arXiv subjects

Zhi-Wei Wang

Publications and source records attributed to Zhi-Wei Wang.

At least 73 records · Page 4Linked to original sources

arXiv2020

Transformation of scalar couplings between Coleman-Weinberg and MS schemes

The Coleman-Weinberg (CW) renormalization scheme for renormalization-group improvement of the effective potential is particularly valuable for CW symmetry-breaking mechanisms (including the challenging case of models with multiple scalar fields). CW mechanism is typically studied using models with classical scale invariance which not only provide a possibility for an alternative symmetry breaking mechanism but also partially address the gauge hierarchies through dimensional transmutation. As outlined in our discussion section, when the couplings are not large, models with CW symmetry-breaking mechanisms have also been shown to naturally provide the strong first-order phase transition necessary for stochastic gravitational wave signals. A full understanding of the CW-MS scheme transformation of couplings thus becomes important in the era of gravitational wave detection and precision coupling measurements. A generalized Coleman-Weinberg (GCW) renormalization scheme is formulated and methods for transforming scalar self-couplings between the GCW and MS (minimal-subtraction) renormalization schemes are developed. Scalar $λΦ^4$ theory with global $O(4)$ symmetry is explicitly studied up to six-loop order to explore the magnitude of this scheme transformation effect on the couplings. The dynamical rescaling of renormalization scales between the GCW and MS schemes can lead to significant (order of 10\%) differences in the coupling at any order, and consequently GCW-MS scheme transformation effects must be considered within precision determinations of scalar couplings in extensions of the Standard Model.

hep-ph↗

arXiv2020

Charging the Walking U(N)$\times$U(N) Higgs Theory as a Complex CFT

We apply a semi-classical method to compute the conformal field theory (CFT) data for the U(N)xU(N) non-abelian Higgs theory in four minus epsilon dimensions at its complex fixed point. The theory features more than one coupling and walking dynamics. Given our charge configuration, we identify a family of corresponding operators and compute their scaling dimensions which remarkably agree with available results from conventional perturbation theory validating the use of the state-operator correspondence for a complex CFT.

hep-th↗

arXiv2020

Gravitational Waves from Pati-Salam Dynamics

We show that it is possible to use gravitational wave detectors to observe the occurrence of a first order phase transition in Pati-Salam extensions of the Standard Model. We show that the peak frequency of the expected gravitational wave signals ranges within $0.1-10$ Hz. We find amusing that the next generation of gravity waves detectors are able to explore time honoured extensions of the Standard Model occurring at energy scales inaccessible by present and future particle physics accelerators.

hep-ph↗

arXiv2019

Direct visualization of the nematic superconductivity in Cu$_x$Bi$_2$Se$_3$

Cu$_x$Bi$_2$Se$_3$ hosts both topological surface states and bulk superconductivity. It has been identified recently as a topological superconductor (TSC) with an extraordinary nematic, i. e. C2-symmetric, superconducting state and odd-parity pairing. Here, using scanning tunneling microscopy (STM), we directly examine the response of the superconductivity of CuxBi2Se3 to magnetic field. Under out-of-plane fields, we discover elongated magnetic vortices hosting zero-bias conductance peaks consistent with the Majorana bound states expected in a TSC. Under in-plane fields, the average superconducting gap exhibits two-fold symmetry with field orientation; the long C2 symmetry axes are pinned to the dihedral mirror planes under B//=0.5 T but rotate slightly under B//=1.0 T. Moreover, a nodeless Δ4x gap structure is semi-quantitatively determined for the first time. Our data paint a microscopic picture of the nematic superconductivity in CuxBi2Se3 and pose strong constraints on theory.

cond-mat.supr-con↗

arXiv2019

Tumbling to the Top

We propose a new mechanism to generate the couplings of the top quark to a composite Goldstone Higgs, which we dub {\it Global Extended Technicolor} (GETC). Top, techni-fermions and spin-1 mediators arise as bound states of a tumbling chiral gauge theory. We propose a simple model based on a tumbling $SU(4)$ dynamics, which predicts partial compositeness for the top and an $SU(3)$ model with 6 Dirac flavours for the low-energy composite Higgs. Neutron decay bounds require the new dynamics to confine above $10^{6÷7}$ TeV. A simple extension of the basic model allows to generate partial compositeness also for bottom and tau, and a walking dynamics from an intermediate $SU(3)$ theory with 10 flavours (6 light + 4 heavy), whose dynamics can be studied on the Lattice.

hep-ph↗

arXiv2019

Comment on "A critical look at $β$-function singularities at large $N$" by Alanne, Blasi and Dondi

We first briefly review the state-of-the-art of the large $N_f$ gauge-fermion theories and then show that the claim made in the paper by Alanne, Blasi and Dondi that "The singularities in the $β$ function and in the fermion mass anomalous dimension are simultaneously removed providing no hint for a UV fixed point in the large-N limit" is unwarranted. This is so since the author's truncation of the beta function violates the large number of matter fields counting.

