Breaking Terms Research Articles

B → τν in two-Higgs doublet models with MFV

We analyse the B → τν decay in a generic two-Higgs doublet model satisfying the MFV hypothesis. In particular, we analyse under which conditions $$\mathcal{B}(B \to \tau \nu )$$ can be substantially enhanced over its SM value, taking into account the constraints of K → τν, B → X s γ, and B s → μ + μ −. We find that for large tan β values and Peccei-Quinn symmetry breaking terms of $$\mathcal{O}(1/\tan \beta )$$ a sizable (∼ 50%) enhancement of $$\mathcal{B}(B \to \tau \nu )$$ is possible, even for m H ∼ 1 TeV.

Near-BPS Skyrmions: Nonshell configurations and Coulomb effects

The relatively small binding energy in nuclei suggests that they may be well represented by near-BPS Skyrmions since their mass is roughly proportional to the baryon number $A.$ For that purpose, we propose a generalization of the Skyrme model with terms up to order six in derivatives of the pion fields and treat the nonlinear $\sigma$ and Skyrme terms as small perturbations. For our special choice of mass term (or potential) $V$, we obtain well-behaved analytical BPS-type solutions with non-shell configurations for the baryon density, as opposed to the more complex shell-like configurations found in most extensions of the Skyrme model . Along with static and (iso)rotational energies, we add to the mass of the nuclei the often neglected Coulomb energy and isospin breaking term. Fitting the four model parameters, we find a remarkable agreement for the binding energy per nucleon $B/A$ with respect to experimental data. These results support the idea that nuclei could be near-BPS Skyrmions.

The messenger sector of SUSY flavour models and radiative breaking of flavour universality

Abstract The flavour messenger sectors and their impact on the soft SUSY breaking terms are investigated in SUSY flavour models. In the case when the flavour scale M is below the SUSY breaking mediation scale M S , the universality of soft terms, even if assumed at M S , is radiatively broken. We estimate this effect in a broad class of models. In the CKM basis that effect gives flavour off-diagonal soft masses comparable to the tree-level estimate based on the flavour symmetry.

Gauge theory andSIM(2)superspace

In this paper the SIM(2) superspace formulation of the supersymmetric Yang-Mills gauge theory minimally coupled to chiral superfields is discussed. The super-Poincare invariant supersymmetric Yang-Mills theory is rewritten to SIM(2) superspace formalism and the effects of SIM(2) invariant but Lorentz breaking terms are discussed. Two approaches are investigated. The first is based on the gauge chiral representation of the supersymmetric gauge theory and the second is based on the covariant representation of the supersymmetric gauge theory.

Neutralino dark matter in mSUGRA/CMSSM with a 125 GeV light Higgs scalar

The minimal supergravity (mSUGRA or CMSSM) model is an oft-used frame- work for exhibiting the properties of neutralino (WIMP) cold dark matter (CDM). How- ever, the recent evidence from Atlas and CMS on a light Higgs scalar with mass $ {m_h} \simeq 125 $ GeV highly constrains the superparticle mass spectrum, which in turn constrains the neutralino annihilation mechanisms in the early universe. We find that stau and stop co-annihilation mechanisms — already highly stressed by the latest Atlas/CMS re- sults on SUSY searches — are nearly eliminated if indeed the light Higgs scalar has mass $ {m_h} \simeq 125 $ GeV. Furthermore, neutralino annihilation via the A-resonance is nearly ruled out in mSUGRA so that it is exceedingly difficult to generate thermally-produced neutralino-only dark matter at the measured abundance. The remaining possibility lies in the focus-point region which now moves out to $ {m_0} \sim 10 - 20 $ TeV range due to the required large trilinear soft SUSY breaking term A0. The remaining HB/FP region is more fine-tuned than before owing to the typically large top squark masses. We present updated direct and indirect detection rates for neutralino dark matter, and show that ton scale noble liquid detectors will either discover mixed higgsino CDM or essentially rule out thermally-produced neutralino-only CDM in the mSUGRA model.

The heterotic string yields natural supersymmetry

The most promising MSSM candidates of the heterotic string reveal some distinctive properties. These include gauge-top unification, a specific solution to the μ-problem and mirage pattern for the gaugino masses. The location of the top- and the Higgs-multiplets in extra dimensions differs significantly from that of the other quarks and leptons leading to a characteristic signature of suppressed soft breaking terms, reminiscent of a scheme known as natural supersymmetry.

Supersymmetry, chiral symmetry and the generalized BRS transformation in lattice formulations of 4D [formula omitted] SYM

In the context of the lattice regularization of the four-dimensional N=1 supersymmetric Yang–Mills theory (4D N=1 SYM), we formulate a generalized BRS transformation that treats the gauge, supersymmetry (SUSY), translation and axial U(1) (U(1)A) transformations in a unified way. A resultant Slavnov–Taylor identity or the Zinn-Justin equation gives rise to a strong constraint on the quantum continuum limit of symmetry breaking terms with the lattice regularization. By analyzing the implications of the constraint on operator-mixing coefficients in the SUSY and the U(1)A Ward–Takahashi (WT) identities, we prove to all orders of perturbation theory in the continuum limit that, (i) the chiral symmetric limit implies the supersymmetric limit and, (ii) a three-fermion operator that might potentially give rise to an exotic breaking of the SUSY WT identity does not emerge. In previous literature, only a naive or incomplete treatment on these points can be found. Our results provide a solid theoretical basis for lattice formulations of the 4D N=1 SYM.

