arXiv subjects

Cao H. Nam

Publications and source records attributed to Cao H. Nam.

36 records · Page 2Linked to original sources

arXiv2022

Holographic model with power-law Maxwell field for color superconductivity

Studying the color superconductivity (CSC) phase is essential to understand the physics in the core of the neutron stars which is the only known context where the CSC phase might appear due to the gravitational force squeezing the matter to a sufficiently high density. We propose a simple holographic dual description of the CSC phase transition in the realistic Yang-Mills theory with the power-law Maxwell field. We find the CSC phase transition with the large color number in the deconfinement phase, which is not found in the case of the usual Maxwell field, if the power parameter characterizing for the power-law Maxwell field is sufficiently lower than one but above $1/2$ and the chemical potential is above a critical value. However, the power parameter is not arbitrary below one because when this parameter is sufficiently far away from one it leads to the occurrence of the CSC state in the confinement phase which is not compatible with a nonzero vacuum expectation value of the color nonsinglet operator.

hep-th↗

arXiv2022

Implications of quantum gravity for dark matter in the brane-world scenario

Based on the swampland program establishing the constraints that an effective field theory must satisfy in order to come from quantum gravity, we point to that if this program is true the brane-world scenario with the branon dark matter (DM) would be ruled out without needing the experimental observations. In other words, the constraints of quantum gravity imply that the branons must be absorbed by the Kaluza-Klein (KK) gauge bosons which are the off-diagonal components of the bulk metric to become their longitudinal modes. Interestingly, the KK gauge bosons behave as the DM and hence it leads to a geometric unification of gravity and the DM, as a natural feature of the brane-world scenario completed into quantum gravity in the ultraviolet. In addition, the KK gauge boson DM would open a particularly promising observation window to search for the DM coupling very weakly to the SM in the cosmic microwave background and the spectrum of the primordial gravitational waves.

hep-ph↗

arXiv2022

Entanglement entropy and Page curve of black holes with island in massive gravity

By applying the island rule proposed recently, we compute the entanglement entropy of Hawking radiation and study the Page curve for the eternal black holes in massive gravity. We investigate for both the neutral and charged black holes which the corresponding results of Schwarzschild and Reissner-Nordström black holes are restored in the limit of massless graviton. We show for the neutral and non-extremal charged black holes that the island is not formed at the early times of the evaporation and hence the entanglement entropy increases linearly in time. However, for the extremal charged black hole, the calculation of the entanglement entropy at the early times without the island is ill-defined because the metric is divergent at the curvature singularity. This implies that new physics in the UV region must be taken into account to make the metric behaving smoothly at the very short distances. At the late times, with the emergence of one island near the event horizon, the entanglement entropy is saturated by the Bekenstein-Hawking entropy of black holes. In addition, we analyze the impact of massive gravity parameters on the size of island, the entanglement entropy, the Page time, and the scrambling time in detail.

hep-th↗

arXiv2022

Dark charge versus electric charge

We revisit a theory that proposes a dark charge, $D$, as a dequantization of the electric charge, $Q$. We find that the general arguments of anomaly cancelation and fermion mass generation yield both $D$ and $Q$, nontrivially unified with the weak isospin $T_i$ $(i={1,2,3})$ in a novel gauge symmetry, $SU(3)_C\otimes SU(2)_L\otimes U(1)_Y\otimes U(1)_N$, where $Y$ and $N$ determine $Q$ and $D$ through the $T_3$ operator, i.e. $Q=T_3+Y$ and $D=T_3+N$, respectively. A new observation is that fundamental particles possess a dynamical dark charge which governs both neutrino mass and dark matter, where the neutrino mass is determined via a canonical seesaw, while the dark matter stability is ensured by electric and color charge conservations. We examine the mass spectra of fermions, scalars, and gauge bosons, as well as their interactions, taking into account the kinetic mixing effect of $U(1)_{Y,N}$ gauge fields. The new physics phenomena at colliders are examined. The dark matter relic density and detection are discussed.

