Here's your look at five stories we're following today:

1. New defense secretary: President Barack Obama is expected to nominate Ashton Carter, a physicist with years of experience at the Pentagon (and 1972 graduate of Abington High School), as the next secretary of defense.

2. Manayunk disappearance: The search for Shane Montgomery, who disappeared after leaving a bar in Manayunk last week, continues. A vigil outside the student union is planned for this evening at the West Chester University student's college.

3. GSK layoffs: GlaxoSmithKline executives are expected to address U.S. workers today to detail how the company will implement $1.57 billion in cost cuts, a process that may include layoffs in the Philadelphia area.

4. City Hall tree returns: The official lighting ceremony for City Hall's Christmas tree -- absent from the courtyard during the past two years due to Dilworth Park construction -- takes place this evening.

5. Trial in hoops star's death: The murder trial for Maria Garcia-Pellon, accused of fatally stabbing her husband, former University of Pennsylvania basketball star Matthew White, continues today. Her attorney is arguing that the woman's mental illness was behind the slaying.