Symmetry breaking and restoration for interacting scalar and gauge fields in Lifshitz type theories

We consider the one-loop effective potential at zero and finite temperature in field theories with anisotropic space–time scaling, with critical exponent z=2, including both scalar and gauge fields. Depending on the relative strength of the coupling constants for the gauge and scalar interactions, we find that there is a symmetry breaking term induced at one loop at zero temperature and we find symmetry restoration through a first-order phase transition at high temperature.

New perturbation theory representation of the conformal symmetry breaking effects in gauge quantum field theory models

We propose a hypothesis on the detailed structure for the representation of the conformal symmetry breaking term in the basic Crewther relation generalized in the perturbation theory framework in QCD renormalized in the ${\rm \bar{MS}}$ scheme. We establish the validity of this representation in the $O(\alpha_s^4)$ approximation. Using the variant of the generalized Crewther relation formulated here allows finding relations between specific contributions to the QCD perturbation series coefficients for the flavor nonsinglet part of the Adler function $D^{ns}_A$ for the electron-positron annihilation in hadrons and to the perturbation series coefficients for the Bjorken sum rule $S_\text{Bjp}$ for the polarized deep-inelastic lepton-nucleon scattering. We find new relations between the $\alpha_s^4$ coefficients of $D^{ns}_A$ and $S_\text{Bjp}$. Satisfaction of one of them serves as an additional theoretical verification of the recent computer analytic calculations of the terms of order $\alpha_s^4$ in the expressions for these two quantities.

Observing signals of the bulk matter Randall-Sundrum model through rare decays of supersymmetric particles

The bulk matter Randall-Sundrum (RS) model is a setup where standard model (SM) matter and gauge fields reside in the bulk of 5D warped spacetime while the Higgs field is confined on the IR brane. The wave functions of the 1st and 2nd generation matter particles are localized toward the UV brane and those of the 3rd generation toward the IR brane, so that the hierarchical structure of the Yukawa couplings arises geometrically without hierarchy in fundamental parameters. This paper discusses observing signals of this model in the case where the Kaluza-Klein scale is far above the collider scale, but the model is combined with the 5D minimal supersymmetric standard model (MSSM) and supersymmetric (SUSY) particles are in the reach of collider experiments. A general SUSY breaking mass spectrum consistent with the bulk matter RS model is considered: a SUSY breaking sector locates on the IR brane and its effects are mediated to 5D MSSM through a hybrid of gravity mediation, gaugino mediation, and gauge mediation. This paper argues that it is possible to observe the signals of the bulk matter RS model through rare decays of ``almost SU(2) singlet mass eigenstates'' that are induced by flavor-violating gravity mediation contributions to matter soft SUSY breaking terms.

QED with minimal and nonminimal couplings: on the quantum generation of Lorentz-violating terms in the pure photon sector

We consider an effective model formed by usual QED (minimal coupling) with the addition of a nonminimal Lorentz-violating interaction (proportional to a fixed 4-vector bμ) which may radiatively generate both CPT even and odd terms in the pure gauge sector. We show that gauge invariance from usual QED, considered as a limit of the model for bμ → 0, plays an important role in the discussion of the radiatively induced Lorentz-violating terms at one-loop order. Moreover, despite the nonrenormalizability of the (effective) model preventing us from readily extending our discussion to higher orders, it is still possible to display the general form of the breaking terms of the photon sector in the on-shell limit organized in powers of bμ which in turn can be considered as a small expansion parameter.

A unified approach to supersymmetry breaking

General formulae for the soft SUSY breaking terms, valid in any SUGRA context, were derived in the mid-nineties. Since SUSY is not expected to have quantum anomalies, they should be valid in the quantum theory and be RG invariant down to the soft SUSY breaking scale. This observation enables us to give a uniform treatment of all phenomenological models for SUSY breaking and transmission, such as AMSB, GMSB, etc. In particular we find that the much discussed RG invariant formulae for soft SUSY breaking parameters in AMSB, effectively depend on a strong assumption of factorizability of the matter Kaehler metric. We then argue that there is no necessity for having ad hoc constructions such as mAMSB to counteract the negative squared slepton mass problem, since the natural framework that emerges in a sequestered model is one in which gaugino masses are as in AMSB, and the other soft terms are generated by RG running as in gaugino mediation.

Symmetry breaking and restoration in Lifshitz type theories

We consider the one-loop effective potential at zero and finite temperature in scalar field theories with anisotropic space–time scaling. For z=2, there is a symmetry breaking term induced at one loop at zero temperature and we find symmetry restoration through a first-order phase transition at high temperature. For z=3, we considered at first the case with a positive mass term at tree level and found no symmetry breaking effects induced at one loop, and then we study the case with a negative mass term at tree level where we cannot conclude about symmetry restoration effects at high temperature because of the imaginary parts that appear in the effective potential for small values of the scalar field.

