Oleg Antipin

Minimal Coleman-Weinberg theory explains the diphoton excess

We replace the standard Higgs-mechanism by the Coleman-Weinberg mechanism, and investigate its viability through the addition of a new scalar field. As we showed in a previous study, minimal models of this type can alleviate the hierarchy problem of the Higgs-mass through the so-called Veltman conditions. We here extend the previous analysis by taking into account the important difference between running mass and pole mass of the scalar states. We then investigate whether these theories can account for the 750 GeV excess in diphotons observed by the LHC collaborations. New QCD-colored fermions in the TeV mass range coupled to the new scalar state are needed to describe the excess. We further show, by explicit computation of the running of the couplings, that the model is under perturbative control till just above the masses of the heaviest states of the theory. We further suggest related testable signatures and thereby show that the LHC experiments can test these models.

Accidental composite dark matter

A bstractWe build models where Dark Matter candidates arise as composite states of a new confining gauge force, stable thanks to accidental symmetries. Restricting to renormalizable theories compatible with SU(5) unification, we find 13 models based on SU(N) gauge theories and 9 based on SO(N). We also describe other models that require non-renormalizable interactions. The two gauge groups lead to distinctive phenomenologies: SU(N) theories give complex DM, with potentially observable electric and magnetic dipole moments that lead to peculiar spin-independent cross sections; SO(N) theories give real DM, with challenging spin-dependent cross sections or inelastic scatterings. Models with Yukawa couplings also give rise to spin-independent direct detection mediated by the Higgs boson and to electric dipole moments for the electron. In some models DM has higher spin. Each model predicts a specific set of lighter composite scalars, possibly observable at colliders.

Search for RS gravitons via WLWL decays

Abstract The original Randall–Sundrum (RS) model with a warped extra dimension along with extensions provides the possibility for a simultaneous solution to Planck-weak hierarchy problem as well as the flavor puzzle in the Standard Model (SM). The most distinctive feature of this scenario is the existence of Kaluza–Klein (KK) gravitons whose masses and couplings to the SM fields are set by the TeV scale. In some realistic versions of this framework, the largest coupling of the gravitons to the observed particles is to the top quark and unphysical Higgses ( W L ± and Z L ) with the KK graviton (G) masses predicted to be ≳4 TeV. We extend earlier works on the KK graviton decays to the t t ¯ final state and to the “gold-plated” Z L Z L modes (with each Z decaying to e + e − or to μ + μ − ) by studying the resonant production of the gravitons and their subsequent decay to W L W L pair. We find that with 300 fb−1 integrated luminosity of data the semileptonic G → W ( → l ν l ) W ( → 2 jets ) mode offers a good opportunity to search for the RS KK graviton mode with mass lighter than ∼3–3.5 TeV at the CERN LHC. Efficient WW mass reconstruction in the semileptonic mode combined with an analysis of dilepton mass distribution in the purely leptonic channel, p p → W ( → l ν l ) W ( → l ′ ν l ′ ) may help to observe KK Z ′ and KK graviton separately. Suitably defined average energy of the charged lepton in the semileptonic mode may be used to distinguish decays from longitudinal versus transverse W-bosons.

Dynamical generation of the weak and Dark Matter scales from strong interactions

A bstractAssuming that mass scales arise in nature only via dimensional transmutation, we extend the dimension-less Standard Model by adding vector-like fermions charged under a new strong gauge interaction. Their non-perturbative dynamics generates a mass scale that is transmitted to the elementary Higgs boson by electro-weak gauge interactions. In its minimal version the model has the same number of parameters as the Standard Model, predicts that the electro-weak symmetry gets broken, predicts new-physics in the multi-TeV region and is compatible with all existing bounds, provides two Dark Matter candidates stable thanks to accidental symmetries: a composite scalar in the adjoint of SU(2)L and a composite singlet fermion; their thermal relic abundance is predicted to be comparable to the measured cosmological DM abundance. Some models of this type allow for extra Yukawa couplings; DM candidates remain even if explicit masses are added.

T-odd correlations from CP violating anomalous top-quark couplings revisited

We revisit the effect of CP violating anomalous top-quark couplings in tt production and decay. We consider tt production through gluon fusion (and light qq annihilation) followed by top-quark decay into bW or bl{nu}. We find explicit analytic expressions for all the triple products generated by the anomalous couplings that fully incorporate all spin correlations. Our results serve as a starting point for numerical simulations for the CERN LHC.

Standard model vacuum stability and Weyl consistency conditions

A bstractAt high energy the standard model possesses conformal symmetry at the classical level. This is reflected at the quantum level by relations between the different β functions of the model. These relations are known as the Weyl consistency conditions. We show that it is possible to satisfy them order by order in perturbation theory, provided that a suitable coupling constant counting scheme is used. As a direct phenomenological application, we study the stability of the standard model vacuum at high energies and compare with previous computations violating the Weyl consistency conditions.

The a theorem for Gauge-Yukawa theories beyond Banks-Zaks

We investigate the a theorem for nonsupersymmetric gauge-Yukawa theories beyond the leading order in perturbation theory. The exploration is first performed in a model-independent manner and then applied to a specific relevant example. Here, a rich fixed point structure appears including the presence of a merging phenomenon between non-trivial fixed points for which the a theorem has not been tested so far.

Conformal extensions of the standard model with Veltman conditions

Using the renormalization group framework we classify different extensions of the standard model according to their degree of naturality. A new relevant class of perturbative models involving elementary scalars is the one in which the theory simultaneously satisfies the Veltman conditions and is conformal at the classical level. We term these extensions perturbative natural conformal (PNC) theories. We show that PNC models are very constrained and thus highly predictive. Among the several PNC examples that we exhibit, we discover a remarkably simple PNC extension of the standard model in which the Higgs is predicted to have the experimental value of the mass equal to 126 GeV. This model also predicts the existence of one more standard model singlet scalar boson with a mass of 541 GeV and the Higgs self-coupling to emerge radiatively. We study several other PNC examples that generally predict a somewhat smaller mass of the Higgs to the perturbative order we have investigated them. Our results can be a useful guide when building extensions of the standard model featuring fundamental scalars.

Light dilaton at fixed points and ultra light scale super-Yang-Mills

Abstract We investigate the infrared dynamics of a nonsupersymmetric SU ( X ) gauge theory featuring an adjoint fermion, N f Dirac flavors and a Higgs-like complex N f × N f scalar which is a gauge singlet. We first establish the existence of an infrared stable perturbative fixed point and then investigate the spectrum near this point. We demonstrate that this theory features a light scalar degree of freedom to be identified with the dilaton and elucidate its physical properties. We compute the spectrum and demonstrate that at low energy the nonperturbative part of the spectrum of the theory is the one of pure supersymmetric Yang–Mills. We can therefore determine the exact nonperturbative fermion condensate and deduce relevant properties of the nonperturbative spectrum of the theory. We also show that the intrinsic scale of super-Yang–Mills is exponentially smaller than the scale associated to the breaking of conformal and chiral symmetry of the theory.

The Half-composite Two Higgs Doublet Model and the Relaxion

A bstractWe study a new confining gauge theory with fermions in a vectorial representation under the SM gauge group that allows for Yukawa interactions with the Higgs. If the fermion masses are smaller than the confinement scale this realizes a type I two Higgs doublet model where a composite Higgs mixes with the elementary Higgs. This class of models interpolates between an elementary and a composite Higgs and has interesting phenomenology with potentially observable effects in collider physics, EDMs and SM couplings but very weak bounds from indirect searches. The very same framework can be used to realize the cosmological relaxation of the electro-weak scale recently discussed in the literature.