arXiv subjects

Patipan Uttayarat

Publications and source records attributed to Patipan Uttayarat.

26 records · Page 2Linked to original sources

arXiv2012

Massive Spin-2 States as the Origin of the Top Quark Forward-Backward Asymmetry

We show that the anomalously large top quark forward-backward asymmetry observed by CDF and DØ\, can naturally be accommodated in models with flavor-violating couplings of a new massive spin-2 state to quarks. Regardless of its origin, the lowest-order couplings of a spin-2 boson to fermions are analogous to the coupling of the graviton to energy/momentum, leading to strong sensitivity of the effects associated with its virtual exchange to the energy scales at hand. Precisely due to this fact, the observed dependence of the asymmetry on the $t\bar t$ invariant mass fits nicely into the proposed framework. In particular, we find a vast parameter space which can lead to the central value for the observed forward-backward asymmetry in the high mass bin, while being in accord with all of the existing experimental constraints.

hep-ph↗

arXiv2012

CP Violation and Flavor SU(3) Breaking in D-meson Decays

We carry out a systematic flavor SU(3) analysis of D-meson decays including the leading order symmetry breaking effects. We find that SU(3) breaking can easily account for the recent LHCb measurement of the difference in CP asymmetries in the decays of $D^0$ into $K^+K^-$ and $π^+π^-$ mesons, once an enhancement mechanism, similar to the $Δ=1/2$ rule in neutral kaon decays is assumed. As a byproduct of the analysis, one can make predictions regarding the individual asymmetries in $K^+K^-$, $π^+π^-$, as well as the $D^0 \to π^0π^0$ decay channels. Moreover, we find that the asymmetry in the decay $D^+\to π^+π^0$ vanishes in the leading approximation.

hep-ph↗

arXiv2012

Explaining the ttbar Forward-Backward Asymmetry from a GUT-Inspired Model

We consider a model that includes light colored scalars from the {\bf 45} and {\bf 50} representations of SU(5) in order to explain the CDF- and D$Ø$-reported $t\bar{t}$ forward-backward asymmetry, $A^{t\bar{t}}_{FB}$. These light scalars are, labeled by their charges under the Standard Model gauge groups, the $(6,1)_{4/3}$ and $(\bar{6},3)_{1/3}$ from the {\bf 50} and the $(8,2)_{1/2}$ from the {\bf 45}. When the Yukawa coupling of the {\bf 50} is reasonably chosen and that of the {\bf 45} kept negligible at the scale of $M_Z$, the model yields phenomenologically viable results in agreement with the total $A^{t\bar{t}}_{FB}$ reported by CDF at the 0.7$σ$ level and with $A^{t\bar{t}}_{FB} (M_{t\bar{t}} \ge 450 \text{GeV})$ at the 2.2$σ$ level. Additionally, the Yukawa coupling of the {\bf 50} remains perturbative to the GUT scale (which defines a "reasonably chosen" value at $M_Z$), and the presence of the light scalar from the {\bf 45} allows for gauge coupling unification at a scale of $M_{GUT} \sim 10^{17}$ GeV.

hep-ph↗

arXiv2011

A Very Light Dilaton

We present a completely perturbative model that displays behavior similar to that of walking technicolor. In one phase of the model RG-trajectories run towards an IR-fixed point but approximate scale invariance is spontaneously broken before reaching the fixed point. The trajectories then run away from it and a light dilaton appears in the spectrum. The mass of the dilaton is controlled by the "distance" of the theory to the critical surface, and can be adjusted to be arbitrarily small without turning off the interactions. There is a second phase with no spontaneous symmetry breaking and hence no dilaton, and in which RG trajectories do terminate at the IR-fixed point.

hep-ph↗

arXiv2011

Spontaneous CP Violation and Light Particles in The Littlest Higgs

Little Higgs models often feature spontaneously broken extra global symmetries, which must also be explicitly broken in order to avoid massless Goldstone modes in the spectrum. We show that a possible conflict with collective symmetry breaking then implies light modes coupled to the Higgs boson, leading to interesting phenomenology. Moreover, spontaneous CP violation is quite generic in such cases, as the explicit breaking may be used to stabilize physical CP odd phases in the vacuum. We demonstrate this in an SU(2) \times SU(2) \times U(1) variant of the Littlest Higgs, as well as in an original SU(6)/SO(6) model. We show that even a very small explicit breaking may lead to large phases, resulting in new sources of CP violation in this class of models.

hep-ph↗

arXiv2011

Hidden Fine Tuning In The Quark Sector Of Little Higgs Models

In Little Higgs models a collective symmetry prevents the higgs from acquiring a quadratically divergent mass at one loop. We have previously shown that the couplings in the Littlest Higgs model introduced to give the top quark a mass do not naturally respect the collective symmetry. We extend our previous work showing that the problem is generic: it arises from the fact that the would be collective symmetry of any one top quark mass term is broken by gauge interactions.

hep-ph↗

arXiv2010

One Loop Renormalization of the Littlest Higgs Model

In Little Higgs models a collective symmetry prevents the Higgs from acquiring a quadratically divergent mass at one loop. This collective symmetry is broken by weakly gauged interactions. Terms, like Yukawa couplings, that display collective symmetry in the bare Lagrangian are generically renormalized into a sum of terms that do not respect the collective symmetry except possibly at one renormalization point where the couplings are related so that the symmetry is restored. We study here the one loop renormalization of a prototypical example, the Littlest Higgs Model. Some features of the renormalization of this model are novel, unfamiliar form similar chiral Lagrangian studies.

hep-ph↗

arXiv2009

Hidden fine tuning in the quark sector of little higgs models

In little higgs models a collective symmetry prevents the higgs from acquiring a quadratically divergent mass at one loop. By considering first the littlest higgs model we show that this requires a fine tuning: the couplings in the model introduced to give the top quark a mass do not naturally respect the collective symmetry. We show the problem is generic: it arises from the fact that the would be collective symmetry of any one top quark mass term is broken by gauge interactions.

hep-ph↗