hep-ph↗

arXiv2019

Safe Clockwork

In this letter we demonstrate that safe quantum field theories can accommodate the clockwork mechanism upgrading it to a fundamental theory a lá Wilson. Additionally the clockwork mechanism naturally sources Yukawa hierarchies for safe completions of the Standard Model (SM). As proof of concept we investigate a safe Pati-Salam (PS) clockwork structure.

hep-ph↗

arXiv2019

Spontaneous Long-range Vortex-antivortex Pair in the Two-band 2D Superconductor

The relaxation iterative method is used to minimize Ginzburg-Landau model for the two-band superconductor with Josephson-coupling. A stable spontaneous vortex-antivortex pair with long range order has been revealed. Our result appears due to the Josephson-coupling effect, which leads to a linearly-dependence of total free energy on the distance between vortex-antivortex pair, hence accounts for this phenomenon.

cond-mat.supr-con↗

arXiv2019

Safe Trinification

In this work, we provide a UV safe Trinification theory in which the Standard Model is embedded. Using recently developed large number-of-flavor techniques, safety is achieved by adding to the theory gauged vector-like fermions. We find that all gauge, scalar quartic, and Yukawa couplings achieve an interacting ultraviolet fixed point below the Planck scale. We find renormalization group flow solutions matching the Standard Model in the IR, indicating a truly UV completion of the Standard Model. Imposing constraints that realistic Higgs, top, bottom, tau and reasonable neutrino masses are recovered, we find the set of allowed solutions to be quite restrictive. Furthermore, the symmetry breaking scale is predicted to be around 10 TeV, making this model vulnerable to experiment.

hep-ph↗

arXiv2018

Safe Pati-Salam

We provide an asymptotically safe Pati-Salam embedding of the Standard Model. Safety is achieved by adding to the theory gauged vector-like fermions and by employing recently developed large number-of-flavor techniques and results. We show that the gauge, scalar quartic and Yukawa couplings achieve an interacting ultraviolet fixed point below the Planck scale. The minimal model is a relevant example of a Standard Model extension in which unification of all type of couplings occurs because of a dynamical principle, i.e. the presence of an ultraviolet fixed point. This extension differs from the usual Grand Unified Theories scenario in which only gauge couplings unify and become free with the remaining couplings left unsafe. We find renormalization group flow solutions that match the Standard Model couplings values at low energies allowing for realistic safe extensions of the Standard Model.

hep-ph↗

arXiv2018

Is the enhancement of type II radio bursts during CME interactions related to the associated solar energetic particle event?

We investigated 64 pairs of interacting-CME events identified by the simultaneous observations of SOHO and STEREO spacecraft from 2010 January to 2014 August, to examine the relationship between the large SEP events in the energy of 25-60MeV and the properties of the interacting CMEs. We found that during CME interactions the large SEP events in this study were all generated by CMEs with the presence of enhanced type II radio bursts, which also have wider longitudinal distributions comparing to events with the absence of type II radio burst or its enhancement (almost associated with small SEP events). It seems that the signature of type II radio bursts enhancement is a good discriminator between large SEP and small or none SEP event producers during CME interactions. The type II radio burst enhancement is more likely to be generated by CME interactions, with the main CME having larger speed (v), angular width (WD), mass (m) and kinetic energy (E_k), that taking over the preceding CMEs which also have higher v, WD, m and E_k, than those preceding CMEs in CME pairs missing the type II radio bursts or enhancements. Our analysis also revealed that the intensities of associated SEP events correlate negatively with the intersection height of the two CMEs. Most of type-II-enhanced events and SEP events are coincidentally and almost always made by the fast and wide main CMEs that sweeping fully over a relatively slower and narrower preceding CMEs. We suggest that a fast CME with enough energy completely overtaking a relatively narrower preceding CME, especially in low height, can drive more energetic shock signified by the enhanced type II radio bursts. The shock may accelerate ambient particles and lead to large SEP event more easily.

astro-ph.SR↗

arXiv2018

Asymptotic Safety in the Conformal Hidden Sector?

We combine the notion of asymptotic safety (AS) with conformal invariance in a hidden sector beyond the Standard Model. We use the renormalization group (RG) equations as a bridge to connect UV boundary conditions and EW/TeV scale physics and furnish a detailed example in the context of a leptophobic $U(1)'$ model. A broad selection of UV boundary conditions are formulated corresponding to differing AS scenarios, and we find an AS scenario with very strong predictive power, allowing unique determination of most of the parameters in the model. We obtain the interrelationships among the couplings, the transition scale of the fixed point $M_{UV}$ and the generations of quarks coupled to the $Z'$, and especially the correlation between $M_{UV}$ and the top quark Yukawa coupling $Y_t$. Several phenomenological implications of our results are presented for selected $Z'$ masses.