hep-ph↗

arXiv2022

Probing dark gauge boson via Einstein-Cartan portal

Einstein-Cartan gravity which is an alternative formulation of general relativity introduces new degrees of freedom contained in the torsion field which encodes the torsion feature of spacetime. Interestingly, the torsion field couples to all fermions through its axial-vector mode with a universal coupling $η=1/8$ which is possible to change under the quantum effects. We argue that Einstein-Cartan gravity provides a significant portal to probe $A'$ dark gauge boson which resides in dark sector existing as an invisible world parallel to our own and couples to the standard model (SM) particles through only the kinetic mixing. For the (very) small kinetic mixing, searches for the $A'$ from Drell-Yan processes are insensitive due to the suppressed production cross-section and the considerable SM backgrounds. However, through the mediation of torsion field the $pp$ collisions produce dark-sector fermions which would significantly produce the $A'$ due to unsuppressed dark gauge coupling. We explore the potential production modes of the $A'$ through bremsstrahlung off dark-sector fermion and the cascade decays. Einstein-Cartan gravity suggests the torsion mass $\gtrsim\mathcal{O}(4)$ TeV for $η$ varying around the classical value since the present scenarios would tend to produce the $A'$ with the high boost and large missing transverse momentum from dark-sector fermions where the SM backgrounds are low. On the other hand, the $A'$ search via Einstein-Cartan portal can reach even for the signal events to be not large and is also sensitive to the (very) small kinetic mixing as long as the decay channels of the $A'$ to dark-sector particles are inaccessible.

hep-ph↗

arXiv2021

Dark matter in the fully flipped 3-3-1-1 model

We present the features of the fully flipped 3-3-1-1 model and show that this model leads to dark matter candidates naturally. We study two dark matter scenarios corresponding to the triplet fermion and singlet scalar candidates, and we determine the viable parameter regimes constrained from the observed relic density and direct detection experiments.

hep-ph↗

arXiv2021

A more realistic holographic model of color superconductivity with the higher derivative corrections

In this paper, we have constructed a bottom-up holographic model for the color superconductivity (CSC) of the Yang-Mills theory with including the higher derivative corrections which allow to study the CSC phase with the color number $N_c\geq2$. First, we consider the CSC phase transition in the context of Einstein-Gauss-Bonnet (EGB) gravity. We analyze the Cooper pair condensate in the deconfinement and confinement phases which are dual to the planar GB-RN-AdS black hole and GB-AdS soliton, respectively, where the backreaction of the matter part is taken into account. By examining the breakdown of the Breitenlohner-Freedman bound in the background of the planar GB-RN-AdS black hole, we find that the positive GB coupling parameter $α>0$ leads to a lower upper bound of the color number in comparison to Einstein gravity where the CSC phase for $N_c\geq2$ is not realized. But, with the $α<0$ case it is possible to observe the Cooper pair condensate for $N_c\geq2$ with the reasonable magnitude of $α$. This is confirmed and the corresponding phase diagram is found by solving numerically the equations of motion for the gravitational system. In addition, we show that the CSC phase disappears in the confinement phase for the magnitude of $α$ below a certain value which means that beyond that value it might lead to the breakdown region of the EGB gravity in investigating the CSC phase. However, the CSC phase transition occurring with $N_c\geq2$ requires the magnitude of the GB coupling parameter to be rather large. As a result, the GB term would no longer be considered as the correction and it also violates the boundary causality bound. We resolve this problem by including additionally the higher derivative correction for the Maxwell electrodynamics and the non-minimal coupled Maxwell field.

hep-th↗

arXiv2021

Canonical seesaw implication for two-component dark matter

We show that the canonical seesaw mechanism implemented by the $U(1)_{B-L}$ gauge symmetry provides two-component dark matter naturally. The seesaw scale that breaks $B-L$ defines a residual gauge symmetry to be $Z_6=Z_2\otimes Z_3$, where $Z_2$ leads to the usual matter parity, while $Z_3$ is newly recognized, transforming quark fields nontrivially. The dark matter components -- that transform nontrivially under the matter parity and $Z_3$, respectively -- can gain arbitrary masses, despite the fact that the $Z_3$ dark matter may be heavier than the light quarks $u,d$. This dark matter setup can address the XENON1T anomaly recently observed and other observables, given that the dark matter masses are nearly degenerate, heavier than the electron and the $B-L$ gauge boson $Z'$, as well as the fast-moving $Z_3$ dark matter has a large $B-L$ charge, while the $Z'$ is viably below the beam dump experiment sensitive regime.

