review the physics of confinement based on non-Abelian dual superconductor picture, relying on exact solutions in N=2 supersymmetric QCD and based on the recent developments in our understanding of non-Abelian vortices and monopoles. The non-Abelian monopoles, though they are basically just the ʼt Hooft-Polyakov SU(2) monopoles embedded in various corners of the larger gauge group, require flavor symmetry in an essential way for their very existence. The phenomenon of flavor-color-flavor separation characterizes the multiple roles flavor symmetry plays in producing quantum-mechanical non-Abelian monopoles.

Photon structure functions with heavy particle mass effects

In the framework of the perturbative QCD we investigate heavy particle mass effects on the unpolarized and polarized photon structure functions, F2γ and g1γ, respectively. We present our basic formalism to treat heavy particle mass effects to NLO in perturbative QCD. We also study heavy quark effects on the QCD sum rule for the first moment of g1γ, which is related to axial anomaly. The photon structure function in supersymmetric QCD is also briefly discussed.

Singular SQCD vacua and confinement

We revisit the study of confining vacua in the softly broken $ \mathcal{N} $ = 2 supersymmetric QCD, in the light of some recent developments in our understanding of the dynamics of $ \mathcal{N} $ = 2 gauge theories. These vacua are characterized by an effective magnetic SU(r) gauge group (0 ≤ r ≤ N f /2) and are referred to sometimes as the r vacua. We further clarify the meaning of r ↔ N f − r duality arising from the matching of semi-classical and quantum vacua. A particular attention is paid to certain singular SCFT’s of $ \mathcal{N} $ = 2 SQCD, driven into confinement phase by the adjoint mass deformation μΦ2. In some cases they occur as a result of coalescence of different r vacua as the bare mass is tuned to a criticalvalue.

Exact kink solitons in a monopole confinement problem

We explicitly construct all kink solitons arising in the recent study of Auzzi, Bolognesi, and Shifman of a monopole confinement problem in ${\cal N}=2$ supersymmetric QCD. In particular, we show that all finite-energy kink solitons must be BPS.

Light Higgs scenario based on the TeV-scale supersymmetric strong dynamics

We consider a model based on the supersymmetric QCD theory with N_c=2 and N_f=3. The theory is strongly coupled at the infrared scale \Lambda_H. Its low energy effective theory below \Lambda_H is described by the supersymmetric standard model with the Higgs sector that contains four iso-spin doublets, two neutral iso-spin singlets and two charged iso-spin singlets. If \Lambda_H is at the multi-TeV to 10 TeV, coupling constants for the F-terms of these composite fields are relatively large at the electroweak scale. Nevertheless, the SM-like Higgs boson is predicted to be as light as 125 GeV because these F-terms contribute to the mass of the SM-like Higgs boson not at the tree level but at the one-loop level. A large non-decoupling effect due to these F-terms appears in the one-loop correction to the triple Higgs boson coupling, which amounts to a few tens percent. Such a non-decoupling property in the Higgs potential realizes the strong first order phase transition, which is required for a successful scenario of electroweak baryogenesis.

Supersymmetric next-to-next-to-leading order corrections to Higgs boson production in gluon fusion

We compute the total cross section for the production of a light CP even Higgs boson within the framework of supersymmetric QCD up to next-to-next-to-leading order. Technical subtleties in connection to the evaluation of three-loop Feynman integrals with many mass scales are discussed in detail and explicit results for the counterterms of the evanescent couplings are provided. The new results are applied to several phenomenological scenarios which are in accordance with the recent discovery at the LHC. In a large part of the still allowed parameter space the $K$ factor of the supersymmetric theory is close to the one of the Standard Model. However, for the case where one of the top squarks is light, a deviation of more than 5% in the next-to-next-to-leading order prediction of the cross section can be observed where at the same time the predicted Higgs boson mass has a value of about 125 GeV.