hep-ph↗

arXiv2018

Gauge-Yukawa theories: Beta functions at large $N_f$

We consider the dynamics of gauge-Yukawa theories in the presence of a large number of matter constituents. We first review the current status for the renormalization group equations of gauge-fermion theories featuring also semi-simple groups. In this regime these theories develop an interacting ultraviolet fixed point that for the semi-simple case leads to a rich phase diagram. The latter contains a complete asymptotically safe fixed point repulsive in all couplings. We then add two gauged Weyl fermions belonging to arbitrary representations of the gauge group and a complex, gauged scalar to the original gauge-fermion theory allowing for new Yukawa interactions and quartic scalar self-coupling. Consequently, we determine the leading $1/N_f$ Yukawa and quartic beta functions. Our work elucidates, consolidates and extends results obtained earlier in the literature. We also acquire relevant knowledge about the dynamics of gauge-Yukawa theories beyond perturbation theory. Our findings are applicable to any extension of the standard model featuring a large number of fermions such as asymptotic safety.

hep-ph↗

arXiv2018

Asymptotically Safe Standard Model via Vector-Like Fermions

We construct asymptotically safe extensions of the Standard Model by adding gauged vector-like fermions. Using large number-of-flavour techniques we argue that all gauge couplings, including the hypercharge and, under certain conditions, the Higgs coupling can achieve an interacting ultraviolet fixed point.

hep-ph↗

arXiv2017

Phase structure of complete asymptotically free SU($N_c$) theories with quarks and scalar quarks

We determine the phase diagram of complete asymptotically free SU($N_c$) gauge theories featuring $N_s$ complex scalars and $N_f$ Dirac quarks transforming according to the fundamental representation of the gauge group. The analysis is performed at the maximum known order in perturbation theory. We unveil a very rich dynamics and associated phase structure. Intriguingly we discover that the complete asymptotically free conditions guarantee that the infrared dynamics displays long distance conformality, and in a regime when perturbation theory is applicable. We conclude our analysis by determining the quantum corrected potential of the theory and summarising the possible patterns of radiative symmetry breaking. These theories are of potential phenomenological interest as either elementary or composite ultraviolet finite extensions of the Standard Model.

hep-ph↗

arXiv2016

Conformal Complex Scalar Singlet Extensions of the Standard Model: Symmetry Breaking Patterns and Phenomenology

We consider a conformal complex singlet extension of the Standard Model with a Higgs portal interaction. Two different scenarios depending on whether the global U(1) symmetry is broken or not have been studied. In the unbroken phase, the decay of the complex singlet is protected by the global U(1) symmetry which leads to an ideal cold dark matter candidate. In the broken phase, we are able to provide a second Higgs at $554\,\rm{GeV}$. In addition, gauging the global U(1) symmetry, we can construct an asymptotically safe U(1)' leptophobic model. We combine the notion of asymptotic safety with conformal symmetry and use the renormalization group equations as a bridge to connect UV boundary conditions and Electroweak/ TeV scale physics. We also provide a detailed example to show that these boundary conditions will lead to phenomenological signatures such as diboson excesses which could be tested at the LHC.

hep-ph↗

arXiv2016

Detection prospects for conformally constrained vector-portal dark matter

We work with a UV conformal U(1)' extension of the Standard Model, motivated by the hierarchy problem and recent collider anomalies. This model admits fermionic vector portal WIMP dark matter charged under the U(1)' gauge group. The asymptotically safe boundary conditions can be used to fix the coupling parameters, which allows the observed thermal relic abundance to constrain the mass of the dark matter particle. This highly restricts the parameter space, allowing strong predictions to be made. The parameter space of several UV conformal U(1)' scenarios will be explored, and both bounds and possible signals from direct and indirect detection observation methods will be discussed.

hep-ph↗

arXiv2016

Conformal Complex Singlet Extension of the Standard Model: Scenario for Dark Matter and a Second Higgs Boson

We consider a conformal complex singlet extension of the Standard Model with a Higgs portal interaction. The global $U(1)$ symmetry of the complex singlet can be either broken or unbroken and we study each scenario. In the unbroken case, the global $U(1)$ symmetry protects the complex singlet from decaying, leading to an ideal cold dark matter candidate with approximately 100 GeV mass along with a significant proportion of thermal relic dark matter abundance. In the broken case, we have developed a renormalization-scale optimization technique to significantly narrow the parameter space and in some situations, provide unique predictions for all the model's couplings and masses. We have found there exists a second Higgs boson with a mass of approximately $550\,\rm{GeV}$ that mixes with the known $125\,\rm{GeV}$ Higgs with a large mixing angle $\sinθ\approx 0.47$ consistent with current experimental limits. The imaginary part of the complex singlet in the broken case could provide axion dark matter for a wide range of models. Upon including interactions of the complex scalar with an additional vector-like fermion, we explore the possibility of a diphoton excess in both the unbroken and the broken cases. In the unbroken case, the model can provide a natural explanation for diphoton excess if extra terms are introduced providing extra contributions to the singlet mass. In the broken case, we find a set of coupling solutions that yield a second Higgs boson of mass $720\,\rm{GeV}$ and an $830\,\rm{GeV}$ extra vector-like fermion $F$, which is able to address the $750\,\rm{GeV}$ LHC diphoton excess. We also provide criteria to determine the symmetry breaking pattern in both the Higgs and hidden sectors.

hep-ph↗