hep-ph↗

arXiv2020

Multicomponent dark matter in noncommutative $B-L$ gauge theory

It is shown that for a higher weak isospin symmetry, $SU(P)_L$ with $P\geq 3$, the baryon minus lepton charge $B-L$ neither commutes nor closes algebraically with $SU(P)_L$ similar to the electric charge $Q$, which all lead to a $SU(3)_C\otimes SU(P)_L\otimes U(1)_X\otimes U(1)_N$ gauge completion, where $X$ and $N$ determine $Q$ and $B-L$, respectively. As a direct result, the neutrinos obtain appropriate masses via a canonical seesaw. While the version with $P=3$ supplies the schemes of single-component dark matter well established in the literature, we prove in this work that the models with $P\geq 4$ provide the novel scenarios of multicomponent dark matter, which contain simultaneously at least $P-2$ stable candidates, respectively. In this setup, the multicomponet dark matter is nontrivially unified with normal matter by gauge multiplets, and their stability is ensured by a residual gauge symmetry which is a remnant of the gauge symmetry after spontaneous symmetry breaking. The three versions with $P=4$ according to the new lepton electric charges are detailedly investigated. The mass spectrum of the scalar sector is diagonalized when the scale of the $U(1)_N$ breaking is much higher than that of the usual 3-4-1 symmetry breaking. All the interactions of gauge bosons with fermions and scalars are obtained. We figure out viable parameter regimes given that the multicomponent dark matter satisfies the Planck and (in)direct detection experiments.

hep-ph↗

arXiv2020

Flipped $U(1)$ extended Standard Model and Majorana dark matter

We propose a general flavor-independent extension of the Standard Model (SM) with the minimal particle content, based on the symmetry $SU(3)_C\times SU(2)_L\times U(1)_{Y'}\times U(1)_X\times Z_2$. In this scenario, the charge operator is identified in terms of the charges of two $U(1)$ gauge symmetries. The light neutrino masses are generated via Type-I seesaw mechanism only with two heavy right-handed neutrinos acquiring their Majorana masses through the $U(1)_{Y'}\times U(1)_X$ symmetry breaking. We study various experimental constraints on the parameters of the model and investigate the phenomenology of the right-handed neutrino dark matter (DM) candidate assigned a $Z_2$-odd parity. We find that the most important constraints are the observed DM relic abundance, the current LHC limits, and the ambiguity of the SM neutral gauge boson mass.

hep-ph↗

arXiv2020

Effects of massive gravity on $p$-wave holographic superconductor

In this paper, we have analytically investigated $p$-wave holographic superconductor in the framework of massive gravity in the probe limit. We obtained the analytical expressions for the critical temperature, the value of the condensate operator, and the difference of the free energy between the superconductor and normal phases. We studied the behavior of these quantities in the presence of the mass of graviton, which is found to be dependent almost on the sign of the massive gravity couplings. The critical temperature becomes (lower)higher and the condensate value gets (larger)smaller with (decreasing)increasing the massive gravity couplings or increasing the mass of graviton with the sufficiently (negative)positive massive gravity couplings. This fact corresponds to that the superconductor phase is (more)less thermodynamically favored.

hep-th↗

arXiv2020

17 MeV Atomki anomaly from short-distance structure of spacetime

An anomaly observed recently in the $^8$Be nuclear transition by the Atomki collaboration hints at a weakly-coupled, light new gauge boson with a mass of about $17$ MeV. In this paper, we propose that this new gauge boson comes from a short-distance structure of the spacetime, rather than from an extension of the Standard Model through adding an extra $\mathrm{U}(1)$ gauge symmetry. The dominant contribution to the relevant matrix element of the $^8$Be nuclear transition is given by the axial couplings. In order to account for the $^8$Be anomaly and satisfy the current experimental constraints, the coupling constant of the new gauge boson should be about $\mathcal{O}(10^{-4}-10^{-5})$. Our theoretical model allows understanding the origin of the smallness of the coupling constant, which is still missing or being incompletely understood in the models at which the new gauge boson has the axial couplings.

hep-ph↗

arXiv2019

A flipped $U(1)_R$ extension of the Standard Model

In this work, we study an extension of the Standard Model (SM) based on the gauge symmetry $SU(3)_C\times SU(2)_L\times U(1)_{Y'}\times U(1)_R$ where only the right-handed fermions have nonzero $U(1)_R$ charge and the $U(1)_Y$ weak hypercharge of the SM is identified as a combination of the $U(1)_{Y'}$ and $U(1)_R$ charges. The gauge charge assignment of the fields is constrained by the conditions of the anomaly cancellation and the gauge invariance of the Yukawa couplings. The light neutrino masses are generated via the type-I seesaw mechanism where the Majorana masses of the right-handed neutrinos are related to the $U(1)_{Y'}\times U(1)_R$ symmetry breaking scale. Then, we discuss the constraints on the free parameters of the model from the various current experiments, such as precision measurement of the total $Z$ width, $ρ$ parameter, atomic parity violation of Cesium, LEP and LHC bounds. In addition, we investigate the potential of probing for the signal of the new neutral gauge boson based on the forward-backward asymmetry for the process $e^+e^-\rightarrowμ^+μ^-$ which is the most sensitive mode at ILC.