MSSM corrections to the top–antitop quark forward–backward asymmetry at the Tevatron

We study the effects of the complete supersymmetric QCD and electroweak one-loop corrections to the \(t\bar{t}\) forward–backward asymmetry at the Fermilab Tevatron \(p\bar{p}\) collider. We work in the complex Minimal Supersymmetric Standard Model (MSSM), only restricted by the condition of minimal flavor violation (MFV). We perform a comprehensive scan over the relevant parameter space of the complex MFV–MSSM and determine the maximal possible contributions of these MSSM loop corrections to the forward–backward asymmetry in the \(t\bar{t}\) center-of-mass frame. We find that the SUSY loop-induced asymmetry at the Tevatron with \(M_{t\bar{t}}>450~\mbox{GeV}\) can be at most +2 % for very light SUSY particles, i.e. for \(m_{\tilde{t}_{1}} <100~\mbox{GeV}\) and \(m_{\min} = \mathrm{Min}\{ m_{\tilde{g}},m_{\tilde{u}_{1,2}},m_{\tilde{d}_{1,2}}\}<100~\mbox{GeV}\), which reduces to 0.1 % for gluino and squark masses in the range 850 GeV–1000 GeV and a light top squark of \(m_{\tilde{t}_{1}}=200~\mbox{GeV}\).

RDuality and “instead-of-confinement” mechanism inN=1supersymmetric 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 \mu for the adjoint matter. We study r-vacua, with the constraint $2N_f/3 < r \le N. At large values of the parameter \xi\sim\mu m (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 \xi the 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 \mu thus 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 \mu. It determines low-energy non-Abelian dynamics in the r-vacua of N=1 SQCD.

Decoupling constant for α s and the effective gluon-Higgs coupling to three loops in supersymmetric QCD

We compute the three-loop QCD corrections to the decoupling constant for $\alpha_s$ which relates the Minimal Supersymmetric Standard Model to Quantum Chromodynamics with five or six active flavours. The new results can be used to study the stability of $\alpha_s$ evaluated at a high scale from the knowledge of its value at $M_Z$. We furthermore derive a low-energy theorem which allows the calculation of the coefficient function of the effective Higgs boson-gluon operator from the decoupling constant. This constitutes the first independent check of the matching coefficient to three loops.

Carving out the space of 4D CFTs

We introduce a new numerical algorithm based on semidefinite programming to efficiently compute bounds on operator dimensions, central charges, and OPE coefficients in 4D conformal and N=1 superconformal field theories. Using our algorithm, we dramatically improve previous bounds on a number of CFT quantities, particularly for theories with global symmetries. In the case of SO(4) or SU(2) symmetry, our bounds severely constrain models of conformal technicolor. In N=1 superconformal theories, we place strong bounds on dim(Phi*Phi), where Phi is a chiral operator. These bounds asymptote to the line dim(Phi*Phi) <= 2 dim(Phi) near dim(Phi) ~ 1, forbidding positive anomalous dimensions in this region. We also place novel upper and lower bounds on OPE coefficients of protected operators in the Phi x Phi OPE. Finally, we find examples of lower bounds on central charges and flavor current two-point functions that scale with the size of global symmetry representations. In the case of N=1 theories with an SU(N) flavor symmetry, our bounds on current two-point functions lie within an O(1) factor of the values realized in supersymmetric QCD in the conformal window.

The Hilbert series of [formula omitted][formula omitted] and [formula omitted] SQCD, Painlevé VI and integrable systems

We present a novel approach for computing the Hilbert series of 4d N=1 supersymmetric QCD with SO(Nc) and Sp(Nc) gauge groups. It is shown that such Hilbert series can be recast in terms of determinants of Hankel matrices. With the aid of results from random matrix theory, such Hankel determinants can be evaluated both exactly and asymptotically. Several new results on Hilbert series for general numbers of colours and flavours are thus obtained in this paper. We show that the Hilbert series give rise to families of rational solutions, with palindromic numerators, to the Painlevé VI equations. Due to the presence of such Painlevé equations, there exist integrable Hamiltonian systems that describe the moduli spaces of SO(Nc) and Sp(Nc) SQCD. To each system, we explicitly state the corresponding Hamiltonian and family of elliptic curves. It turns out that such elliptic curves take the same form as the Seiberg–Witten curves for 4d N=2SU(2) gauge theory with 4 flavours.

