The CP-restoring phase transition at theta = pi and high temperature is investigated using two related models that aim to describe the low-energy phenomenology of QCD, the NJL model and the linear sigma model coupled to quarks. Despite many similarities between the models, different predictions for the order of the phase transition result. Using the Landau-Ginzburg formalism, the origin of this difference is traced back to a non-analytic vacuum term at zero temperature that is present in the NJL model, but usually not included in the linear sigma model. Due to the absence of explicit CP violation, this term always alters the qualitative aspects of the high temperature phase transition at theta = pi, just as for theta = 0 in the chiral limit.
Recently, it has been conjectured that deconfining phase transition in SU(N_c) pure Yang-Mills theories is continuously connected to a quantum phase transition in softly broken N=1 super Yang-Mills on R^{1,2}*S^1. We exploit this conjecture to study the strength of the transition and deconfining temperature as a function of the vacuum angle theta in pure Yang-Mills. We find that the transition temperature is a decreasing function of theta in [0, π), in an excellent agreement with recent lattice simulations. We also predict that the transition becomes stronger for the same range of theta, and c…
We present recent investigations on the vector and axial-vector transitions of the baryon antidecuplet within the framework of the self-consistent SU(3) chiral quark-soliton model, taking into account the 1/N_c rotational and linear m_s corrections. The main contribution to the electric-like transition form factor comes from the wave-function corrections. This is a consequence of the generalized Ademollo-Gatto theorem. It is also found that in general the leading-order contributions are almost canceled by the rotational 1/N_c corrections. The results are summarized as follows: the vector and t…
We investigate the dependence of four-dimensional SU(N) gauge theories on the topological theta term at finite temperature and, in particular, across the deconfinement transition. For this purpose, we exploit the lattice formulation of the theory and present numerical results for the expansion of the free energy up to O(theta^6), for N=3 and N=6. Our numerical analysis shows that the theta dependence of 4D SU(N) gauge theory experiences a drastic change across the deconfinement transition: the low-temperature phase is characterized by a large-N scaling with theta/N as relevant variable, while …
Using the twisted partition function on R^3 x S^1, we argue that the deconfinement phase transition in pure Yang-Mills theory for all simple gauge groups is continuously connected to a quantum phase transition that can be studied in a controlled way. We explicitly consider two classes of theories, gauge theories with a center symmetry, such as SU(N_c) gauge theory for arbitrary N_c, and theories without a center symmetry, such as G_2 gauge theory. The mechanism governing the phase transition is universal and valid for all simple groups. The perturbative one-loop potential as well as monopole-i…
Theta vacuum effects on the QCD phase structure in the μ-T plane are studied by using the Polyakov-loop extended Nambu-Jona-Lasinio model and its extension, where μis the quark chemical potential and T is temperature, respectively. As the parameter θof the theta vacuum increases, the chiral transition becomes stronger. For large θ, it eventually becomes first order even at zero μ.
We consider corrections to the unification of down-quark and charged-lepton Yukawa couplings in supersymmetric GUTs, which links the large nu_tau-nu_mu mixing angle to b -> s transitions. These corrections generically occur in simple grand-unified models with small Higgs representations and affect s -> d and b -> d transitions via the mixing of the corresponding right-handed superpartners. On the basis of a specific SUSY-SO(10) model, we analyze the constraints from K-Kbar and B-Bbar mixing on the additional \tilde{d}_R-\tilde{s}_R rotation angle theta. We find that epsilon_K already sets a st…
When the neutrino density is very high, as in core-collapse supernovae, neutrino-neutrino interactions are not negligible and can appreciably affect the evolution of flavour. The physics of these phenomena is briefly highlighted, and their effects are shown on observable energy spectra from a future galactic supernova within two-neutrino and three-neutrino frameworks. Detection of such effects could provide a handle on two unknowns: the neutrino mass hierarchy, and the mixing angle theta(13).
In this work, extending a previous study at zero temperature ($T=0$), we perform a systematic study of the modifications to the QCD vacuum energy density $ε_{vac}$ in the finite-temperature case, above the chiral transition at $T_c$, caused by a nonzero value of the parameter $θ$, using two different effective Lagrangian models which implement the $U(1)$ axial anomaly of the fundamental theory and which are both well defined also above $T_c$. In particular, we derive (and critically compare) the expressions for the topological susceptibility $χ$ and for the second cumulant $c_4$ starting from …
We consider QED on a two-dimensional Euclidean torus with $f$ flavors of massless fermions and flavor-dependent chemical potentials. The dependence of the partition function on the chemical potentials is reduced to a $(2f-2)$-dimensional theta function. At zero temperature, the system can exist in an infinite number of phases characterized by certain values of traceless number densities and separated by first-order phase transitions. Furthermore, there exist many points in the $(f-1)$-dimensional space of traceless chemical potentials where two or three phases can coexist for $f=3$ and two, th…
When inverse seesaw meets inverse electroweak phase transition: a novel path to leptogenesis
Tsung-Dao Lee Institute and School of Physics and Astronomy, Shanghai Jiao Tong University（上海交通大学物理与天文学院）；Marietta Blau Institute for Particle Physics, Austrian Academy of Sciences（奥地利科学院马里埃塔·布劳粒子物理研究所）；Department of Physics and Astronomy, University of Nebraska（内布拉斯加大学物理与天文系）；School of Physics, Beihang University（北京航空航天大学物理学院）
We investigate the properties of the deconfining/chiral restoring transition for two flavor QCD in presence of a uniform background magnetic field. We adopt a standard staggered discretization of the fermion action and a lattice spacing of the order of 0.3 fm. We explore different values of the bare quark mass, corresponding to pion masses in the range 200 - 480 MeV, and magnetic fields up to |e|B ~ 0.75 GeV^2. The deconfinement and chiral symmetry restoration temperatures remain compatible with each other and rise very slightly (< 2 % for our largest magnetic field) as a function of the magne…
We investigate chiral symmetry breaking and strong CP violation effects in the phase diagram of strongly interacting matter. We demonstrate the effect of strong CP violating terms on the phase structure at finite temperature and densities in a 3-flavor Nambu-Jona-Lasinio (NJL) model including the Kobayashi-Maskawa-t'Hooft (KMT) determinant term. This is investigated using an explicit structure for the ground state in terms of quark-antiquark condensates for both in the scalar and the pseudoscalar channels. CP restoring transition with temperature at zero baryon density is found to be a second …