hep-ph↗

arXiv2019

Gauss-Bonnet holographic superconductors in exponential nonlinear electrodynamics

The low-energy limits of the string theory lead to the higher-order curvature corrections for Einstein gravity. Also, they give the higher-order derivative corrections for the Maxwell or linear electrodynamics, which suggests the nonlinear electrodynamics. Inspired by this, in this paper we investigate $d$-dimensional holographic superconductors in the probe limit in the framework of Einstein-Gauss-Bonnet gravity and exponential nonlinear electrodynamics. Based on the Sturm-Liouville eigenvalue method, we compute the critical temperature, the condensation value, and the critical exponent. It is observed that the critical temperature decreases when the Gauss-Bonnet (GB) parameter or the nonlinear parameter increases, but it increases with the higher dimension of the spacetime at the efficiently low charge density. In addition, we found that the condensation value becomes larger as increasing the GB parameter, the nonlinear parameter as well as the spacetime dimension. Finally, we calculate the optical conductivity and study the effects of the GB term and exponential nonlinear electrodynamics on superconducting energy gap.

hep-th↗

arXiv2019

Charged AdS black holes in Gauss-Bonnet gravity and nonlinear electrodynamics

New five-dimensional charged AdS black hole solutions are found in Einstein-Gauss-Bonnet gravity and the nonlinear electrodynamics. These solutions include regular black holes as well as extremal black holes. The first law of the black hole thermodynamics is confirmed in the extended phase space where the cosmological constant is treated as the pressure. The first and second order phase transitions are investigated by observing the behavior of the heat capacity at constant pressure and the Gibbs free energy. In addition, the equation of state for the black holes and their $P-V$ criticality are studied. Finally, the critical exponents are found to be the same as those of the Van der Waals fluid.

gr-qc↗

arXiv2019

Effects of string cloud on Gauss-Bonnet holographic superconductors

The effects of the string cloud on higher-dimensional holographic superconductors in Einstein-Gauss-Bonnet gravity are investigated in the probe limit. The critical temperature is analytically obtained using Sturm-Liouville eigenvalue method. It is observed that the critical temperature only exists in an allowed region of the parameter space. Also, the presence of the string cloud with the sufficiently large density should prevent the the existence of the critical temperature. As increasing the string cloud density parameter, the critical temperature decreases in the region of the sufficiently low charge density but increases in the region of the sufficiently high charge density. Whereas, the presence of Gauss-Bonnet terms always makes the critical temperature decreasing. In addition, the expression of the condensation operator and the critical exponent are computed analytically.

hep-th↗

arXiv2014

A covariantly foliated higher dimensional space-time: Implications for short distance gravity and BSM physics

We consider the space-time at short distances in which it is described by a $D$-dimensional manifold (bulk) carrying out the principal bundle structure. As a result, this space-time manifold is foliated in the covariant way by the $(D-4)$-dimensional submanifolds, realized as the space-like internal spaces, that are smooth copies of the Lie group $G$ considered in this paper as the special unitary group. The submanifolds being transversal to the internal spaces are realized as the external spaces and in fact identified as the usual $4$-dimensional world. The fundamental degrees of freedom determining the geometrical dynamics of the bulk corresponding with short distance gravity are given by the gauge fields, the external metric field and the modulus fields setting dynamically the volume of the internal spaces. These gauge fields laying the bulk is to point precisely out the local directions of the external spaces which depend on the topological non-triviality of the space-time principal bundle. The physical size of the internal spaces is fixed dynamically by the moduli stabilization potential which completely arise from the intrinsic geometry of the bulk. A detail description of the low energy bulk gravity in the weak field limit is given around the classical ground state of the bulk. Additionally, we investigate the dynamics of the fundamentally $4$-dimensional Weyl spinor fields and the fields of carrying out the non-trivial representations of the Lie group $G$ propagating in the bulk in a detail study. These results suggest naturally the possible solutions to some the experimental problems of Standard Model, the smallness of the observed neutrino masses and a dark matter candidate.

hep-th↗

arXiv2014

Gauge theory of quantum gravity

The gravity is classically formulated as the geometric curvature of the space-time in general relativity which is completely different from the other well-known physical forces. Since seeking a quantum framework for the gravity is a great challenge in physics. Here we present an alternative construction of quantum gravity in which the quantum gravitational degrees of freedom are described by the non-Abelian gauge fields characterizing topological non-triviality of the space-time. The quantum dynamics of the space-time thus corresponds to the superposition of the distinct topological states. Its unitary time evolution is described by the path integral approach. This result will also be suggested to solve some major problems in physics of the black holes.

hep-th↗