New results for the SQCD Hilbert series

We derive new explicit results for the Hilbert series of N=1 supersymmetric QCD with U(N_c) and SU(N_c) color symmetry. We use two methods which have previously been applied to similar computational problems in the analysis of decay of unstable D-branes: expansions using Schur polynomials, and the log-gas approach related to random matrix theory.

$ \mathcal{N} = 1 $ SQCD and the transverse field Ising model

We study the dimensions of non-chiral operators in the Veneziano limit of N=1 supersymmetric QCD in the conformal window. We show that when acting on gauge-invariant operators built out of scalars, the 1-loop dilatation operator is equivalent to the spin chain Hamiltonian of the 1D Ising model in a transverse magnetic field, which is a nontrivial integrable system that is exactly solvable at finite length. Solutions with periodic boundary conditions give the anomalous dimensions of flavor-singlet operators and solutions with fixed boundary conditions give the anomalous dimensions of operators whose ends contain open flavor indices.

Cosmological axino problem

We revisit the cosmology of the supersymmetric QCD axion, highlighting the existence of a serious cosmological axino problem that is fully analogous to the gravitino problem of overclosure via thermal production. A general analysis implies that the QCD axino has a mass greater than or equal to that of the gravitino in the absence of unnatural fine-tuning or sequestering. As a consequence, bounds from thermal gravitino and QCD axino production are complementary in parameter space, and together provide a quite stringent limit on the reheating temperature after inflation given by T_R < 10^3 - 10^6 GeV for an axion decay constant of f_a = 10^9 - 10^12 GeV. Motivated by this result, we explore the cosmology of gravitino LSP and axino NLSP at low T_R and present three realistic scenarios for dark matter.

Photon structure function in supersymmetric QCD revisited

We investigate the virtual photon structure function in the supersymmetric QCD (SQCD), where we have squarks and gluinos in addition to the quarks and gluons. Taking into account the heavy particle mass effects to the leading order in QCD and SQCD we evaluate the photon structure function and numerically study its behavior for the QCD and SQCD cases.

SUSY QCD corrections to electroweak gauge boson production with an associated jet at the LHC

We study the stability of the neutral- and charged-current Drell-Yan process in association with a jet as a standard candle at the LHC under the inclusion of O(alpha_s) supersymmetric QCD (SQCD) corrections within the MSSM. We include the decay of the electroweak gauge boson into dileptons, i.e. we consider the production of charged lepton--anti-lepton or lepton-neutrino final states with one hard jet. We find that the SQCD corrections are negligible for the integrated cross section. Only at high lepton transverse momentum can they induce effects of the percent level.

On O(N c) d = 3 $ \mathcal{N} = 2 $ supersymmetric QCD theories

We study three dimensional N=2 supersymmetric QCD theories with O(N_c) gauge groups and with N_f chiral multiplets in the vector representation. We argue that for N_f < N_c-2 there is a runaway potential on the moduli space and no vacuum. For N_f >= N_c-2 there is a moduli space also in the quantum theory, and for N_f >= N_c-1 there is a superconformal fixed point at the origin of this moduli space that has a dual description as the low-energy fixed point of an O(N_f-N_c+2) gauge theory. We test this duality in various ways; in some cases the duality for an O(2) gauge theory may be related to the known duality for U(1) gauge theories. We also discuss real mass deformations, which allow to connect theories with a different Chern-Simons level. This allows us to connect our duality with the known duality in O(N_c) theories with a Chern-Simons term of level k, where the dual gauge group is given by O(N_f+|k|-N_c+2).

Hidden local symmetry and color confinement

The hidden local symmetry is a successful model to describe the properties of the vector mesons in QCD. We point out that if we identify this hidden gauge theory as the magnetic picture of QCD, a linearized version of the model simultaneously describes color confinement and chiral symmetry breaking. We demonstrate that such a structure can be seen in the Seiberg dual picture of a softly broken supersymmetric QCD. The model possesses exact chiral symmetry and reduces to QCD when mass parameters are taken to be large. Working in the regime of the small mass parameters, we show that there is a vacuum where chiral symmetry is spontaneously broken and simultaneously the magnetic gauge group is Higgsed. If the vacuum we find persists in the limit of large mass parameters, one can identify the rho meson as the massive magnetic gauge boson, that is an essential ingredient for color confinement.