Usually a warrant follows the investigation when a DA feels enough evidence is collected to get a conviction (to avoid double jeopardy) and is the official way of doing it. In some countries provision is made for an occasion on which somebody may catch another in the process of committing a crime; commonly called "citizen's arrest", the law normally states that a person, whether uniformed officer or member of the public, can place another person under arrest if they have reasonable suspicion that the other has been/is in commission of a crime.
Yes, of course. An arrest warrant is a command from a judge to arrest a person. Usually a police officer has no choice and must arrest.
No.
No, a police officer cannot issue a warrant for your arrest only a judge or court magistrate can do that.
It does not seem reasonable or possible.
A police officer must have probable cause in order to arrest someone. They can arrest a person if they see a crime taking place or if an arrest warrant has been issued.
no
Without a warrant you must find reasonable grounds to arrest someone, whereas with a warrant your reason to arrest the suspect already exists. Without a warrant a Police Officer can arrest anyone without permission of a Magistrate as long as they follow the correct procedures so their arrest is lawful, which is unlike an arrest with a warrant where you must be granted the warrant to be able to arrest that person. Without a warrant, a Police Officer can mess the arrest up and make it an unlawful arrest but with a warrant it is very unlikely that they make it an unlawful arrest.
Probable cause or warrant
A person is "under arrest" when a police officer charges them with a crime and chooses to take them to the police station to be processed for it. For example, if someone commits a crime, they are technically under arrest when a police officer witnesses the crime or has a warrant for the arrest and tells the criminal "You are under arrest." Typical procedure after this is to put handcuffs on the criminal and read them their Miranda rights (you have the right to remain silent etc). Handcuffs alone do not mean arrest, but i'm pretty sure its illegal for a police officer to handcuff someone without grounds to arrest them. As a side note, the person doing the arrest does not have to be a sworn in police officer. In Citizen's arrest cases, anyone with arresting powers like a bounty hunter can also place someone under arrest.
An arrest refers to the lawful deprivation of the freedom of an individual by a peace officer. A police officer may arrest a person if he reasonably believes a crime has been committed without a warrant.
A "stop and frisk search," where police search you for their protection or incidental to an arrest; or when contraband is in plain view of the officer.
If there is a warrant out for you and the police know where you are, they can arrest you.