Anomalous U(1) mediation in large volume compactification

We study the general effects of anomalous U(1)_A gauge symmetry on soft supersymmetry (SUSY) breaking terms in large volume scenario, where the MSSM sector is localized on a small cycle whose volume is stabilized by the D-term potential of the U(1)_A. Since it obtains SUSY breaking mass regardless of the detailed form of K\"ahler potential, the U(1)_A vector superfield acts as a messenger mediating the SUSY breaking in the moduli sector to the MSSM sector. Then, through the loops of U(1)_A vector superfield, there arise soft masses of the order of m_{3/2}^2/8\pi^2 for scalar mass squares, m_{3/2}/(8\pi^2)^2 for gaugino masses, and m_{3/2}/8\pi^2 for A-paramteres. In addition, the massive U(1)_A vector superfield can have non-zero F and D-components through the moduli mixing in the K\"ahler potential, and this can result in larger soft masses depending upon the details of the moduli mixing. For instance, in the presence of one-loop induced moduli mixing between the visible sector modulus and the large volume modulus, the U(1)_A D-term provides soft scalar mass squares of the order of m_{3/2}^2. However, if the visible sector modulus is mixed only with small cycle moduli, its effect on soft terms depends on how to stabilize the small cycle moduli.

Higgs Bosons Near 125 GeV in the NMSSM with Constraints at the GUT Scale

We study the NMSSM with universal Susy breaking terms (besides the Higgs sector) at the GUT scale. Within this constrained parameter space, it is not difficult to find a Higgs boson with a mass of about 125 GeV and an enhanced cross-section in the diphoton channel. An additional lighter Higgs boson with reduced couplings and a mass≲123 GeV is potentially observable at the LHC. The NMSSM-specific Yukawa couplingsλandκare relatively large and tanβis small, such thatλ,κ, and the top Yukawa coupling are of𝒪(1)at the GUT scale. The lightest stop can be as light as 105 GeV, and the fine-tuning is modest. WMAP constraints can be satisfied by a dominantly Higgsino-like LSP with substantial bino, wino, and singlino admixtures and a mass of~60–90 GeV, which would potentially be detectable by XENON100.

Solutions for f(R) gravity coupled with electromagnetic field

In the presence of external, linear / nonlinear electromagnetic fields we integrate f(R) \sim R+2{\alpha}\surd(R+const.) gravity equations. In contrast to their Einsteinian cousins the obtained black holes are non-asymptotically flat with a deficit angle. In proper limits we obtain from our general solution the global monopole solution in f(R) gravity. The scale symmetry breaking term adopted as the nonlinear electromagnetic source adjusts the sign of the mass of the resulting black hole to be physical.

Supersymmetric aether

It has been suggested by Groot Nibbelink and Pospelov that Lorentz invariance can be an emergent symmetry of low-energy physics provided the theory enjoys a non-relativistic version of supersymmetry. We construct a model that realizes the latter symmetry dynamically: it breaks Lorentz invariance but leaves the supersymmetry generators intact. The model is a supersymmetric extension of the dynamical aether theory of Jacobson and Mattingly. It shows rich dynamics and possesses a family of inequivalent vacua realizing different symmetry breaking patterns. In particular, we find stable vacua that break spontaneously spatial isotropy. Supersymmetry breaking terms give masses to fermionic and bosonic partners of the aether field. We comment on the coupling of the model to supergravity and on the implications for Horava gravity.

Dynamics of Photogenerated Polaron-Excitons in Organic Semiconductors

In this work we performed numerical simulations of one π-conjugated polymer chain subjected to photogeneration. Within the SSH model modified to include the Brazoviskii-Kirova symmetry breaking term, we investigate the dynamics of photoexcitations to address the generation mechanism of polaron-excitons using the unrestricted Hartree-Fock approximation. It was obtained that after the photoexcitation the system relaxes spontaneously into a polaron-exciton in a transient state in a range of 200 fs. Our results also show that charged polarons are generated directly after this transient state.

Hard and soft supersymmetry breaking for ‘graphinos’ in uniform magnetic fields

Using irreducible and reducible representations of the Dirac matrices, we study the two- and four-component quantum mechanical supersymmetric (SUSY) theories for ultrarelativistic fermions in (2 + 1) dimensions (‘graphinos’) in a background uniform magnetic field perpendicular to their plane of motion. We then consider ordinary and parity-violating mass terms and identify the former as a soft SUSY breaking term and the latter as the hard SUSY breaking one.

Topological insulators from complex orbital order in transition-metal oxides heterostructures

Topological band insulators which are dynamically generated by electron-electron interactions have been theoretically proposed in two- and three-dimensional lattice models. We present evidence that the two-dimensional version can be stabilized in digital (111) heterostructures of transition-metal oxides as a result of purely local interactions. The topological phases are accompanied by spontaneous ordering of complex orbitals and we discuss their stability with respect to the Hund's rule coupling, Jahn-Teller interaction, and inversion-symmetry breaking terms. As main competitors we identify spin-nematic and magnetic phases.